Microbes and Microbial Products as Herbicides - ACS Publications

Chapter 1

Microbes and Microbial Products as Herbicides A n Overview Robert E. Hoagland

Downloaded by 92.63.110.177 on January 26, 2017 | http://pubs.acs.org Publication Date: September 25, 1990 | doi: 10.1021/bk-1990-0439.ch001

Southern Weed Science Laboratory, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 350, Stoneville, MS 38776

Microbes (plant pathogens) and microbial products (phytotoxins) have been shown to have potential as weed control agents. Growth in the interest in these alternative weed control methods has been brought about by a need for less persistent, more selective, and more environmentally safe herbicides. Broad-spectrum and selective activity are concepts important to the development of a weed control agent. Generally, pathogens are host-specific while phytotoxins have a wider range of activity. Over the past several years, new pathogens and microbial phytotoxins from pathogens and other microorganisms have been discovered which can be added to the arsenal of biological weed control weapons. Pathogens, and in some cases phytotoxins, may be used directly on the target species; alternatively, phytotoxins or compounds from non-pathogenic organisms may provide template chemistries for new synthetic herbicide designs. Pathogens also have potential for use in integrated approaches to weed management programs, where the organisms can tolerate the presence of other agricultural chemicals and where they may interact synergistically with herbicides. Genetic engineering and microbial strain selection to increase pathogen virulence, alter host range, and enhance interactions with other chemical regulators or synergists may promote infectivity and weed control efficacy. This chapter reviews some recent advances in the area of isolation and identification of novel microbial chemistries with phytotoxic properties and presents perspectives on other aspects of the use of microbes and natrually occuring microbial compounds for weed control. The d e v e l o p e d n a t i o n s o f t h e w o r l d a r e g e n e r a l l y a b l e t o produce more f o o d t h a n i s n e c e s s a r y t o f e e d t h e i r p o p u l a c e . T h i s h i g h

This chapter not subject to U.S. copyright Published 1990 American Chemical Society

Hoagland; Microbes and Microbial Products as Herbicides ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

1.

HOAGLAND

3

An Overview


p r o d u c t i v i t y and t h e s e s u r p l u s e s are l a r g e l y t h e r e s u l t o f t h e use o f f e r t i l i z e r s and o t h e r a g r o c h e m i c a l s t o c o n t r o l weeds, i n s e c t s , and d i s e a s e s i n c r o p s . A l t h o u g h many o f t h e w o r l d ' s n a t i o n s produce more f o o d s t u f f s than are n e c e s s a r y t o f e e d t h e i r own p e o p l e , g l o b a l f o o d p r o d u c t i o n l i e s i n p r e c a r i o u s b a l a n c e . The d i f f e r e n c e between a g r i c u l t u r a l s u r p l u s and s h o r t a g e depends on o n l y a 5% change i n w o r l d w i d e a g r i c u l t u r a l acreage (1). Estimates are t h a t a g r i c u l t u r a l o u t p u t w i l l need t o i n c r e a s e 30% by t h e y e a r 2000 t o s u p p o r t t h e p r o j e c t e d w o r l d p o p u l a t i o n o f 6.6 b i l l i o n (2). Modern a g r i c u l t u r a l p r a c t i c e s r e l y h e a v i l y on c h e m i c a l methods o f p e s t c o n t r o l , a l t h o u g h a few b i o l o g i c a l c o n t r o l endeavors have a l s o been s u c c e s s f u l . Economics o f Weed Problems. Of t h e n e a r l y 300,000 s p e c i e s o f h i g h e r p l a n t s i n t h e w o r l d , o n l y about 10% a r e weeds; about 1,800 weeds are r e s p o n s i b l e f o r economic l o s s e s i n a g r i c u l t u r a l p r o d u c t i o n (2). About 300 weed s p e c i e s cause s e r i o u s economic l o s s e s i n c u l t i v a t e d w o r l d c r o p s . However, o n l y about 200 weed s p e c i e s a r e r e s p o n s i b l e f o r 95% o f t h e weed problems f a c e d by t h o s e i n v o l v e d i n t h e p r o d u c t i o n o f f o o d and f i b e r (1). Weeds a r e c o s t l y . Weeds accounted f o r n e a r l y 42% o f t h e l o s s e s o f c r o p s t o p e s t s i n t h e U.S. i n 1971 ( T a b l e I ) . In t h e U.S. a l o n e , weeds were e s t i m a t e d t o cause Table I.

Annual C o s t s o f P l a n t P e s t s o f Crops

Pest

Losses (x 1,000)

Diseases Insects Nematodes Weeds Total

$3,152,815 2,965,344 372,335 2,459,630 8,950,124

$

Control (x 1,000)

Total (x 1,000)

115,000 425,000 16,000 2,551,050 3,107,050

$ 3,267,815 3,390,344 388,335 5,010,680 12,057,174

Reproduced w i t h p e r m i s s i o n from Ref. and S o n s .

(5).

Total (%) 27.1 28.1 3.2 41.6 100.0

C o p y r i g h t 1982 John W i l e y

r e d u c t i o n s i n p r o d u c t i v i t y r e s u l t i n g i n monetary l o s s e s f o r f i e l d c r o p s and v e g e t a b l e s o f o v e r $7 b i l l i o n p e r y e a r i n 1975-79 ( T a b l e II). Beyond t h e l o s s e s i n p r o d u c t i v i t y a r e a c t u a l c o s t s o f p e s t i c i d e s and t h e i r a p p l i c a t i o n . From t h e l a t e I 9 6 0 ' s through 1987, t h e use o f h e r b i c i d e s i n the U.S. exceeded t h e use o f i n s e c t i c i d e s and f u n g i c i d e s combined ( F i g u r e 1 ) . On a g l o b a l s c a l e , o t h e r d a t a shows t h a t h e r b i c i d e s accounted f o r 44% o f t o t a l p e s t i c i d e s a l e s i n 1985 ( F i g u r e 2 ) . Combined g l o b a l p e s t i c i d e s a l e s i n 1985 were e q u i v a l e n t t o about $16 b i l l i o n U.S. A l t h o u g h advances i n weed c o n t r o l have been a c h i e v e d , weeds c o n t i n u e t o cause a g r i c u l t u r a l l o s s e s . Thus, new weed c o n t r o l s t r a t e g i e s a r e needed t o augment and/or r e p l a c e l e s s - t h a n - s u c c e s s f u l s t r a t e g i e s . P e s t i c i d e s a r e c r u c i a l f o r maintanence o f our modern f o o d p r o d u c t i o n . However, c u r r e n t p a t t e r n s o f use and misuse o f c h e m i c a l p e s t i c i d e s have r e s u l t e d i n some e n v i r o n m e n t a l p r o b l e m s . Ground w a t e r c o n t a m i n a t i o n by h e r b i c i d e s and o t h e r p e s t i c i d e s may t h r e a t e n


4

MICROBES AND MICROBIAL PRODUCTS AS HERBICIDES

T a b l e I I . E s t i m a t e d Average Annual Losses Due t o Weeds i n S e v e r a l Commodity Groups 1n t h e U n i t e d S t a t e s , 1975-1979 Average annual monetary l o s s e s

Commodity group

($ x 1,000)


F i e l d crops Vegetables F r u i t s and n u t s Forage seed c r o p s Reproduced w i t h p e r m i s s i o n from R e f . Science Society of America.

6,408,183 619,072 441,449 37,400 (£).

C o p y r i g h t 1984 Weed

p u b l i c h e a l t h . G e n e r a l l y , t h e r e has been i n c r e a s e d p u b l i c c o n c e r n about t h e s a f e t y o f a g r i c u l t u r a l c h e m i c a l s , i n c l u d i n g h e r b i c i d e s (£)» i n some c a s e s r e s u l t i n g i n p u b l i c r e f e r e n d a t o reduce t h e use o f t h e s e compounds. I f t h i s t r e n d c o n t i n u e s , t o t a l mechanical a n d / o r b i o l o g i c a l weed c o n t r o l measures w i l l have t o be implemented t o a s s u r e adequate f o o d and f i b e r p r o d u c t i o n . The q u a l i t y and q u a n t i t y o f f o o d and f i b e r p r o d u c t s w i l l no doubt d e c r e a s e and t h e i r c o s t s w i l l s o a r i f adequate a l t e r n a t i v e p e s t c o n t r o l measures have not been e s t a b l i s h e d and implemented. P e s t i c i d e s have been an I n t e g r a l p a r t o f commercial a g r i c u l t u r a l p r o d u c t i o n f o r so l o n g t h a t agroecosystems t h e m s e l v e s have been I n f l u e n c e d and, t h u s , e x t e n s i v e l o s s e s due t o p e s t s w i l l o c c u r i f t h e i r use 1s c u r t a i l e d ( l f l ) w i t h o u t new a l t e r n a t i v e s . Growth o f t h e I n t e r e s t i n a l t e r n a t i v e weed c o n t r o l methods has been brought about by t h e need f o r l e s s p e r s i s t e n t , more s e l e c t i v e , and more e n v i r o n m e n t a l l y s a f e h e r b i c i d e s . In my v i e w , i t becomes o b v i o u s t h a t improved weed c o n t r o l measures w i t h c h e m i c a l s a r e , and w i l l c o n t i n u e t o be an I n t e g r a l p a r t o f meeting t h e I n c r e a s i n g w o r l d demand f o r food and f i b e r . Furthermore, b i o l o g i c a l c o n t r o l o f a g r i c u l t u r a l p e s t s , p a r t i c u l a r l y weed c o n t r o l w i t h pathogens and m i c r o b i a l p r o d u c t s , can p l a y an i n c r e a s i n g r o l e i n meeting t h i s c h a l l e n g e . Research e f f o r t s i n academic, g o v e r n m e n t a l , and i n d u s t r i a l l a b o r t o r i e s must be expanded t o meet t h i s c h a l l e n g e . Weed C o n t r o l - Some H i s t o r i c a l P e r s p e c t i v e s . Weed c o n t r o l has gone t h r o u g h many s t a g e s s i n c e man gave up h i s nomadic h u n t e r - g a t h e r e r l i f e s t y l e t o form a g r a r i a n c o m m u n i t i e s . Few new developments i n weed c o n t r o l were made from t h o s e e a r l y days o f hand-weeding and c u l t i v a t i o n u n t i l t h e development o f s y n t h e t i c h e r b i c i d e s i n t h e mid 1 9 4 0 ' s . There a r e c u r r e n t l y about 150 h e r b i c i d e s c o m p r i s i n g about 15 major c h e m i c a l c l a s s e s r e g i s t e r e d f o r use i n t h e U n i t e d S t a t e s (II). B r i a n (12) has d e v e l o p e d a r e v i e w o f t h e h i s t o r y o f c h e m i c a l h e r b i c i d e s . A c h r o n o l o g y o f some weed c o n t r o l developments, w i t h p a r t i c u l a r emphasis on b i o l o g i c a l weed c o n t r o l , 1s p r e s e n t e d i n T a b l e I I I . W h i l e i t cannot t o t a l l y r e p l a c e c h e m i c a l s , b i o l o g i c a l c o n t r o l has l o n g been r e c o g n i z e d as a f e a s i b l e method o f weed control. However, i t has had a r a t h e r low p r o f i l e s i n c e t h e coming



HOAGLAND

An Overview

0

ι

1

1

1966

1971

1976

1

1981

1

1986

YEAR Fungicides

Herbicides — —

Insecticide

Figure 1. Estimates of pesticide usage in the United States, 1966-1987. (Redrawn from Ref. 7. Copyright 1989 National Academy Press.)

Herbicides

insecticides/Acaricides/ Nematicides (31.4%) Figure 2. Relative percentage of global pesticide sales for 1985. (Redrawn from Ref. 8. Copyright 1988 Royal Soc. London.)


6


Table III. Chronology of Some Important Events Related to Weed Control With Biocontrol Agents, and Microbial Products

Herbicides,


1859-87: Julius Sachs studied "chemical messengers" or growth regulators in plants 1896:

Bonnet observed a Bordeaux mixture killed charlock (Skiapsis arvensis L ) (12)

1900:

Charles Darwin published 'The Power of Movement in Plants"; studied plant movement relative to light and growth regulating substances in plants.

1901 :

H.L Bolley (U.S.) demonstrated weed control using inorganic salts. (12)

1902:

Introduction of various insects into Hawaii for control of L&ntBDA &UI1&E& L.

1925:

Eggs of Cactoblastis cactorum imported into Australia from Argentina for control of prickly pear cactus (Opuntia inermis and Q. strictal (14)

1931 :

Control of prickly pear cactus in Australia achieved by Cactoblastis cactorum.

1941 :

R. Pokomy (U.S.) reported chemical synthesis of 2,4-D (13

1942:

P.W. Zimmerman and A.E. Hitchcock (U.S.) reported 2,4-D to be a PGR (lfi)

1944:

P.C. Marth and J.W. Mitchell (U.S.) established selectivity of 2,4-D (ID C.L Hamner and H.B. Tukey (U.S.) used 2,4-D in field weed control (IS)

1945:

W.G. Templeman (U.K.) established principle of preemergence soil herbicides

1951 :

JAtefidS, journal of the Assoc. of Regional Weed Contr. Conferences, established

1954:

Role of diseases in weed control recognized (IS)

1956:

Weed Science Society of America organized; assumed publication of WfifidS renamed Weed Science in 1968

1961 :

Sflififid Research, journal of the European Weed Research Council, published

1968:

Principles of Plant and Animal Pest Control. Vol. 2: Weed Control (publication 1597) published by the National Academy of Sciences, confirming the importance of weed science, including biological control, as a discipline

1969:

Discovery of endemic disease, Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. aeschvnomeme on the weed jointvetch [Aeschvnomene yjrajoiia (L.) B.S.P.] (20)

1970:

International Conference of Weed Control organized by the FAO of the United Nations; showed international concern for world weed problems

1971 :

Successful establishment of Puccinia chondrilla against rush skeletonweed fChondrilla juncea) and skeletonweed [Lygodesmia juncea (Pursh.) D. Don] (21)

1973:

First successful use of augmentative biocontrol of northern jointvetch (22)

1976:

International Weed Science Society formed

1979: 1981 :

First microbial herbicide (bialaphos) patented (23) DEVINE, a formulation of Phvtophthora paimivora (Butier) Butler, registered for use against stranglervine (Morrenia odorata Undl.) in citrus (24)

1982:

Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. aeschvnomene registered as COLLEGO, a formulation for selective control of northern jointvetch (2D

1989:

Microbial Strain selection for bialaphos production resulted in 500-fold increase above wild type (23



1.

HOAGLAND

7

An Overview

o f s y n t h e t i c c h e m i c a l h e r b i c i d e s b e g i n n i n g i n t h e 1 9 4 0 ' s . Host weed b i o c o n t r o l s u c c e s s e s have I n v o l v e d t h e use o f I n t r o d u c e d phytophagous I n s e c t s . The use o f p l a n t pathogens and t h e i r p h y t o t o x i n s 1s a r a t h e r new a p p r o a c h . A l t h o u g h p l a n t d i s e a s e s have been r e c o g n i z e d and have I n t r i g u e d f a r m e r s and r e s e a r c h e r s f o r y e a r s , t h e r e have been few attempts t o f o r m a l l y a p p l y the concept o f t h e s e l e c t i v e use o f d i s e a s e s f o r weed c o n t r o l . A landmark example o f t h e use o f t h e c l a s s i c a l b i o l o g i c a l c o n t r o l approach ( i . e . , i n t r o d u c t i o n o f an e x o t i c organism t o c o n t r o l an I n t r o d u c e d p e s t ) f o r a weed problem was t h e e s t a b l i s h m e n t o f Puceinn1a c h o n d r i l l a Bubak. and S y d . f o r c o n t r o l o f r u s h skeletonweed ( C h o n d r i l l a i u n c e a l and skeletonweed fLvaodesmia j u n c e a ( P u r s h . ) D. Don] i n A u s t r a l i a i n 1971 (21). The f i r s t weed c o n t r o l s u c c e s s u s i n g t h e augmentative b i o c o n t r o l approach ( i . e . , I n u n d a t i v e r e l e a s e s o f l a r g e numbers o f Indigenous b i o l o g i c a l c o n t r o l agents t o a c h i e v e c o n t r o l o f a p e s t ) was t h e use o f C o l l e t o t r i c h u m a l o e o s p o r i o d e s ( P e n z . ) S a c c . f . s p . aeschvnomene a g a i n s t n o r t h e r n j o i n t v e t c h ΓAeschvnomene v i r o i n i c a ( L . ) B . S . P . ] i n 1973 (22). Much r e s e a r c h has been done i n t h e a r e a o f b i o l o g i c a l c o n t r o l o f weeds w i t h p l a n t pathogens s i n c e t h e s e i n i t i a l s u c c e s s e s . However, what i s needed t o I d e n t i f y and e s t a b l i s h a new i n d i v i d u a l s u c c e s s f u l b i o c o n t r o l c a n d i d a t e remains l a r g e l y unknown. In my v i e w , a r a t i o n a l and e n v i r o n m e n t a l l y b e n e f i c i a l approach t o t h e weed c o n t r o l problem i s i n t e g r a t e d c o n t r o l ; I . e . , u s i n g s y n t h e t i c c h e m i c a l s , phytophagous i n s e c t s , and p l a n t pathogens (S, 21» 2Ê-2Z) a n d / o r c h e m i c a l s d e r i v e d from p l a n t s and m i c r o b e s (23-2Â). The purpose o f t h i s symposium was t o a s s e s s r e c e n t p r o g r e s s and p r o s p e c t s i n v a r i o u s areas r e l a t i n g t o p l a n t pathogens t h a t a t t a c k weeds and novel p h y t o t o x i c c h e m i s t r i e s from m i c r o o r g a n i s m s . The scope o f t h i s book i s t h e c o n t r o l o f weeds u s i n g microbes and m i c r o b i a l p r o d u c t s . T h i s o v e r v i e w c h a p t e r touches on some o f t h e s e a r e a s , w i t h t h e major f o c u s on t h e c h e m i s t r i e s o f p h y t o t o x i n s produced by p l a n t pathogens and o t h e r m i c r o o r g a n i s m s . D i s c o v e r y and S c r e e n i n g o f S y n t h e t i c H e r b i c i d e s . H e r b i c i d e s , and M i c r o b i a l P h y t o t o x i n s

Microbial

S y n t h e t i c H e r b i c i d e s . Most commercial p h y t o t o x i n s ( h e r b i c i d e s ) have been d i s c o v e r e d through random s c r e e n i n g programs, f o l l o w e d by d e r i v a t i v e s y n t h e s i s and a c t i v i t y s t u d i e s when a p o t e n t i a l c h e m i c a l c a n d i d a t e i s d i s c o v e r e d . Seldom has a b i o r a t i o n a l approach f o r h e r b i c i d e d i s c o v e r y been a c h i e v e d o r u s e d . Over t h e p a s t 45-50 y e a r s , perhaps c l o s e t o a m i l l i o n compounds have been screened f o r h e r b i c i d a l a c t i v i t y . The number o f compounds s c r e e n e d has c o n t i n u a l l y i n c r e a s e d and e s t i m a t e s f o r the 1980's suggest t h a t 12 t o 15 thousand compounds per y e a r were s y n t h e s i z e d and screened f o r each compound r e a c h i n g t h e market (2S). In the 1 9 9 0 ' s , t h e r a t i o may i n c r e a s e 5 - f o l d . Such s c r e e n i n g o f s y n t h e t i c compounds t y p i c a l l y I n v o l v e s greenhouse t e s t i n g o f up t o a dozen o r so i m p o r t a n t c r o p and weed s p e c i e s f o r both pre-emergence and post-emergence a c t i v i t y . S t r a t e g y may be changing somewhat i n t h a t i n h i b i t i o n o f s p e c i f i c t a r g e t s i n p l a n t s i s a l s o b e i n g c o n s i d e r e d i n o r d e r t o improve chances o f d i s c o v e r i n g p o t e n t h e r b i c i d e s t h a t have minimal e f f e c t t o n o n - t a r g e t s i t e s , e s p e c i a l l y t h o s e i n mammals and o t h e r v e r t e b r a t e


8



s p e c i e s . S i m p l e model s p e c i e s , c e l l f r e e a s s a y s , and s p e c i f i c enzyme a s s a y s may p r o v i d e a d d i t i o n a l advantages I n such s c r e e n i n g programs (31). Pathogens. The d i s c o v e r y o f l i v i n g organisms f o r use as b i o h e r b i c i d e s 1s c o n s i d e r a b l y more complex than t h e d i s c o v e r y o f s y n t h e t i c p h y t o t o x i n s . " B i o h e r b i c l d e , " as used h e r e , r e f e r s t o microorganisms ( f u n g i , b a c t e r i a , v i r u s e s , algae, e t c . ) o r t h e i r p r o d u c t s t h a t have been used o r have p o t e n t i a l f o r use 1n t h e augmentative c o n t r o l o f weedy s p e c i e s . " M y c o h e r b l d d e " has r e q u e n t l y been used 1n t h e l i t e r a t u r e t o d e s c r i b e t h e d i r e c t use o f p a t h o g e n i c f u n g a l organisms f o r weed c o n t r o l . Pathogens f o r weed c o n t r o l r e p r e s e n t unique m i c r o b e : p i ant a s s o c i a t i o n s . Generally, d i s e a s e d p l a n t s a r e d i s c o v e r e d i n t h e f i e l d o r greenhouse and t h e p r o c e s s o f I s o l a t i n g and I d e n t i f y i n g t h e c a u s a l agent b e g i n s . The f i r s t s t e p 1s t o I s o l a t e t h e s u s p e c t pathogen and grow 1 t i n pure c u l t u r e , as d e s c r i b e d by s p e c i f i c p l a n t p a t h o l o g i c a l t e c h n i q u e s (32, 33)· Organism I d e n t i f i c a t i o n 1s an Important second s t e p . A r e f e r e n c e which i s t h e usual s t a r t i n g p o i n t f o r i n f o r m a t i o n on p l a n t d i s e a s e s 1n t h e U . S . 1s The Index o f P l a n t D i s e a s e s i n t h e U n i t e d S t a t e s , which g i v e s i n f o r m a t i o n on pathogen h o s t - r a n g e and d i s t r i b u t i o n (34-25). S e v e r a l o t h e r s p e c i f i c s t a t e and f o r e i g n I n d i c e s have been c o m p i l e d , as summarized by Tempieton e t a l . (2Ζ)· L i s t i n g s o f f u n g a l d i s e a s e s , encompassing t h e e n t i r e w o r l d l i t e r a t u r e , a r e a l s o a v a i l a b l e (38-11). The n e x t p r o c e s s I s e s s e n t i a l l y p r o v i n g t h a t t h e I s o l a t e d and I d e n t i f i e d o r g a n i s m 1s indeed t h e d i s e a s e - c a u s i n g a g e n t . T h i s 1s a c c o m p l i s h e d u t i l i z i n g K o c h ' s P o s t u l a t e s , I . e . , t h e pathogen must always b e : found a s s o c i a t e d w i t h a p a r t i c u l a r d i s e a s e symptom o f t h e weed; I s o l a t e d In pure c u l t u r e ; used t o I n o c u l a t e and Induce d i s e a s e c h a r a c t e r i s t i c s 1n h e a l t h y weed t i s s u e ; r e i s o l a t e d from t h e I n o c u l a t e d weed and t h e d i s e a s e symptoms and r e c o v e r e d pathogen compared p o s i t i v e l y w i t h t h e o r i g i n a l d i s e a s e symptoms and m i c r o o r g a n i s m . S e v e r a l c y c l e s o f K o c h ' s P o s t u l a t e s p r o v i d e an i n d i c a t i o n o f f a c t o r s such as v i r u l e n c e , s t a b i l i t y , and e n v i r o n m e n t a l r e q u i r e m e n t s f o r g r o w t h , s p o r u l a t i o n , i n f e c t i o n s , and d i s e a s e develoment, which a r e a l l Important a s p e c t s f o r a s s e s s i n g t h e p o t e n t i a l o f t h e organism as a b i o h e r b i c i d e . As w i t h s y n t h e t i c h e r b i c i d e s , i t 1s Important t h a t b i o h e r b i c i d e s have p h y t o t o x i c s p e c i f i c i t y w i t h minimal impact on n o n - t a r g e t o r g a n i s m s . However, a b r o a d e r h o s t range would be v e r y b e n e f i c i a l and make a p a r t i c u l a r o r g a n i s m more a t t r a c t i v e c o m m e r c i a l l y . With pathogens, h o s t - r a n g e t e s t s o f t h e organism a r e conducted p r i o r t o f i e l d t e s t i n g (42, 13) u s i n g o p t i m a l d i s e a s e - d e v e l o p m e n t environments and both s u s c e p t i b l e and r e s i s t a n t p l a n t s , I n c l u d i n g a l l known b i o t y p e s o f t h e h o s t and o t h e r p l a n t s c l o s e l y r e l a t e d b o t a n i c a l l y t o t h e known h o s t (43, Μ ) · Even i f p r e l i m i n a r y t e s t s show a pathogen t o have a d e s i r a b l e h o s t r a n g e , s c r u t i n y o f t h e epidemiology i s a n e c e s s a r y / c r i t i c a l f a c t o r i n determining the p o t e n t i a l f o r f u r t h e r development as a b i o h e r b i c l d e . O t h e r c r i t e r i a are important f o r successful commercialization o f t h e b i o h e r b i c l d e c a n d i d a t e s . These i n c l u d e inoculum p r o d u c t i o n , p a c k a g i n g and s h e l f - l i f e , and v a r i o u s a s p e c t s o f a p p l i c a t i o n t e c h n o l o g y . A f i n a l Important c r i t e r i o n f o r t h e commercial development o f a pathogen i s i t s i n t e r a c t i o n and c o m p a t a b i l i t y w i t h o t h e r a g r o c h e m i c a l s .



1.

HOAGLAND

An Overview

9

P h y t o t o x i n s from M i c r o b e s as H e r b i c i d e s . The concept here i s t o use p h y t o t o x i n s e i t h e r as h e r b i c i d e s t h e m s e l v e s o r t o broaden t h e h o s t s p e c i f i c i t y beyond t h a t I n h e r e n t i n t h e o r g a n i s m , t h u s u l i t i z i n g n o n - s e l e c t i v e t o x i n s on o t h e r non-host weeds. C o - e v o l u t i o n o f t o x i n - p r o d u c i n g pathogens w i t h t h e i r s p e c i f i c p l a n t h o s t s p e c i e s has r e s u l t e d i n the production of h o s t - s p e c i f i c t o x i n s , I . e . , t o x i n s t h a t o n l y a f f e c t t h e s p e c i e s i n f e c t e d by t h e p a t h o g e n . Most known h o s t - s p e c i f i c p h y t o t o x i n s have been c h a r a c t e r i z e d from c r o p pathogens, w h i l e s t u d i e s on h o s t - s p e c i f i c p h y t o t o x i n s from weed pathogens have been n e g l e c t e d . I s o l a t i o n and c h e m i c a l c h a r a c t e r i z a t i o n o f h o s t - s p e c i f i c and n o n - s p e c i f i c p h y t o t o x i n s from pathogens and non-pathogens may p r o v i d e t e m p l a t e s f o r a n a l o g s y n t h e s i s t o d e v e l o p h e r b i c i d e s w i t h even more d e s i r a b l e c h a r a c t e r i s t i c s than some s y n t h e t i c compounds p r e s e n t l y m a r k e t e d . A l t h o u g h p a t h o g e n i c organisms may be t h e f i r s t t o come t o mind when d i s c u s s i n g p h y t o t o x i n - p r o d u c i n g agents as b i o h e r b i c i d e s , many n o n - p a t h o g e n i c o r g a n i s m s , i n c l u d i n g b a c t e r i a and f u n g i , a l s o p o s s e s s / p r o d u c e p h y t o t o x i c compounds. Indeed, some o f t h e a n t i b i o t i c s i s o l a t e d from n o n - p l a n t pathogens have been l a t e r shown t o p o s s e s s h i g h l y p o t e n t p h y t o t o x i c p r o p e r t i e s . Some p r o g r e s s has been made i n t h e areas o f i s o l a t i o n and s c r e e n i n g o f p h y t o t o x i n s as h e r b i c i d e s , as e v i d e n c e d i n s e v e r a l r e c e n t r e v i e w s (2fl, 45-51). S c r e e n i n g o f compounds produced by s o i l m i c r o o r g a n i s m s has a l s o r e s u l t e d i n t h e d i s c o v e r y o f b l o h e r b l c i d e s (52*54). G e n e r a l l y , most o f t h e s e compounds have not been e x t e n s i v e l y t e s t e d as t o weed specificity. I t i s o b v i o u s t h a t t h e s e organisms produce many y e t u n i d e n t i f i e d compounds t h a t a l s o may have p o t e n t i a l f o r development as bloherblcides. Several f a c t o r s determine the extent of the development p r o c e s s . F i r s t i s t h e need f o r a means t o produce adequate amounts o f t h e m i c r o o r g a n i s m s f o r t e s t i n g . Second 1s an adequate and a p p r o p r i a t e p l a n t b l o a s s a y s y s t e m . C u l t u r a l c o n d i t i o n s can i n f l u e n c e t h e m e t a b o l i t e s produced by a g i v e n o r g a n i s m , e i t h e r pathogenic or non-pathogenic. With a pathogen, t h e h o s t ( s ) i s known and t e s t s f o r v i r u l e n c e can be c o n d u c t e d . Indeed, t h e o r g a n i s m can and s h o u l d be produced u t i l i z i n g e x t r a c t s o r p l a n t p a r t s o f t h e n a t u r a l h o s t ( s ) i n o r d e r t o m a i n t a i n v i r u l e n c e . The h o s t ( s ) s h o u l d be among t h e b l o a s s a y t e s t p l a n t s . B i o a s s a v . The a b i l i t y t o f o l l o w p h y t o t o x i c symptoms caused by organisms o r i s o l a t e d p h y t o t o x i n s t h r o u g h o u t p u r i f i c a t i o n and p r o d u c t i o n p r o c e s s e s i s o f paramount Importance. A problem common t o t e s t i n g o f p h y t o t o x i n s from both pathogens and non-pathogens i s t h e l i m i t e d amount o f m a t e r i a l a v a i l a b l e , which s e v e r l y r e s t r i c t s t h e number, s i z e , e t c . o f p l a n t s p e c i e s t h a t can be used i n b l o a s s a y o r s c r e e n i n g t e s t s . S y n t h e t i c h e r b i c i d e compounds a r e not s u b j e c t t o t h i s l i m i t a t i o n . The problem can be compounded f o r n o n - p a t h o g e n i c s p e c i e s . For example, s i n c e t h e r e i s a v a r i e t y o f s y n t h e t i c media a v a i l a b l e , i t 1s I m p o s s i b l e t o e a s i l y o p t i m i z e f o r p h y t o t o x i n p r o d u c t i o n w i t h o u t t e s t i n g a range o f media and v a r i o u s culture conditions. S e v e r a l b i o a s s y t e c h n i q u e s have been d e v e l o p e d which a l l o w t e s t i n g o f b i o l o g i c a l m a t e r i a l s produced i n s m a l l q u a n t i t i e s . The e x c i s e d wheat c o l e o p t i l e t e s t (55) has v e r s a t i l i t y i n d e t e c t i n g p l a n t growth promoters and and growth i n h i b i t o r s . The assay i s



10


s i m p l e and q u i c k . The duckweed (Lemna s p . ) b l o a s s a y system (56, 5Z) has some a d d i t i o n a l a d v a n t a g e s . An i n t a c t p l a n t system i s u s e d ; growth and c h l o r o p h y l l c o n t e n t can be measured as w e l l as p r o c e s s e s l i k e r e s p i r a t i o n and p h o t o s y n t h e s i s . A s s a y s t h a t do not d e t e c t light-dependent processes are l i m i t i n g . A l e t t u c e seed/seedling b l o a s s a y (Ifi) has been u s e f u l i n d e t e c t i n g t h e e f f e c t s o f r e l a t i v e l y s m a l l amounts o f t o x i n on growth and g e r m i n a t i o n . A n o t h e r b l o a s s a y f o r t h e s e purposes uses e x c i s e d o a t m e s o c o t y l s (£8). Other reviews have s u r v e y e d s c r e e n i n g p r o c e d u r e s and b i o a s s a y s o f p h y t o t o x i n s from m i c r o b e s (5Q, 52). B i o a s s a y s t h a t have been used f o r s p e c i f i c h e r b i c i d e s , t h e d e t e c t i o n o f p h o t o s y n t h e s i s i n h i b i t o r s , and t h e use o f m i c r o b e s as b l o a s s a y s u b j e c t s have been summarized (fifi). Various p l a n t growth r e g u l a t o r b i o a s s a y s have been r e v i e w e d ( i l ) , but a s s a y s t h a t d e t e c t o n l y PGR a c t i v i t y may not be u s e f u l f o r b i o h e r b i c l d e s c r e e n i n g . G e n e r a l l y , a l l o f t h e above a s s a y s a r e s p e c i e s - s p e c i f i c and, t h u s , many compounds w i t h p o t e n t i a l p h y t o t o x i c i t i e s a r e m i s s e d . C e l l f r e e a s s a y s a n d / o r s p e c i f i c enzyme t e s t i n g (11) c o u p l e d w i t h i n t a c t t i s s u e a s s a y s s h o u l d have u t i l i t y f o r s c r e e n i n g t h e r e l a t i v e l y s m a l l amounts o f p h y t o t o x i n s produced by m i c r o b e s . A a r o c h e m i c a l I n t e r a c t i o n s w i t h Pathogens. C u r r e n t l y t h e r e i s o n l y s p a r s e I n f o r m a t i o n on i n t e r a c t i o n s o f b l o h e r b l c i d e s w i t h s y n t h e t i c p e s t i c i d e s ( f u n g i c i d e s , i n s e c t i c i d e s , and h e r b i c i d e s ) . Such I n t e r a c t i o n s can be e i t h e r a n t a g o n i s t i c o r s y n e r g i s t i c w i t h t h e b i o l o g i c a l a c t i v i t y of the b i o h e r b i c l d e . Some h e r b i c i d e s have been shown t o a c t s y n e r g i s t i c a l l y w i t h v a r i o u s pathogens t o I n c r e a s e v a r i o u s s o i l - b o r n e r o o t d i s e a s e s [èl). Such i n t e r a c t i o n s , c o u p l e d w i t h a b i o h e r b i c i d e , may o f f e r unique weed c o n t r o l p o t e n t i a l s . A n o t h e r a s p e c t o f such i n t e g r a t e d c o n t r o l 1s t h e a p p l i c a t i o n o f more t h a n one b i o h e r b i c l d e t o c o n t r o l more than one weed, e s p e c i a l l y i n c a s e s where an i n d i v i d u a l o r g a n i s m i s r e l a t i v e l y s p e c i f i c . An example o f t h i s i s t h e use o f COLLEGO and C o l l e t o t r i c h u m q l o e o s p o r l o d e s ( P e n z . ) S a c c . f . i u s s i a e f o r c o n t r o l o f winged w a t e r p r i m r o s e f L u d w i a i a d e c u r r e n s ( W a l t . ) ] and n o r t h e r n j o i n t v e t c h i n r i c e ( 6 1 ) . COLLEGO has perhaps been more r i g o r o u s l y t e s t e d f o r i n t e r a c t i o n s w i t h v a r i o u s p e s t i c i d e s than have o t h e r b l o h e r b l c i d e s o r p o t e n t i a l b i o h e r b i c i d e s . The s y n t h e t i c h e r b i c i d e s p r o p a n i l [ M - ( 3 , 4 - d i c h l o r o p h e n y l ) p r o p a n a m i d e ] and 2 , 4 , 5 - T [ 2 - ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) a c e t i c a c i d ] , a p p l i e d a f t e r COLLEGO t r e a t m e n t i n r i c e , d i d not i n h i b i t d i s e a s e I n f e c t i o n and development. Some i n s e c t i c i d e s and t h e h e r b i c i d e s a c i f l u o r f e n { 5 - [ 2 - c h l o r o - 4 - ( t r 1 f1uoromethy1) p h e n o x y ] - 2 - n i t r o b e n z o i c a d d } and bentazon [ 3 - ( l methylethyl)-(lH)-2,l,3-benzothiadiaz1n-4(3H)-one 2,2-dioxide], a p p l i e d i n t a n k m i x t u r e o r s e q u e n t i a l t r e a t m e n t s w i t h COLLEGO, d i d not i n h i b i t d i s e a s e i n f e c t i o n o r development on n o r t h e r n j o i n t v e t c h ( 6 4 ) . A n o t h e r p o s i t i v e i n t e r a c t i o n has been demonstrated u s i n g t a n k mix c o m b i n a t i o n s o f t h e fungus C o l l e t o t r i c h u m coccodes and t h e p l a n t growth r e g u l a t o r t h i d l a z u r o n ( M - p h e n y l - M ' - l , 2 , 3 - t h 1 d i a z o l - 5 - y l - u r e a ) t o i n c r e a s e v e l v e t l e a f (Abut11 on t h e o p h r a s t i ) m o r t a l i t y and i n c r e a s e soybean ( G l y c i n e max) y i e l d s ( 5 5 ) . Important s y n e r g i s t i c i n t e r a c t i o n s o f h e r b i c i d e s o r p l a n t growth r e g u l a t o r s c o u l d reduce t h e amount o f both s y n t h e t i c agrochemical and b i o l o g i c a l inoculum needed t o c o n t r o l s p e c i f i c weed p r o b l e m s . More r e s e a r c h i n p u t i s needed i n t h e s e a r e a s .


1.

HOAGLAND

An Overview

11

P h y t o t o x i c Compounds Produced bv M i c r o o r g a n i s m s Many new m i c r o b i a l compounds w i t h p o t e n t i a l b i o c h e r b i c i d a l a c t i v i t y have been i s o l a t e d , c h e m i c a l l y c h a r a c t e r i z e d , and a p o r t i o n o f t h e i r b i o l o g i c a l a c t i v i t i e s determined u s i n g v a r i o u s b l o a s s a y t e c h n i q u e s o r by d i r e c t p l a n t s c r e e n i n g . Some o f t h e s e compounds a r e v i r u l e n c e f a c t o r s o f p l a n t pathogens, thus i n f o r m a t i o n on t h e s e p h y t o t o x i n s can b e n e f i t t h e development o f microbes as h e r b i c i d e s and p o t e n t i a l l y p r o v i d e new chemical h e r b i c i d e s . Data on some o f t h e s e compounds and t h e i r s t r u c t u r e s are p r e s e n t e d . I n f o r m a t i o n on s o u r c e , b i o l o g i c a l a c t i v i t y , and p o s s i b l e mode o f a c t i o n (when a v a i l a b l e ) i s b r i e f l y summarized.


P h y t o t o x i c Compounds Produced by Fungal Weed Pathogens C u r v u l i n s . C u r v u l i n [ 1 ] , a c y c l i c p o l y k e t i d e , and O - m e t h y l c u r v u l i n i c a c i d [2] were f i r s t i d e n t i f i e d i n t h e l a t e 1 9 6 0 ' s . A l t h o u g h c u r v u l i n i s produced by many f u n g i , i t s b i o l o g i c a l a c t i v i t y was then unknown (££). Both compounds were r e c e n t l y i s o l a t e d from D r e s c h s l e r a i n d i c a . a pathogen o f two weed s p e c i e s , s p i n y amaranth (Amaranthus s p i n o s u s L.) and common p u r s l a n e ( P o r t u l a c a o l e r a c e a L . ) , and i t s s t r u c t u r e c o n f i r m e d u s i n g x - r a y c r y s t a l l o g r a p h y ( 6 Z ) . The compounds were p h y t o t o x i c t o detached l e a v e s o f t h e s e h o s t p l a n t s , but some o t h e r p l a n t s were not i n j u r e d . D r e c h s l e r a s i c c a n s i s a f u n g a l pathogen on p e r e n n i a l r y e g r a s s ( L o i 1 urn oerenne L . ) , I t a l i a n r y e g r a s s ( L . m u l t i f l o r i u m L a m . ) , and o a t (£8). R e c e n t l y d e - O - m e t h y l d i a p o r t h i n [3] was i s o l a t e d from t h i s fungus, s t r u c t u r a l l y c h a r a c t e r i z e d , and shown t o be p h y t o t o x i c . Host p l a n t s , however, showed l i t t l e o r no s e n s i t i v i t y t o t h i s compound w h i l e soybean, c o r n , c r a b g r a s s were s e n s i t i v e t o 4 nmol a p p l i e d i n 3 μΐ d r o p l e t s . S p i n y amaranth and b a r n y a r d g r a s s were more t o l e r a n t and r e q u i r e d 12 and 8 nmol/3 μΊ d r o p l e t , r e p e c t i v e l y , t o cause i n j u r y . E r e m o p h i l a n e s . Many eremophilanes have been i s o l a t e d from f u n g i . The f i r s t eremophilane compounds t h a t e x h i b i t e d p h y t o t o x i c a c t i v i t y were i s o l a t e d from B i p o l a r i s c v n o d o n t i s . a pathogen o f bermudagrass rCvnodon d a c t y l on ( L . ) P e r s . ] (SS). T h i s f u n g a l pathogen produces two e r e m o p h i l a n e s , b i p o l a r o x i n [4] and d i h y d r o b i p o l a r o x i n (reduced a n a l o g o f b i p o l a r o x i n ) . T h i s reduced a n a l o g , l a c k i n g t h e aldehyde m o i e t y , i s not p h y t o t o x i c , but b i p o l a r o x i n causes l e s i o n s on bermudagrass l e a v e s a t c o n c e n t r a t i o n s o f 38 μΜ. Higher c o n c e n t r a t i o n s a r e n e c e s s a r y t o i n j u r e w i l d o a t s (Avena f a t u a L . ) , c o r n , and sugarcane (Saccharum o f f i c i n a r u m L . ) . O r g a n i c e x t r a c t i o n and a n a l y s i s o f c u l t u r e f i l t r a t e s o f D r e c h s l e r a g j g a n t e a . a pathogen o f q u a c k g r a s s rAgroovron reoens ( L . ) B e a u v . ] and bermudagrass, showed o v e r a dozen e r e m o p h i l a n e s were produced (54)· Phomenone, p e t a s o l [ 5 ] , and g i g a n t e n o n e [6] caused n e c r o t i c symptoms on d i c o t y l e d o n o u s p l a n t t i s s u e , but on monocotyledons caused l o c a l i z e d r e t e n t i o n o f c h l o r o p h y l l ("green i s l a n d s " ) (54)· Cucumber (Cucumis s a t i v u s L.) was an e x c e p t i o n , s i n c e "green i s l a n d s " a l s o formed i n t h i s d i c o t y l e d o n . Various pathogens ( 7 0 , Z l ) had been known t o cause "green i s l a n d s " , an e f f e c t a l s o caused by l o c a l i z e d a p p l i c a t i o n o f c y t o k i n i n s t o y e l l o w i n g ( s e n e s c i n g ) l e a v e s (Z2). Z i n n i o l [13] (ZS) and some


12



Curvulin [1 ]

Mono-O-methyt-

D e ^ m e t h y k t e p o r t M n [3]

curvulinicadd[2]

Bipolaroxin [4]

Maculosin [7]

Petasol [5]

H

3

C

Giganlenone [6]

w

OphiobolinA[8]


1.

HOAGLAND

An Overview

13

polyhydroxamates ( H ) a r e o t h e r compounds produced by p l a n t pathogens t h a t cause t h e "green I s l a n d " e f f e c t . P R - t o x i n , a n o t h e r e r e m o p h i 1 i n e , 1s produced by P é n i c i l l i u m r o o u e f o r t 1 Thorn. (75). Phomenone has been I s o l a t e d from Phoma d e s t r u c t l v a P l o w r . , a fungus c a u s i n g w i l t d i s e a s e i n tomato f L v c o p e r s l c o n esculentum M i l l . ) (Z5). Phomenone, P R - t o x 1 n , and f o u r d e r i v a t i e s o f phomenone were assayed f o r p h y t o t o x i c a c t i v i t y 1n tomato s e e d l i n g s and c u t t i n g s (ZZ). Phomenone, acetylphomenone, and P R - t o x i n a t 1 0 ~ M caused w i l t i n g and n e c r o s i s and h a l v e d t h e growth r a t e o f s h o o t s and c o m p l e t e l y I n h i b i t e d t h e growth o f r o o t s . Phomenone 1s a l s o produced by t h e fungus Phoma e x i a u a (Z8). Gigantenone and p e t a s o l a l s o s t i m u l a t e a u x i n - l i k e a c t i v i t y by promoting r o o t f o r m a t i o n 1n mung bean r v i a n a radiâta ( L . ) W l l c z e k ] c u t t i n g s and r o o t i n g o f c a l 1 1 i n t i s s u e c u l t u r e o f s u n f l o w e r i H e l l a n t h u s annuus L ] (51). T h i s e f f e c t was absent i n t h e monocot asparagus (Asparagus o f f i c i n a l i s L ) , but t h e s e e r e m o p h i l a n e s caused l a r g e r and more branched asparagus s h o o t s .


4

M a c u l o s i n s . These compounds were I s o l a t e d from an A l t e r n a r l a a l t e r n a t a i n f e c t i o n on s p o t t e d knapweed (Centaurea maculosa Lam.) (Z2). A l t h o u g h many m a c u l o s i n s were I d e n t i f i e d , o n l y one compound, m a c u l o s i n - 1 [ 7 ] o r c y c l o l - p r o l i n e - L - t y r o s 1 n e , was found t o be a h o s t - s p e c i f i c p h y t o t o x i n o f s p o t t e d knapweed a t 10 μΜ. N i n e t e e n o t h e r g r a s s e s and b r o a d l e a v e d p l a n t s were n o t I n j u r e d by m a c u l o s i n - 1 , even a t c o n c e n t r a t i o n s o f 1 mH. T h i s compound, r e t a i n i n g host s p e c i f i c i t y o f t h e n a t u r a l l y o c c u r r i n g p r o d u c t , has r e c e n t l y been s y n t h e s i z e d from a methyl e s t e r o f L - t y r o s i n e and t-B0C-L-prol1ne (Sfi). OohloboHns. O p h i o b o l i n A [8] was t h e f i r s t member o f t h i s group t o be i d e n t i f i e d and I s a l s o t h e group member most s t u d i e d . Over 20 a n a l o g s have been I d e n t i f i e d . Most o f t h e s e compounds have been d e r i v e d from s e v e r a l pathogens o f t h e D r e c h s l e r a s p p . O p h i o b o l i n A was f i r s t I s o l a t e d from D r e c h s l e r a o r v z a e . a p a t h o g e n i c o r g a n i s m r e s p o n s i b l e f o r a major e p i d e m i c i n r i c e (51). T h i s compound has numerous e f f e c t s on r i c e (81)· Q- mavdis was t h e pathogen t h a t caused widespread c o r n l e a f b l i g h t ( S i ) and t h i s o r g a n i s m a l s o produces o p h i o b o l i n A and a t l e a s t f i v e o t h e r s i m i l a r a n a l o g s , i n c l u d i n g 6 - e p i o p h i o b o l i n A and 3 - a n h y d r o - 6 - e p i o p h 1 o b o l i n . These t h r e e compounds, p l u s 3 - a n h y d r o o p h i o b o l 1 n , have r e c e n t l y been i s o l a t e d from Q. s o r o h l c o l a - B i p o l a r i s s o r o h l c o l a . a f u n g a l pathogen o f j o h n s o n g r a s s iSorqhum hapeoense ( L . ) P e r s . ] ( S I ) - Four o p h i o b o l i n s were t e s t e d i n a l e a f - s p o t assay i n sorghum, s i c k l e p o d (Cassia QbtUSlfQTIfl L . ) , morning g l o r y [IPQWQM PMrPMrM ( L . ) R o t h ] , m a i z e , and b e n t g r a s s ( A a r o s t i s a l b a L.) O p h i o b o l i n A and 6 - e p i o p h i o b o l i n A were more p h y t o t o x i c than t h e i r anhydro- c o u n t e r p a r t s a g a i n s t sorghum, s i c k l e o o d , and maize (£1). O p h i o b o l i n A a t low c o n c e n t r a t i o n s (5 x 1 0 ' t o 7.5 χ 10 "° M) d i s r u p t e d membrane p o t e n t i a l and caused l e a k a g e and potasium i o n e f f l u x . Calmodulin f u n c t i o n i s d i s r u p t e d by t h i s compound (34)· D- mavdis r a c e Τ produced 6 - e p i o p h i o b o l i n A and 3 - a n h y d r o - 6 - e p i o p h i o b o l i n A, which s p e c i f i c a l l y i n h i b i t e d malate o x i d a t i o n i n a mitochondrial e l e c t r o n t r a n s p o r t assay from T e x a s - m a l e - s t e r i l e (TMS) c o r n (85). Q- mavdis r a c e 0 d i d n o t produce t h e s e 2 p h y t o t o x i n s . However, i t was p h y t o t o x i c t o c o r n and not s p e c i f i c t o TMS c o r n . O p h i o b o l i n G and H have been I s o l a t e d from A s p e r g i l l u s u s t u s (25)· 5


14


P e r v l e n e a u i n o n e s . A l t e r n a r i a e i c h o r n i a e . a pathogen o f w a t e r h y a c i n t h r E i c h o r n i a c r a s s i p e s ( M a r t . ) S o l m s ] , produces a p h y t o t o x i n , a l t e i c h i n [ 9 ] , which causes n e c r o t i c l e s i o n s analogous t o t h e pathogen i n f e c t i o n when t h e compound i s a p p l i e d a t 1-10 jxg/lO μΐ d r o p l e t (8Z). The pathogen Stemphvlium botvosum v a r . l a c t u c u m i s t h e c a u s a l agent o f l e a f s p o t on l e t t u c e . I t produces s t e m p h y p e r y l e n o l [10] and s t e m p h y l t o x i n s [11] I (Ri - H, R and R - OH, R - H o ) , I I ( R i « H, Rp OH, R and - H o ) , I I I (R - R, R - O A , R anâ R H ) , and IV ( R j - H , Ro - OH, carbons a t R and R 4 j o i n e d i n e p o x i d e l i n k a g e ) which a r e a n a l o g s o f a l t e i c h i n (88). 2

3

4

}

3

2

3

4


3

T r v p t o p h o l . T r y p t o p h o l [12] i s a n a t u r a l p r o d u c t i n p l a n t s and m i c r o o r g a n i s m s and i s I n v o l v e d i n i n d o l e a c e t i c a d d m e t a b o l i s m . A major m e t a b o l i t e from D r e c h s l e r a nodulosum. t r y p t o p h o l was i s o l a t e d and i d e n t i f i e d from e x t r a c t s o f c u l t u r e f i l t r a t e s o f t h i s f u n g a l pathogen (82). T h i s r e p o r t was t h e f i r s t t o show t h a t t h i s compound was p h y t o t o x i c and caused n e c r o t i c l e s i o n s on g o o s e g r a s s ( E l e u s i n e i n d i c a L . ) , t h e weed host o f t h i s f u n g u s . N e c r o t i c i n j u r y i n . g o o s e g r a s s o c c u r r e d a f t e r a p p l i c a t i o n o f t r y p t o p h o l a t 6.2 χ 1 0 " M. F u r t h e r m o r e , t r y p t o p h o l was found i n g o o s e g r a s s i n f e c t e d w i t h β. nodulosum. but n o t i n u n i n f e c t e d g r a s s t i s s u e (82)· Phytotoxic a c t i v i t y was found on s e v e r a l o t h e r mono- and d i c o t y l e d o n o u s p l a n t s , but g e n e r a l l y h i g h e r c o n c e n t r a t i o n s were n e c e s s a r y . T r y p t o p h o l and 0 - a c e t y l t r y p t o p h o l have a l s o been i d e n t i f i e d as t r y p t o p h a n m e t a b o l i t e s o f C e r a t o c v s t i s f a a s c e a r u m . a f u n g a l pathogen c a u s i n g oak w i l t (Sfi). 4

Zinniol. Z i n n i o l [13] was f i r s t d e s c r i b e d as a p h y t o t o x i c m e t a b o l i t e o f A l t e r n a r i a z i n n i a e (21). Z i n n i o l i s now known t o be produced by many A l t e r n a r i a s p p . , i n c l u d i n g f u n g a l pathogens o f weeds and c r o p p l a n t s ( Z Î ) . T h i s compound causes n e c r o s i s i n p l a n t s ( Z i ) i 22) and "green i s l a n d " f o r m a t i o n , as d i s c u s s e d e a r l i e r . P h y t o t o x i c Compounds Produced bv Fungal Pathogens o f Crops a n d / o r Non-Pathogenic Fungi A A L - T o x i n . Stem c a n k e r o f tomato 1s caused by t h e f u n g a l pathogen A l t e r n a r i a alternata f. sp. l v c o p e r s i c i (2Î). Concentrations of l e s s t h a t 10 ng/ml o f A A L - t o x i n [ 1 4 ] , a h o s t - s p e c i f i c t o x i n , can produce d i s e a s e symptoms. Two p h y t o t o x i c f r a c t i o n s have been i s o l a t e d from f u n g a l c u l t u r e f i l t r a t e s t h a t reproduce d i s e a s e symptoms i n s u s c e p t i b l e p l a n t s . These f r a c t i o n s a r e termed T and To and each f r a c t i o n has 2 c h e m i c a l components. Collectively t h e s e a r e t h e A A L - t o x i n s . S t r u c t u r a l l y i n T , Ri and Ro OH, Ro - 0oC-CHo-CH(C00H)-CHo-C00H; T o , Ri OoC-CHo-CHtcOOHJ-CHo-COOH, Ro and Ro - OH; T , Ri OH, Ro - 0oC-CHo-CHÎC00H)-CHo-C00H, Ro - H; and Top, A

A 1

A

B 1

Ri

- OoC-CH -CHÎCOOH)-CH2-C06H, 2

R

2

- OH, and Ro « R

(24,

2â). The compound d i s r u p t s p y r i m i d i n e s y n t h e s i s by i n h i b i t i o n o f a s p a r t a t e carbamoyl t r a n s f e r a s e (ACT) (28). Concentrations of A A L - t o x i n o f 10-50 ng/ml cause p o t e n t ACT I n h i b i t i o n . A microtechnique f o r the separation of these s t r u c t u r a l l y r e l a t e d t o x i n s has been a c h i e v e d u s i n g HPLC (22).


1.

HOAGLAND

An Overview

15


Acetylaranotiη. A s o i l f u n g u s , A s p e r g i l l u s t e r r e u s s t r a i n C-520, produces s e v e r a l p l a n t growth r e g u l a t o r s ( 9 8 ) . Three o f t h e s e p h y t o t o x i c compounds have been s t r u c t u r a l l y c h a r a t e r i z e d as acetylaranotiη [ 1 5 ] , b i s - d i t h i o d i ( m e t h y l t h i o ) - a c e t y l a r a n o t i n , and t e r r e i n . Compared t o acetylaranotiη, t h e s e o t h e r compounds were o n l y weakly i n h i b i t o r y i n l e t t u c e and r i c e b i o a s s a y s . A c e t y l aranotiη reduced l e t t u c e r o o t e l o n g a t i o n by 80% a t 10 ppm, and r i c e r o o t l e n g t h by 50% a t 50 ppm and 80% a t 100 ppm. R e s u l t s suggested t h a t t h e d i s u l f i d e b r i d g e 1s r e q u i r e d f o r h i g h e r p h y t o t o x i c i t y . A K - T o x i n . The c a u s a l agent o f b l a c k spot d i s e a s e o f Japanese p e a r , A l t e r n a r i a k i k u c h i a n a . produces two h o s t - s e l e c t i v e t o x i n s : A K - t o x i n [16] I and I I ( 9 2 ) . The t o x i n s Induced n e c r o s i s on s u s c e p t i b l e pear c u l t i v a r l e a v e s a t 65 n g / m l , but no response was noted a t c o n c e n t r a t i o n s up t o 6 . 5 μ%/κΛ i n a r e s i s t a n t c u l t i v a r . A l t e r s o l a n o l A. Pigment a n a l y s i s and t e s t i n g o f compounds from A l t e r n a r i a p o r r i ( E l l i s ) C i f e r r i i n d i c a t e d t h a t t h r e e reduced a n t h r a q u i n o n e s were p h y t o t o x i n s ( 1 0 0 ) . A l t e r s o l a n o l A [17] gave complete i n h i b i t i o n t o r o o t growth a t 100 ppm i n a l e t t u c e b i o a s s a y , and 85% i n h i b i t i o n i n a s t o n e - l e e k b i o a s s a y . T h i s compound was weakly i n h i b i t o r y t o l e t t u c e a t low c o n c e n t r a t i o n s ( 1 2 . 5 and 25 ppm), but t h e s e s o l u t i o n s caused a p p r e c i a b l e i n h i b i t i o n t o s t o n e - l e e k . Analogs a l t e r s o l a n o l Β and d a c t y l a r i o l were l e s s t o x i c t o t h e s e s p e c i e s . Other f u n g a l s p e c i e s such as A. s o l a n i and D a c t v l e r i a l u t e a R o u t i e n a l s o produce t h e s e pigments ( 1 0 0 ) . A M - T o x i n . The pathogen A l t e r n a r i a m a l i causes l e a f spot d i s e a s e o f a p p l e and produces n e c r o t i c s p o t s on f r u i t s , l e a v e s , and s h o o t s o f s u s c e p t i b l e c u l t i v a r s . AM-toxin [ 1 8 ] , a h o s t - s p e c i f i c t o x i n , and s e v e r a l r e l a t e d t o x i n s a r e r e s p o n s i b l e f o r t h e s e symptoms and t h e i r s t r u c t u r e s have been e l u c i d a t e d and c o n f i r m e d by t o t a l synthesis (101-103). A n i s o m v c i n and Methoxvphenone. A n i s o m y c i n [ 1 9 ] , which d i s p l a y s h e r b i c i d a l a c t i v i t y , was f i r s t r e p o r t e d by Yamata e t a l . (104) and was i s o l a t e d from a s o i l Streotomvces s p . B a r n y a r d g r a s s f E c h i n o c l o a c r u s o a l l i ( L . ) Beauv.] and c r a b g r a s s ( D i o i t a r i a s p . ) were s e n s i t i v e , but no h e r b i c i d a l i n j u r y was found on t u r n i p ( B r a s s i c a r a o a L.) o r tomato ( L v c o p e r s i c o n e s c u l e n t u s L . ) . Thus, t h e compound e x h i b i t e d some s e l e c t i v i t y and was t h e f i r s t m i c r o b i a l p r o d u c t used f o r t h e development o f a s y n t h e t i c h e r b i c i d e (methoxyphenone [ 2 0 ] , o r 3,3'-dimethyl-4-methoxy-benzophenone) (105). B i a l a p h o s . P h o s a l a c i n e . and P h o s p h i n o t h r i c i n . These m i c r o b i a l compounds a r e t h e most e n e r g e t i c a l l y r e s e a r c h e d b i o h e r b i c i d e s y e t d i s c o v e r e d . These s t u d i e s encompass e l u c i d a t i o n o f t h e b i o s y n t h e t i c pathways ( b i a l a p h o s and p h o s p h i n o t h r i c i n ) , chemical s y n t h e s i s ( p h o s p h i n o t h r i c i n ) , b a c t e r i a l c l o n i n g and o v e r e x p r e s s i o n o f t h e gene f o r p h o s p h i n o t h r i c i n p r o d u c t i o n , d e t e r m i n a t i o n o f t h e m o l e c u l a r mode o f a c t i o n o f p h o s p h i n o t h r i c i n , and g e n e t i c t r a n s f o r m a t i o n o f t h e p h o s p h i n o t h r i c i n r e s i s t a n c e gene i n t o c r o p p l a n t s . Bialaphos (L-2-amino-4-[(hydroxy)(methyl)phosphinoyl]-butyryl-L-alanyl-L-




OH

Ο

OH

Ο

Alteichin [9]

Stemphyperylenol [10]

Stemphyttoxin [11 ]

CH CH OH 2

2

CH OH

CHj—C=CH CH 0 2

2

2

CH,

CH OH 2

OCHg

Tryptophol [12]

Zinniol [13]

CH : H r — CH 2

™3

0

CH

i l

R

1

CH R

C H x — CH r

( C H J . — CH

*Ί

2

Rg

CH

C H x — CH

OH

OH

ι

*Ί

A A L toxin [14]

Acetylaranotin [15]


CH

0

NH

2

ι

2

HOAGLAND

An Overview

l^J*—CH—CH—C

Ο

C H — C K = C H — C R = C H — C B = C H — COOH

NH—C-CH,


»

3 AK-toxin[16]

CH COO

^OH

a

H,|

HN

>

toxic N H accumulation 4

0 transamidation

Gin

> ^

transamination —>

nucleotide depletion inhibition of protein synthesis toxic accumulation of glyoxylate depletion of Calvin c y c l e intermediates

Figure 4. S i t e s of molecular action of phosphinothricin. (Redrawn f r o m R e f . 116. C o p y r i g h t 1987 V e r l a g de Z e i t s c h r i f t fur Naturforschung).


1. HOAGLAND

An Overview

21


γ-oxygenated p h o s p h i n o t h r i c i n s d i s p l a y e d G S - i n h i b i t o r y p r o p e r t i e s and JJQ v i v o p h y t o t o x l d t y ( 1 2 2 ) . These compounds s h o u l d be u s e f u l t o o l s t o d e t e r m i n e t h e n a t u r e o f m o l e c u l a r b i n d i n g o f phosphinothricin analogs. B i o t e c h n o l o g y and B i o c h e m i s t r y o f B i a l a p h o s P r o d u c t i o n and o f P l a n t s R e s i s t a n t t o B i a l a p h o s . The b l o s y n t h e t 1 c pathway o f b i a l a p h o s p r o d u c t i o n has been e l u c i d a t e d u s i n g C - l a b e l e d p r e s u r s o r s , m e t a b o l i c I n h i b i t o r s , b l o c k e d m u t a n t s , and I d e n t i f i c a t i o n o f p r o d u c t s accumulated and m e t a b o l i z e d by a s e r i e s o f n o n - p r o d u c i n g £. h v d r o s c o p l c u s mutants ( F i g u r e 5) ( 1 2 1 ) . B i a l a p h o s 1s s y n t h e s i z e d from t h r e e carbon p r e c u r s o r s i n a s e r i e s o f a t l e a s t 13 c o n v e r s i o n s . One s t e p i n v o l v e s an a c e t y l - c o e n z y m e Α-dependent r e a c t i o n which m o d i f i e s e i t h e r d e m e t h y l p h o s p h i n o t h r i c i n o r p h o s p h i n o t h r i c i n . T h i s gene which c o n f e r s r e s i s t a n c e t o b i a l a p h o s ( b a r ) has been i s o l a t e d and c h a r a c t e r i z e d from £. h v a r o s c o p i c u s ( 1 2 4 ) . T h i s b a n gene i s both an a n t i b i o t i c - r e s i s t a n t and b i o s y n t h e t i c gene s i n c e i t 1s r e s p o n s i b l e f o r s e l f - d e f e n s e ( r e s i s t a n c e ) o f t h e microbe t o b i a l a p h o s as w e l l as s y n t h e s i s o f t h e h e r b i c i d e ( 1 2 5 ) . The gene encodes a 22kDa1 p o l y p e p t i d e w i t h a c e t y l t r a n s f e r a s e a c t i v i t y ( p h o s p h i n o t h r i c i n a c e t y l t r a n s f e r a s e ) which c a t y l i z e s phosphinothricin to a non-herbicidal acetylated metabolite. R e s e a r c h e r s have i s o l a t e d and c h a r a c t e r i z e d a t r a n s a m i n a s e from £. c o l i K-12, s p e c i f i c f o r p r o d u c t i o n o f L - p h o s p h 1 n o t h r i c i n (126). F u r t h e r work has r e s u l t e d In c l o n i n g , c h a r a c t e r i z a t i o n , and o v e r e x p r e s s i o n o f t h e gene c o d i n g f o r t h e L - p h o s p h i n o t h r i c i n s p e c i f i c t r a n s a m i n a s e from £. c o l i K - 1 2 . These r e s u l t s g r e a t l y f a c i l i t a t e b i o t e c h n o l o g i c a l p r o d u c t i o n o f L - p h o s p h i n o t h r i c i n i n an enzyme r e a c t o r . Host r e c e n t l y , t h e b a r gene has been i n t r o d u c e d and e x p r e s s e d I n t o s e v e r a l p l a n t s p e c i e s u s i n g Aarobacterium-med1ated T1 p l a s m i d t r a n s f o r m a t i o n ( 1 2 7 ) . T r a n s g e n i c p l a n t s (tomato, t o b a c c o , p o t a t o , a l f a l f a , o i l s e e d r a p e , and s u g a r b e e t ) were r e s i s t a n t t o g l u f o s i n a t e and b i a l a p h o s under l a b o r a t o r y and greenhouse c o n d i t i o n s a t f i e l d dose a p p l i c a t i o n s . R e s u l t s o f f i e l d t r i a l s w i l l next a s s e s s e f f e c t s o f more r i g o r o u s e n v i r o n m e n t a l c o n d i t i o n s and q u e s t i o n s o f i n t r o d u c e d - g e n e s t a b i l i t y and p l e i o t r o p h i c e f f e c t s . O t h e r P h y t o t o x i n s Known t o be GS I n h i b i t o r s . L-Methionine s u l f o x i r a i n e (MSO) [25] ( 1 2 8 ) . an a n a l o g o f p h o s p h i n o t h r i c i n , was s y n t h e s i z e d some t i m e ago ( 1 2 9 ) . MSO was a l s o p a t e n t e d as a h e r b i c i d e ( 1 3 0 ) . but p h o s p h i n o t h r i c i n i s c a . 100 t i m e s more i n h i b i t o r y t o GS than 1s MSO ( 1 3 1 ) . 1 3 2 ) . MSO has been r e c e n t l y shown t o o c c u r as a n a t u r a l p r o d u c t , not i n m i c r o b e s , but i n t r e e bark ( C n e s t i s g l a b r a ) ( 1 3 3 ) . However, an a n a l o g o f MSO, L - ( B phosphono) m e t h i o n i n e - S - s u l f o x i m i n e [ 2 6 ] , i s a p o t e n t GS i n h i b i t o r and a m e t a b o l i t e o f L-(M - p h o s p h o n o ) - m e t h i o n i n e - S s u l f o x 1 m i n y l - L - a l a n y l - L - a l a n 1 n e (134) which i s a n o t h e r Streotomvces p r o d u c t ( 1 3 5 ) . Other i m p o r t a n t GS i n h i b i t o r s have been r e p o r t e d . Pseudomonas t a b a c i produces t a b t o x i n i n e - ^ - l a c t a m [ 2 7 ] , a GS i n h i b i t o r ( 1 3 g ) . O x e t i n [ 2 8 ] , d e r i v e d from Streotomvces s p . , i s a r e c e n t l y d i s c o v e r e d GS i n h i b i t o r ( 1 3 7 ) . R e f e r t o F i g u r e 3 .




1 ι

i

I

?

I

1

ο

s

κ» κ»

1.

HOAGLAND

An Overview

23


B o t r v d i e n a l . A new p h y t o t o x i n , b o t r y d i e n a l [29], and two p h y t o t o x i c m e t a b o l i t e s , d e h y d r o b o t r y d i e n a l and d e a c e t y l d i h y d r o bo t r y d i a l , have been I s o l a t e d from a p h y t o p a t h o g e n i c f u n g u s , B o t r v t i s c i n e r e a (13fi). The c o n c e n t r a t i o n o f b o t r y d i e n a l r e q u i r e d t o g i v e a 50% growth I n h i b i t i o n 1n a t u r n i p s e e d l i n g b l o a s s a y was 10 p g / m l . D e h y r o b o t r y d i e n a l and d e a c e t y l d e h y d r o b o t r y d i a l were weaker p h y t o t o x i n s , r e q u i r i n g 10 and 1000 p g / m l , r e p s e c t i v e l y , t o g i v e t h e same I n h i b i t i o n . C e r c o s p o r l n . C e r c o s p o r l n [30] 1s a t o x i n produced by f u n g a l pathogens o f t h e genus C e r c o s p o r a . The compound was f i r s t I s o l a t e d 1n 1957 (132) from t h e soybean pathogen C e r c o s p o r l n k l k u c h i l . Its c h a r a c t e r i z a t i o n and s t r u c t u r e were r e p o r t e d I n d e p e n d e n t l y ( 1 4 0 . 141). The r e d t o x i n causes l i g h t - d e p e n d e n t l i p i d p e r o x i d a t i o n (142) and membrane d i s r u p t i o n i n p l a n t s (1431. by I t s p h o t o s e n s i t i z i n g a c t i o n t h a t produces s i n g l e t oxygen ( 1 4 4 ) . C h a e t o a l o b o s i n s . C y t o c h a l a s i n s Induce s e l e c t i v e r e s p o n s e s i n p l a n t s . C y c l c h a l o s i n Β I s o l a t e d from Phoma e x i o u a was t o x i c t o p e r i w i n k l e f V i n c a minor L.) and t o c h i c o r y ( C i c h o r i u m Intybus L.) (J45) but caused o n l y moderate growth i n h i b i t i o n i n wheat c o l e o p t i l e s ( 1 4 6 ) . C v t o c h a l s l n Η [31] d i d not a f f e c t c o r n p l a n t s , but bean p l a n t s e x h i b i t e d e p a n a s t i c responses and l e a f r o l l i n g ( 1 4 Z ) . In t o b a c c o , t h i s compound d e l a y e d f l o w e r i n g and was a c t i v e a t 10"° M i n wheat c o l e o p t i l e assays (1461. Other e f f e c t s o f c y t o c h a l a s i n s on p l a n t growth have been r e p o r t e d ( 1 4 8 ) . C h a e t o g l o b o s i n Κ was I s o l a t e d from D i p l o d i a macrosoora and shown t o be s t r u c t u r a l l y r e l a t e d t o t h e c y t o c h a l a s i n s [lie). P h y t o t o x i c i t y t e s t s i n d i c a t e d i n h i b i t i o n t o wheat c o l e o p t i l e s a t 1 0 " ' M and may be t h e most a c t i v e c y t o c h a l a s i n tested. C

Citreoviridln. C i t r e o v l r i d l n [32] has been i s o l a t e d from s e v e r a l Pénicillium s p e c i e s ; e . g . £. charTesH (142). The compound e x h i b i t e d s e l e c t i v e and l o n g - t e r m growth I n h i b i t i o n when c o r n (Z£& Mil L . ) , t o b a c c o ( N l c o t i a n a iâbà£Ufl! L . l , and wheat (TrWCUffl a e s t i v u m L.) were t e s t e d a t 10"* t o 10"* M c o n c e n t r a t i o n s . Corn shoot growth was I n h i b i t e d up t o 60 days a f t e r t r e a t m e n t w i t h c i t r e o v i r i d i n a t 10~ M. Wheat c o l e o p t i l e growth was a l s o i n h i b i t e d , but t o b a c c o s e e d l i n g s were not a f f e c t e d a t t h e s e concentrations. z

C l a d o s p o r i n . C l a d o s p o r i n [33] (R-H) has been i s o l a t e d from C l a d o s p o r i u m c l a d o s p o r i o i d e s ( F r e n s e n u i s ) de V r i e s (15Q)» Α$Ρ$Η1ΠΜ? f l a v u s L i n k (1£1), E u r o t l u m s p . [151), and A s p e r g i l l u s reoens (1531. I n i t i a l l y i t was shown t o have a n t i b i o t i c p r o p e r t i e s , but l a t e r c l a d o s p o r i n and c l a d o s p o r i n d i a c e t a t e ( R - C H 3 C O - ) ( s y n t h e t i c a l l y d e r i v e d from c l a d o s p o r i n ) were shown t o have p h y t o t o x i c p r o p e r t i e s . Both compounds were p h y t o t o x i c t o wheat s e e d l i n g s , but had no p h y t o t o x i c e f f e c t s on t o b a c c o s e e d l i n g s . Only c l a d o s p o r i n d i a c e t a t e caused n e c r o s i s , stem c o l l a p s e , and/or growth i n h i b i t i o n i n corn seedlings (153). C o l l e t o t r i c h i n . A pathogenic fungus, C o l l e t o t r i c h u m n i c o t i a n a e . i s t h e c a u s a t i v e agent o f t o b a c c o a n t h r a c n o s e and t h i s organism i s t h e s o u r c e o f t h r e e p h y t o t o x i n s , I n c l u d i n g c o l l e t o t r i c h i n [34] (1M, Hoagland; Microbes and Microbial Products as Herbicides ACS Symposium Series; American Chemical Society: Washington, DC, 1990.



24


1.

HOAGLAND

25

An Overview

1S5). C o l l e t o t r i c h i n ( h a v i n g two h y d r o x y l g r o u p s ) 1s t h e most p h y t o t o x i c o f t h e t h r e e compounds and I n h i b i t e d l e t t u c e h y p o c o t y l and r o o t growth a t c o n c e n t r a t i o n s as low as 3 ppm. C o l l e t o t r i c h i n Β (CHO m o i e t y i n s t e a d o f on r i n g ) i n h i b i t e d r o o t and h y p o c o t y l growth o n l y a t 100 ppm. C o l l e t o t r i c h i n C (CHO m o i e t y i n p l a c e o f OH on s i d e c h a i n ) was l e s s a c t i v e than c o l l e t o t r i c h i n , e x c e p t when c o n c e n t r a t i o n s exceeded 30 ppm, when i t was more i n h i b i t o r y t o r o o t g r o w t h . C o l l e t o t r i c h i n and C o l l e t o t r i c h i n C were a l s o s l i g h t l y more i n h i b i t o r y i n a l e t t u c e g e r m i n a t i o n b l o a s s a y . These l a t t e r compounds a t 1 μ$ a l s o Induced l e s i o n s s i m i l a r t o t h o s e caused by £. n i c o t i a n a e i n p r i c k e d t o b a c c o l e a v e s . C v c l o c a r b a m i d e A and Β. C y c l o c a r b a m l d e A [35] (R - C H - C H ( C H ) ) and Β (R - C H o - f C H g ^ ^ ) were f i r s t i s o l a t e d from S t r e p t o v e r t i c i l l i u m s p . by I s o g a l e t a l . (156) and found t o have p h y t o t o x i c a c t i v i t y , i . e . , complete g e r m i n a t i o n i n h i b i t i o n i n l e t t u c e ( L a c t u c a s a t i v a L.) a t low c o n c e n t r a t i o n (30 ppm). These compounds had no e f f e c t on growth o f emerged s e e d l i n g s , even a t 100 ppm. 2


3

2

Cyclopenin. C y c l o p e n i n [36] and c y c l o p e n o l i s o l a t e d from P é n i c i l l i u m c v c l o p i u m (NRRL 6233) (1£Z) are p h y t o t o x i c compounds c a u s i n g s i g n i f i c a n t growth i n h i b i t i o n i n e t i o l a t e d wheat ( T r i t i c u m a e s t i v i u m ) c o l e o p t i l e s a t 10~ and 10~ M. C y c l o p e n i n was more p o t e n t and caused n e c r o s i s and s t u n t i n g i n c o r n (Zea mavs L.) and m a l f o r m a t i o n s 1n t r i f o l i a t e l e a v e s o f bean ( P h a s e o l u s v u l g a r i s L.) a t 1 0 " M. 3

4

z

D e s m e t h v o x v v i r i d i o l . A new t o x i n from N o d u l i s p o r i u m hinnuleum was i d e n t i f i e d as d e s m e t h o x y v i r i d i o l [37] and shown t o have p h y t o t o x i c p r o p e r t i e s ( 1 5 8 ) . Wheat c o l e o p t i l e s were i n h i b i t e d a t 1 0 " ; t o 1 0 " M and f i r s t I n t e r n o d e s i n o a t s were p l a s m o l v z e d a t 1 0 " M and growth s i g n i f i c a n t l y i n h i b i t e d a t 1 0 " t o 1 0 ' M. Corn t r e a t e d w i t h t h e t o x i n a t 10~ and 10~ M showed n e c r o t i c l e s i o n s and s t u n t i n g a t 10~ M. E f f e c t s on beans and t o b a c c o p l a n t s were e s s e n t i a l l y n i l . V i r l d i o l [38] 1s a s i m i l a r m i c r o b i a l p h o t o t o x i n . A s i m i l a r p h y t o t o x i n i s produced by t h e n o n - p a t h o g e n i c f u n g u s , G l i o c l a d i u m yjrgns (15S). b

3

4

z

7

3

4

Dihydroperaillin. A s p e r g i l l u s u s t u s . a fungus growing on pea (Pisum s a t i v u m ) seeds was found t o produce a p h y t o t o x i c compound, p e r g i l l i n ( 1 6 0 ) . A n o t h e r m e t a b o l i t e from t h i s o r g a n i s m was l a t e r i s o l a t e d and i d e n t i f i e d as d i h y d r o p e r g l l l i n [39] (1611. T h i s s t r u c t u r a l a n a l o g o f p e r g i l l i n was more t o x i c than p e r g i l l i n i n wheat c o l e o p t i l e b i o a s s a y s , i . e . , 1 0 " t o 1 0 " M. 3

4

Fusicoccin. F u s i c o c c i n [40] i s a major m e t a o b l i t e o f t h e fungus Fusicoccum amvodali D e l . , which causes c a n k e r i n almond (Prunus amvodalus B a t s c h ) and peach [£. p e r s i c a ( L . ) B a t s c h ) ] . The compound p l a y s a d e f i n i t e r o l e i n t h e d i s e a s e and i s a d i t e r p e n o i d g l u c o s i d e (162) w i t h h i g h p h y t o t o x i c i t y c a u s i n g w i l t and n e c r o s i s i n many p l a n t s (1631. The c h e m i s t r y and p l a n t growth r e g u l a t i n g p r o p e r t i e s o f f u s i c o c c i n and some d e r i v a t i v e s and a n a l o g s have been summarized and d i s c u s s e d ( 1 6 4 ) .





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27

An Overview


G a b a c u l i n e . T h i s compound 1s a n a t u r a l m e t a b o l i t e f i r s t I s o l a t e d from S t r e o t o m v c e s t o v a c a e n i s and shown t o be a n e u r o t o x i n ( 1 6 5 ) . It 1s a p o w e r f u l I n h i b i t o r o f s e v e r a l p y r l d o x a l p h o s p h a t e - r e q u i r i n g enzymes ( 1 6 6 ) . G a b a c u l l n e [41] was o r i g i n a l l y r e p o r t e d as an I n h i b i t o r o f gamma-aminobutyrate a m i n o t r a n s f e r a s e and s t r o n g l y I n h i b i t s c h l o r o p h y l l s y n t h e s i s 1n p l a n t s ( l f i Z , l f i f i ) . It Inhibits t e t r a p y r r o l e s y n t h e s i s (169) by b l o c k i n g 5-am1nolevul1nate f o r m a t i o n i n p l a n t s v i a I n h i b i t i o n o f 5-aminolevulinate dehydratase (170). G e l d a n a m v c i n . Geldanamycin [42] was f i r s t r e p o r t e d as a p r o d u c t o f StrePtQiwÇgS h v o r o s c o p l c u s v a r . a e l d a n u s (121, 122). This compound (an ansamycin a n t i b i o t i c , 1s v e r y s i m i l a r t o h e r b i m y c i n B, d i f f e r i n g o n l y i n t h e p r e s e n c e o f a methoxyl group a t carbon number 17 (122). H e r b i m y c i n s , a l s o ansamycin a n t i b i o t i c s produced by a s t r a i n o f S- h y g r o s c o o i c u s . a r e h e r b i c i d a l and a c t i v e a g a i n s t v a r i o u s d i c o t y l e d o n o u s and monocotyledonous p l a n t s ( 1 7 3 - 1 7 5 ) . Geldanamycin caused a 50% r e d u c t i o n i n garden c r e s s ( L e o i d l u m s a t i v u m L.) r a d i c l e growth a t 1-2 ppm and n e a r l y 100% i n h i b i t i o n a t 3-4 ppm. A t h i g h c o n c e n t r a t i o n s , geldanamycin caused s e v e r e n e c r o s i s and d i s i n t e g r a t i o n o f r a d i c l e s . Gostatln. G o s t a t i n [43] I n h i b i t s a s p a r t a t e a m i n o t r a n s f e r a s e i n wheat germ ( 1 7 6 ) . There i s a s i m i l a r i t y i n t h e mode o f a c t i o n o f g o s t a t i n and g a b a c u l l n e [41] ( 1 7 7 ) . HC-Toxin. E a r l y a t t e m p t s t o I s o l a t e and c h a r a c t e r i z e t h i s t o x i n from a c o r n pathogen, H e l m i n t h o s p o r l u m c a r b o n s r a c e 1 were performed i n 1967-71 (123, 1 7 9 ) . Many o t h e r r e p o r t s o f s t r u c t u r e d e t e r m i n a t i o n s have been summarized ( 1 8 0 ) . P u r i f i e d HC-toxin [ 4 4 ] , a h o s t - s p e c i f i c t o x i n , causes s u b s t a n t i a l r o o t growth i n h i b i t i o n a t c a 0 . 5 pg/ml ( 1 8 1 ) . A v e r y s i m i l a r compound, c h l a m y d o c i n [ 4 5 ] , has been I s o l a t e d from D i h e t e r o s o o r a çhUfnydQSPQni (182, 131). Herbiddins. Herb1cid1ns A [46] (Ri and Ro - CHo, Ro C0(CH 0H)C-CHCH ) and Β ( R j and R - C H , R - HJ have been produced by Streotomvces s a a a n o n e n s i s and have been examined f o r h e r b i c i d a l a c t i v i t y i n many mono- and d i c o t y l e d e n o u s p l a n t s . O t h e r a n a l o g s , h e r b i d d i n s E, F, and G, have a l s o been i d e n t i f i e d , but n o t examined f o r h e r b i c i d a l a c t i v i t y ( 1 8 4 - 1 8 8 ) . 2

3

3

3

2

I r o e x i l and Benzadox. A wood-degrading basidlorçycete, I r o e x oachvodon. produces i r p e x i l [47], which had a n t i b a c t e r i a l a c t i v i t y (189). L a t e r , t h e compound was found t o have p h y t o t o x i c p r o p e r t i e s and t o be s t r u c t u r a l l y r e l a t e d t o s e v e r a l s y n t h e t i c h e r b i c i d e s , i n c l u d i n g benzadox ( b e n z a m i d o - o x y a c e t i c a c i d ) [48] (28)· Benzadox (and p r e s u m a b l y , i r p e x i l ) a c t s v i a m e t a b o l i c c o n v e r s i o n w i t h i n p l a n t s t o form ami no-oxy a c e t i c a d d , w h i c h 1s a p o t e n t p y r l d o x y l p h o s p h a t e - r e q u i r i n g enzyme i n h i b i t o r (190) and a l s o a non-commercial s y n t h e t i c h e r b i c i d e ( 1 9 1 . 1 9 2 ) . Macro!ides. R e c i f e l o l i d e [ 4 9 ] , a f u n g a l p r o d u c t from C e o h a l o s p o r i u m r e c i f e l A r e a Leao e t Lobo was a weak growth I n h i b i t o r when t e s t e d a t 100 ppm on g e r m i n a t i n g l e t t u c e ( 1 9 3 ) . Other m a c r o l i d e s such as c l a d o s p o l i d e A & Β from C l a d o s o o r i u m



MICROBES A N D MICROBIAL PRODUCTS AS HERBICIDES

Benzadox [48]

Rectfeiolide [49]


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An Overview

c l a d o s p o r i o i d e s (193) were a c t i v e a t 100 ppm; I . e . , c l a d o s p o l i d e A I n h i b i t e d r o o t growth ca 60X, but c l a d o s p o l i d e Β showed growth promotion p o t e n t i a l . C1s- and t r a n s - r e s o r c y U d e a t 100 ppm I n h i b i t e d growth o f l e t t u c e , r i c e f O r v z a s a t l v a L . ) , and C h i n e s e cabbage ( B r a s s i c a p e k l n e n s i s ) r o o t s . L i g h t c a t a l y z e d 1 n t e r c o n v e r s 1 o n o f £ i s and t r a n s Isomers i n methanolc s o l u t i o n s ( 1 9 4 ) . D e h y d r o c u r v u l a r i n [50] from A l t e r n a r i a a l t e r n a t a ( F r i e s ) K e i s s l e r and v a r i o u s s y n t h e t i c a l l y d e r i v e d a n a l o g s showed v a r y i n g degrees o f growth I n h i b i t i o n i n an e t i o l a t e d wheat c o l e o p t i l e t e s t


US5).

M e v i n o l i n . M e v i n o l i n [51] i s a m e t a b o l i t e o f t h e ascomycete Aspergillus terreus. It i s a highly s p e c i f i c i n h i b i t o r of 3 - h y d r o x y - 3 - m e t h y l g l u t a r y l coenzyme A r e d u c t a s e i n a wide v a r i e t y o f e u k a r y o t e s and p r o k a r y o t e s (18Ê-1S2). The compound causes r o o t growth I n h i b i t i o n i n l i g h t - o r dark-grown s e e d i n g s a t c o n c e n t r a t i o n s as low as ca 1 0 ' t o 1 0 " M (1991. I t a l s o lowers phytosterol p r o d u c t i o n (2001. 7

8

M o n i l i f o r m i n . The f u n g i Fusarium m o n i l i f o r m e and £. f u s a r i o d e s . pathogens o f c o r n and m i l l e t , r e s p e c t i v e l y , produce t h e p h y t o t o x i n moniliformin (3-hydroxycyclobut-3-ene-l,2-dione) [52]. This compound i n d u c e s c h l o r o s i s and n e c r o s i s i n c o r n , wheat and b a r l e y and i n h i b i t s growth i n tomato, soybeans, and t o b a c c o ( 2 0 1 . 2 0 2 ) . Because o f the p h y t o t o x i c a c t i v i t y o f m o n i l i f o r m i n and t h e r e l a t i v e l y s i m p l e s t r u c t u r e , numerous s y n t h e s e s o f t h i s compound and a n a l o g s have been c a r r i e d out t o o b t a i n h e r b i c i d a l compounds as d i s c u s s e d by F i s c h e r and B e l l u s {13). A l t h o u g h some compounds were v e r y e f f e c t i v e h e r b i c i d e s , no c r o p s e l e c t i v i t y was o b t a i n e d . F u r t h e r m o r e , m o n i l i f o r m i n was found t o be t o x i c t o v e r t e b r a t e s and mammals ( 2 0 1 - 2 0 3 ) . N i g e r a z i n e A and B. N i g e r a z i n e Β ( M - m e t h y l - t r a n s - 2 , 5 - d i m e t h y l - N ' cinnamoyl p i p e r a z l n e ) [53] (Rj - H, R - C H ) was r e p o r t e d (204) from A s p e r g i l l u s n i a e r about two y e a r s p r i o r t o i d e n t i f i c a t i o n o f N i g e r a z i n e A (Rj - C H , R - H) ( 2 0 5 ) . In t e s t s w i t h l e t t u c e s e e d l i n g s , both compounds showed s i g n i f i c a n t r o o t growth i n h i b i t i o n (ca 40-80% a t 100-400 ppm). 2

3

3

2

Nigericin. N i g e r i c i n [54] was f i r s t r e p o r t e d i n 1949 (206) and l a t e r found i d e n t i c a l t o p o l y e t h e r i n A, a m e t a b o l i t e o f Streotomvces h y g r o s c o p i c u s ( 2 0 7 ) . The compound i s an lonophore and a f f e c t s p o t a s s i u m i o n t r a n s p o r t i n m i t o c h o n d r i a l , c h l o r o p l a s t , and microsomal membranes (208-212) and i n h i b i t s p h o t o p h o s p h o r y l a t i o n (208). I t a l s o has p h y t o t o x i c p r o p e r t i e s as demonstrated i n an i n t a c t garden c r e s s s e e d l i n g b l o a s s a y (211). A l t h o u g h n i g e r i c i n caused a 50% r e d u c t i o n i n garden c r e s s r a d i c l e growth a t 1-2 ppm, no v i s i b l e n e c r o s i s was e v i d e n t . O o s p o r e i n . A s t r a i n o f Chaetomium t r i l a t é r a l e was found t o produce a r e d c r y s t a l l i n e m e t a b o l i t e w i t h g r o w t h - i n h i b i t i n g and p h y t o t o x i c p r o p e r t i e s when t e s t e d on o a t , t o b a c c o , and bean ( 2 1 4 ) . This compound [55] i s a l s o produced by s e v e r a l o t h e r f u n g i and f u n g i i m p e r f e c t i ( 2 1 5 . 216) ascomycetes (217) and b a s i d i o m y c e t e s (21fi). T h i s compound was a l s o t o x i c t o v e r t e b r a t e s ( 2 1 4 ) . Hoagland; Microbes and Microbial Products as Herbicides ACS Symposium Series; American Chemical Society: Washington, DC, 1990.



Moniliformin [52]

Nigerazine [53]

Odandin[56]


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An Overview

O r ! a n d i n . A new m e t a b o l i t e , named o r l a n d i n [56], was I s o l a t e d from A s p e r g i l l u s n l o e r on c i t r u s l e a v e s and c h e m i c a l l y c h a r a c t e r i z e d as b 1 s [ 8 , 8 ' - ( 7 - h y d r o x y - 4 - m e t h g x y - 5 - m e t h y l c o u r m a r 1 n ] . The compound was p h y t o t o x i c a t 10" t o 10" M i n a wheat c o l e o p t i l e growth a s s a y ( 2 1 9 ) . K o t a n i n , a v e r y s i m i l a r compound, was I s o l a t e d from fi. qUuÇtiS (22fl) and l a t e r I d e n t i f i e d as fi. c l a v a t u s {221). However, k o t a n i n was not p h y t o t o x i c t o wheat (212) and methyl a t i o n o f t h e 2 hydroxy groups o f o r l a n d i n caused l o s s o f p h y t o t o x i c i t y .


3

b

P r e h e l m i n t h o s p o r a l . S e v e r a l p l a n t growth r e g u l a t o r compounds have been I s o l a t e d and I d e n t i f i e d from Helm1nthospor1um s a t i v u m r D r e s c h l e r a s o r o k i a n a l . H e l m i n t h o s p o r a l was found t o be a growth promoter i n r i c e s e e d l i n g s , but I n h i b i t o r y t o wheat ( 2 2 2 . 2 2 2 ) . S y n t h e t i c a n a l o g s had d i f f e r e n t i a l e f f e c t s on l e t t u c e and r i c e growth ( 2 2 4 ) . P r e h e l m i n t h o s p o r a l [57] from β. s o r o k i a n a was I s o l a t e d and t h e a c e t a t e d e r i v a t i v e s y n t h e s i z e d ( 2 2 5 ) . Both compounds i n h i b i t e d wheat c o l e o o t l l e growth a t l O ^ a n d Ι Ο " M and both promoted growth a t 10" M. Both compounds caused s t u n t i n g and c h l o r o s i s i n c o r n and no réponse i n t o b a c c o p l a n t s , but o n l y t h e a c e t a t e d e r i v a t i v e caused n e c r o s i s i n bean. 4

b

R a d i c i n i n . D e o x v r a d 1 c i n 1 n . 3 - E p i d e o x v r a d 1 c 1 n o 1 . and R a d i a n t h i n . A l t e r n a r i a h e l i a n t h i . a major pathogen o f s u n f l o w e r ( H e l i a n t h u s a n n u u s ) . produces s e v e r a l p h y t o t o x i n s . R a d i c i n i n [ 5 8 ] , d e o x y r a d i c i n i n , and 3 - e p 1 d e o x y r a d i c i n o l [59] were r e p o r t e d e a r l y (226. 2 2 7 ) . F u r t h e r work has I s o l a t e d d e o x y r a d i c i n o l and r a d i a n t h i n [60] ( 2 2 8 ) . S t u d i e s on r a d i c i n i n b i o s y n t h e s i s have i n d i c a t e d t h e compound i s d e r i v e d from p o l y k e t i d e s (229. 2 3 0 ) . D e o x y r a d i c i n i n i s a l s o o f p o l y k e t i d e o r i g i n ( 2 2 7 ) . R e c e n t l y t h e mechanism o f polyketlde-derived biosynthesis of deoxyradicinin, deoxyradicinol, and 3 - e p i d e o x y r a d i c i n o l has been shown t o o c c u r v i a c o n d e n s a t i o n o f two p o l y k e t i d e c h a i n s r a t h e r than from c y c l y a t i o n and r i n g - c l e a v a g e of a s i n g l e hexaketide u n i t (231). T g n t P X i n - A l t e r n a r i a a l t e r n a t a produces t e n t o x i n [61], a cyclic t e t r a p e p t i d e . T h i s p h y t o t o x i n causes I n j u r y t o many monocotyledonous and d i c o t y l e d o n o u s weed s p e c i e s , but does not i n j u r e maize (Zea mavs L.) o r soybean ( G l y c i n e max L. M e r r . ) ( 2 2 ) . T e n t o x i n has been s y n t h e s i z e d i n t h e l a b ( 2 3 2 ) . S i t e s o f a c t i o n o f t h i s t o x i n a r e d i s r u p t i o n o f energy t r a n s f e r by I n h i b i t i o n o f CFi ATPase (233) and a l t e r a t i o n o f n u c l e a r - c o d e d p r o t e i n uptake ( 2 2 4 ) . Tenuazonic A c i d . Tenuazonic a d d [62] 1s a f u n g a l m e t a b o l i t e t h a t has a broad p h y t o t o x i c i t y spectrum (soybean, r i c e , D a t u r a i n n o x i a . and l e t t u c e ) ( 2 3 5 - 2 3 7 ) . T o x i c i t y t o p l a n t s has been a t t r i b u t e d t o reduced p r o t e i n s y n t h e s i s v i a ribosome i n h i b i t i o n (22a, 2 2 8 ) . T e r o h e n v l l i n and H y d r o x y t e r p h e n v l l i n . H y d r o x y t e r p h e n y l l l n [63] and t e r p h e n y l l i n a r e produced by A s p e r g i l l u s c a n d i d u s ( 2 2 S ) Terphenyllin (2',5'-dimethyoxy-4,3',4"-tr1hydroxy-fi-terphenyl) i n h i b i t e d wheat c o l e o p t i l e growth a t - 1 0 " M w h i l e t h e h y d r o x y a n a l o g was i n h i b i t o r y a t 1 0 ' t o 1 0 ' M. The t e t r a a c e t a t e o f h y r d r o x y t e r p h e n y l l i n was not p h y t o t o x i c t o wheat c o l e o p t i l e s . 3

3

5



32


Tenuazonic acid [62]

Tentoxin [61]

H C H

2

= CH

C = i

OCHg

OH

Hydroxyterphenyilin [63]

H

C— H C T ^ C H ,

3 Thiolactomycin [64]


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An Overview

T h i o l a c t o m v c i n . T h i o l a c t o m y c i n [64] from N o r c a r d l a s p . No. 2-200 i s a s p e c i f i c i n h i b i t o r o f t y p e I I f a t t y a c i d s y n t h e t a s e i n h i g h e r p l a n t s and £. c o l i ( 2 4 0 ) . The acetyl-CoA:ACΡ S - a c e t y l - t r a n s f e r a s e i s t h e apparent s p e c i f i c s i t e o f i n h i b i t i o n (Ml). A n o t h e r a n t i b i o t i c , c e r u l e n i n ( s t r u c t u r e not shown) i n h b i t s 0 - k e t o c o c y l - A C P s y n t h e t a s e I i n b a c t e r i a , f u n g i , and p l a n t s , but a l s o i s i n h i b i t o r y t o o t h e r s i t e s such as p o l y k e t i d e and s t e r o l b i o s y n t h e s i s ( 2 4 2 - 2 4 4 ) . C e r u l e n i n and t h i o l a c t o m y c i n i n h i b i t e d CQ14W-acetate i n c o r p o r a t i o n i n t o f a t t y a c i d s a t I Q v a l u e s o f 50 and 4 uM, r e s p e c t i v e l y ( 2 4 5 ) . R e c e n t l y c y c l o h e x a n e d i o n e h e r b i c i d e s have been shown t o i n h i b i t l i p i d b i o s y n t h e s i s by i n h i b i t i o n o f acetyl-CoA carboxylase (246).


5

Tovocamvcin. Streotomvces t o v a c a e n s i s produces a p h y t o t o x i n , t o y a c a m y c i n [65] ( 2 4 7 ) . A Streotomvces s p . a l s o produced t o y a c a m y c i n which was i n h i b i t o r y t o growth o f r i c e , b a r n y a r d g r a s s , c r a b g r a s s ( D i o i t a r i a s a n a u i r a l i s ) . l u c e r n e , t u r n i p , and tomato (1M). Other s t r u c t u r a l l y r e l a t e d p h y t o t o x i c analogs are s a n g i v a m y c i n [ 6 6 ] , t u b e r c i d i n [ 6 7 ] , and h e r b i p l a n i n [68] (MS). Trichothecenes. Macrocvclic Trichothecens. These t r i c h o t h e c e n s p o s s e s s a wide range o f p h y t o t o x i c s p e c i f i c i t y . Y e r r u c a r i n A, J , and t r i c h o v e r r i n Β are i n h i b i t o r y i n t h e e t i o l a t e d wheat c o l e o p t i l e t e s t a t v e r y low c o n c e n t r a t i o n s ( 1 0 " M) ( 2 4 9 ) . R o r l d i n A [69] was v e r y t o x i c t o t o b a c c o , c o r n , and bean ( P h a s e o l u s v u l a a r e L.) s e e d l i n g s ( 2 4 9 ) . T r i c h o t h e c e n e s a l s o a r e found i n t h e s o i l m i c r o o r g a n i s m s Mvothecium v e r r u c a r i a ( A l b e r t i n i e t S c h w e i n i t z ) D i t m a r ex F r i e s and M. r o r i d u m Tode ex F r i e s ( 2 5 0 ) . A B r a z i l i a n s h r u b , B a c c h a r i s meaapotamica. c o n t a i n s h i g h l e v e l s o f t r i c h o t h e c e n s ( b a c c h a r i n o i d s ) which a r e c l o s e l y r e l a t e d t o t h e m a c r o c y c l i c t r i c h o t h e c e n s such as r o r i d i n A and t h e v e r r u c a r i n s (2§0). These compounds a r e a b s o r b e d , m e t a b o l i z e d , t r a n s l o c a t e d , and accumulated i n t h e shrubs a f t e r b e i n g produced by s o i l m i c r o o r g a n i s m s . The b a c c h e r i n o i d s a r e h i g h l y p h o t o t o x i c e x c e p t t o 8. megapotarnica and may be i m p o r t a n t adopted a l l e l o c h e m i c a l s i n p l a n t ecosystems c o m p l e t i n g w i t h t h e s e shrubs ( 2 5 1 ) . Simple Trichothecens. F u s a r i urn t r i c i n c t u m . i s o l a t e d from peanuts r e m a i n i n g i n s o i l a f t e r h a r v e s t , produced a t r i c h o t h e c e n e compound, n e o s o l i n i o l monoacetate [ 7 0 ] , which was a v e r y p o t e n t growth i n h i b i t o r i n wheat c o l e o p t i l e b i o a s s a y s a t c o n c e n t r a t i o n s as low a t 1 0 " M. In c o n t r a s t , the compound d i d not cause complete growth i n h i b i t i o n at 1 0 " M. A s i m i l a r compound, d i a c e t o x y s c i r p e n o l , caused s l i g h t growth i n h i b i t i o n i n pea s e e d l i n g s a t 2.7 χ 1 0 " M and s e v e r e i n h i b i t i o n a t 2.7 χ 1 0 " M, but was not t o x i c t o wheat s e e d l i n g s ( 2 5 2 ) . 7

b

3

b

5

Triticones. P h y t o t o x i c t r i t i c o n e s have been found i n D r e c h s l e r a t r i t i c i - r e o e n t i s . a p l a n t pathogen t h a t causes t a n spot on wheat, and i n C u r v u l a r i a c l e v a t a . a pathogen o f s e v e r a l g r a s s e s ( 2 5 3 ) . At l e a s t e i g h t t r i t i c o n e s have been i d e n t i f i e d , but o n l y t r i t i c o n e s A [71] and Β are p h y t o t o x i c . These compounds p o s s e s s an e x o c y c l i c d o u b l e bond a d j a c e n t t o a ketone m o i e t y .



CH OCCH 2

3


Neosolaniol monoacetate [70]

C — Nil | ^ H CH —CH 3

CHx— C H

3

COOH

2

Coronatine [72] TriticoneA[71]

o—CH

3

Cyanobacterin [73]

2

N—S0 —Ο—Ρ—NH—(CH^—CH—C—ala—homoarg 2

OH

NH

0

Phaseolotoxin [74]

C H x — CH

I

OH

I

NH

CHx— Ο

C H = CH

CH

COOH

I

NH„

0

Rhizobitoxine [75]


1. HOAGLAND

An Overview

35

B a c t e r i a l P h v t o x i n s from Crop Pathogens and Weed Pathogens


C o r o n a t i n e . C o r o n a t i n e [ 7 2 ] was f i r s t d e t e c t e d i n I s o l a t e s o f l i q u i d c u l t u r e s o f Pseudomonas s v r i n o a e p v . a t r o o u r p u r e a . a pathogen o f r y e g r a s s ( 2 5 4 ) . T h i s p a t h o v a r a l s o produces a n o t h e r p h y t o t o x i c s t r u c t u r a l a n a l o g o f c o r o n a t i n e , M - c o r o n a f a c o y l v a l i n e (2551. C o r o n a t i n e a p p l i e d t o I t a l i a n r y e g r a s s l e a v e s caused c h l o r s i s and browning ( 2 5 4 ) . i t was a l s o p h y t o t o x i c t o soybean ( 2 5 6 ) . Coronatine i s produced by s e v e r a l £. s v r i n o a e pathogens such as pv o l v c i n e a (25Z), p v . tPfMtQ (258. 252), p v . morsorunorum (26fl), pathogens o f soybean, tomato, and Prunus s p p . , r e s p e c t i v e l y . R e c e n t l y a p l a s m i d (pPT23A) was shown t o mediate p r o d u c t i o n o f c o r o n a t i n e i n £. s v r i n o a e p v . tomato (261). C v a n o b a c t e r i n . A d l a r y l - s u b s t i t u t e d γ-lactone, c y a n o b a c t e r l n [ 7 3 ] , was I s o l a t e d from t h e c y a n o b a c t e r i u m , Scvtonemoa h o f m a n n l . a b l u e - g r e e n a l g a e , and 1s a p o t e n t i n h i b i t o r o f p h o t o s y n t h e s i s i n h i g h e r p l a n t s (Lemna q i b b a . c o r n , peas) and a l g a e (252)· The c o n c e n t r a t i o n r e q u i r e d t o I n h i b i t t h e H i l l r e a c t i o n i n PS I I was g e n e r a l l y l o w e r than t h a t f o r t h e c l a s s i c h e r b i c i d a l H i l l I n h i b i t o r d i u r o n (DCMU; N ' - ( 3 , 4 - d 1 c h l o r o p h e n y l ) - Μ,Μ-dimethylurea). The compound d i d n o t a f f e c t e l e c t r o n t r a n s p o r t i n PS I . The b i n d i n g s i t e o f I n h i b i t i o n may be t h e D - l q u i n o n e - b i n d i n g p r o t e i n (281)· A l t e r i n g s u b s t i t u e n t s o f t h e phenyl r i n g i n t h i s m o l e c u l e produced l e s s p h y t o t o x i c analogs (264). P h a s e o l o t o x i n . Pseudomonas s v r i n o a e p v . p h a s e o l i c o l a 1s t h e o n l y b a c t e r i a l s p e c i e s known t o produce p h a s e o l o t o x i n [ 7 4 ] . However, t h e pathogen has many h o s t s : bean, pigeon p e a , G l y c i n e w i o h t i i . FfàçrQPtmiMffl atroourpurem ( s l r a t o ) . DoUçhPS s p p . , (yam bean) P a c h v r r h i z u s o r o s u s . and (mungbean) V1ona r a d i a t a (285), which demonstrates a broad p h y t o t o x i c i t y r a n g e . T h i s t o x i n i s t r a n s l o c a t e d w i t h i n t h e p l a n t and moves t o a p i c a l m e r i s t e m a t i c t i s s u e where i t r e t a r d s growth and a l t e r s a p i c a l dominance (268» 2 6 7 ) . The s i t e o f a c t i o n o f t h i s compound i s o r n i t h i n e carbamoyl t r a n s f e r a s e , which r e g u l a t e s a r g i n i n e s y n t h e s i s (268)· R h i z o b i t o x i n e . V a r i o u s Rhizoblum .1 anon 1 cum s t r a i n s produce r h i z o b i t o x i n e [ 7 5 ] , whose s t r u c t u r e was r e p o r t e d i n 1972 (282)· A l t h o u g h t h e h o s t o f t h i s b a c t e r i u m i s soybean, t h i s compound i s a l s o p h y t o t o x i c t o many o t h e r p l a n t s p e c i e s . T h i s p h y t o t o x i n i s an a n a l o g o f c y s t a t h i o n i n e and a c t s as an i r r e v e r s i b l e i n h i b i t o r o f 0 - c y s t a t h i o n a s e which c a t a l y z e s p r o d u c t i o n o f homoserine from cystathionine (270). Rhizobitoxine also I n h i b i t s ethylene p r o d u c t i o n from m e t h i o n i n e ( 2 7 1 ) . as does a s i m i l a r p h y t o t o x i n , 2-amino-4-methoxy-3-eno1c a c i d (28)· S t i o m a t e l l i n . A myxobacteriales species, Stiomatella auront!aca. produces an a n t i b i o t i c s t i g m a t e l l i n [76] which a l s o has h e r b i c i d a l p r o p e r t i e s ( 2 7 2 ) . T h i s dlmethoxychromone a l t e r s photosynthetic electron transport at the herbicide-binding protein and t h e cytochrome b g / f complex. T a b t o x i n . The p h y t o t o x i c compound t a b t o x i n [77] 1s e x c r e t e d by Pseudomonas s v r i n g a e s p . iafeailL, as w e l l as o t h e r s t r a i n s , and i s




36


1.

HOAGLAND

37

An Overview


t h e c a u s a l agent o f c h l o r o s i s and n e c r o s i s a s s o c i a t e d w i t h w i l d f i r e d i s e a s e ( 2 7 3 ) . T h i s p h y t o t o x i n has been known f o r some t i m e t o I n h i b i t GS a c t i v i t y (2741 which was s u p p o r t e d by t h e f a c t t h a t supplemental g l u t a m i n e r e v e r s e d i n d u c t i o n o f l e a f c h l o r o s i s . Later s t u d i e s , however, i n d i c a t e d t h a t h y d r o l y s i s o f t a b t o x i n t o t a b t o x i n i m e - 0 - 1 actam o c c u r r e d and t h a t t h e l a t t e r compound a c t e d as t h e GS i n h i b i t o r ( 2 7 5 ) . T a a e t i t o x i n . The b a c t e r i a l p h y t o t o x i n t a g e t i t o x i n [78] i s produced by Pseudomonas s v r i n o a e p v . t a a e t i s . I t causes c h l o r o s i s i n m a r i g o l d ( T a o e t i s o a t u l c L.) and z i n n i a ( H e l i o o s i s s p . ) a t ng l e v e l s and has been I s o l a t e d , p u r i f i e d ( 2 7 6 ) . and s t r u c t u r a l l y c h a r a c t e r i z e d ( 2 7 7 ) . C h l o r o s i s o c c u r s i n d e v e l o p i n g but not mature l e a v e s (27fi, 2 7 8 ) . U l t r a s t r u c t u r a l and p h y s i o l o g i c a l e v i d e n c e i n d i c a t e s t h a t t h e p h y t o t o x i c e f f e c t s may be r e l a t i v e l y p l a s t i d s p e c i f i c (279. 2 8 0 ) . Wheat s e e d l i n g s t r e a t e d w i t h t h e t o x i n produce p i g m e n t - d e f i c i e n t l e a v e s , l a c k i n g both l a r g e and s m a l l s u b u n i t s o f r i b o s e 1 , 5 , - d i s p h o s p h a t e c a r b o x y l a s e (RuBPCase), and t h e i r r e s p e c t i v e p i a s t i d - e n c o d e d and n u c l e a r encoded mRNA's ( 2 8 1 ) . F u r t h e r m o r e , p l a s m i d (70S) ribosomes and c y t o s o l i c (80S) ribosomes a r e d e p l e t e d by t o x i n a c t i o n . T a g e t i t o x i n I n h i b i t s RNA polymerase i n c h l o r o p l a s t e x t r a c t s from pea; however, wheat germ RNA polymerase II i s I n s e n s i t i v e to the phytotoxin (282). Tagetetoxin a l s o i n h i b i t s e u k a r y o t i c RNA polymerase I I I ( 2 8 3 ) . Many o t h e r p h y t o t o x i n s not p r e s e n t e d here have been s t r u c t u r a l l y c h a r a c t e r i z e d and t e s t e d i n some p l a n t b i o a s s a y s y s t e m s . Numerous o t h e r reported p h y t o t o x i n s t u d i e s are i n the " a c t i v e f r a c t i o n " stage and s t r u c t u r e e l u c i d a t i o n o f t h e a c t i v e components has not been a c h i e v e d . N e v e r t h e l e s s , from t h e d a t a p r e s e n t e d , i t can g e n e r a l l y be c o n c l u d e d t h a t : d i v e r s e m i c r o b e s produce a broad range o f c h e m i s t r i e s w i t h p h y t o t o x i c a c t i v i t i e s ; c h e m i c a l and b i o c h e m i c a l s y n t h e s i s o f almost a l l o f t h e s e compounds i s unknown (but d e r i v i t i z a t i o n s t u d i e s t o a l t e r p h y t o t o x i c a c t i v i t y have been used i n a few i n s t a n c e s ) ; knowledge o f t h e spectrum o f s p e c i e s s u s c e p t i b l e t o t h e s e compounds i s i n c o m p l e t e (many weed and c r o p s p e c i e s have not been t e s t e d ; some compounds a r e t o x i c t o organisms o t h e r t h a n p l a n t s ) ; and t h e m o l e c u l a r mode o f p h y t o t o x i n a c t i o n i s u n s t u d i e d o r unknown f o r most. The major e x c e p t i o n 1s t h e v a s t amount o f d a t a on b i a l a p h o s , p h o s a l a c i n e , and p h o s p h i n o t h r i c i n , which have a c h i e v e d commercial s t a t u s . H e r b i c i d e . B i o h e r b i c l d e . and M i c r o b i a l

Phytotoxin Targets

From t h e s u r v e y o f m i c r o b i a l compounds w i t h p h y t o t o x i c i t y , i t can be noted t h a t mode o f a c t i o n s t u d i e s a r e g e n e r a l l y l a c k i n g . However, mode o f a c t i o n and m o l e c u l a r t a r g e t s i t e i n v e s t i g a t i o n s g e n e r a l l y o c c u r o n l y a f t e r a p a r t i c u l a r compounds has reached market s t a t u s . As p o i n t e d out p r e v i o u s l y , most h e r b i c i d e s have been d i s c o v e r e d u s i n g random s c r e e n i n g programs r a t h e r than from an a p p l i e d r a t i o n a l approach t o h e r b i c i d e d e s i g n , t a r g e t , and s y n t h e s i s . A few attempts t o r a t i o n a l l y d e s i g n h e r b i c i d e s chose i n h i b i t i o n o f s i t e s o f p h o t o p h o s p h o r y l a t i o n u n c o u p l e r s ( 2 8 4 ) . g l y c o l a t e o x i d a s e (2S5), o x i d a t i o n o f i n d o l e a c e t i c a d d (IAA) by p e r o x i d a s e ( 2 8 6 ) . and secondary p l a n t m e t a b o l i s m , i . e . , p h e n l y a l a n i n e ammonia-lyase (£27)



38

MICROBES A N D MICROBIAL PRODUCTS AS HERBICIDES

and s h i k i m a t e dehydrogenase ( 2 8 8 ) . Some I n h i b i t o r s d e s i g n e d f o r t h e s e s i t e s were e f f e c t i v e but none o f t h e compounds reached commercial h e r b i c i d e development. I t i s very probable that other u n p u b l i s h e d r a t i o n a l approaches t o h e r b i c i d e development have ended i n a s i m i l a r manner. A v a r i e t y o f somewhat g e n e r a l t a r g e t s f o r h e r b i c i d a l a c t i o n have been known f o r some t i m e (282) and knowledge o f h e r b i c i d e ( o r i n h i b i t o r ) a c t i o n I m p l i c a t e s some o f t h e s e g e n e r a l and s p e c i f i c s i t e s t o be a l t e r e d by c e r t a i n compounds (290-293) ( F i g u r e 6). Changes 1n t h e b i o c h e m i s t r y a t some o f t h e s e s i t e s , when a f f e c t e d by adequate h e r b i c i d e ( o r I n h i b i t o r ) c o n c e n t r a t i o n , can l e a d t o p l a n t d e a t h . N a t u r a l e v o l u t i o n a r y p r o c e s s e s i n p l a n t pathogens have r e s u l t e d i n a ' r a t i o n a l ' o r s e l e c t i v e d e s i g n o f p h y t o t o x i n s f o r c e r t a i n p l a n t s and m o l e c u l a r s i t e s w i t h i n p l a n t s . Thus, t h e s e and o t h e r as y e t u n i n v e s t i g a t e d s i t e s may be t a r g e t s f o r t h e s e n a t u r a l l y o c c u r r i n g compounds. Much more d a t a c o r r e l a t i n g m o l e c u l a r a c t i o n w i t h c h e m i c a l s t r u c t u r e w i l l be n e c e s s a r y t o f u l l y u t i l i z e the r a t i o n a l h e r b i c i d e design approach. C o r r e l a t i o n s o f mode o f a c t i o n d a t a o f s y n t h e t i c h e r b i c i d e s w i t h s l m i H a r m i c r o b i a l p h y t o t o x i n s t u d i e s s h o u l d y i e l d v a l u b l e new I n f o r m a t i o n t h a t c o u l d l e a d t o novel h e r b i c i d e s . Presently the molecular s i t e s of action o f many c u r r e n t l y marketed h e r b i c i d e s a r e known and d a t a on t h e i r p h y s i o l o g i c a l and b i o c h e m i c a l I n t e r a c t i o n s and secondary e f f e c t s i n p l a n t s 1s a c c u m u l a t i n g ( 3 1 . 2 9 0 - 2 9 3 ) . M i c r o b e s and M i c r o b i a l

P r o d u c t s as H e r b i c i d e s : O t h e r A s p e c t s

General C o n s i d e r a t i o n s . I f m i c r o b e s (pathogens) and m i c r o b i a l p r o d u c t s (from pathogens and non-pathogens) a r e t o be s u c c e s s f u l i n t h e commercial h e r b i c i d e a r e n a , s e v e r a l c r i t e r i a must be n e t . The p a t h o g e n i c o r g a n i s m must be h i g h l y v i r u l e n t , e c o n o m i c a l l y f e a s i b l e t o p r o d u c e , have an a c c e p t a b l e s h e l f - l i f e , and be e f f e c t i v e i n an range o f e n v i r o n m e n t a l c o n d i t i o n s . Some s u c c e s s w i t h pathogens has been made [ e x . C o l l e g o and DeVine (21)] and t h e r e a r e many p o t e n t i a l l y u s e f u l pathgens t h a t can c o n t r o l v a r i o u s weeds when a p p l i e d augmentâtively ( 2 9 4 - 2 9 6 ) . P r o d u c t i o n o f b i o h e r b i c l d e organisms ( s p o r e s , m y c e l i a ) can become a problem when s c a l i n g - u p from l a b o r a t o r y t o I n d u s t r i a l p r o d u c t i o n . With f u n g i (mycoherbi c i d e s ) problems o f p r o d u c t i o n a r e dependent on t h e growth h a b i t o f i n d i v i d u a l species (297). One o f t h e main problems i n t h i s a r e a w i t h r e g a r d t o f u n g a l pathogens 1s t h a t o f p r o v i d i n g p r o p e r e n v i r o n m e n t a l c o n d i t i o n s , e s p e c i a l l y a dew ( o r w a t e r ) p e r i o d which e n s u r e s s p o r e g e r m i n a t i o n and I n f e c t i o n ( o r I n f e c t i o n i f m y c e l i a l p r e p a r a t i o n s a r e a p p l i e d ) . With b a c t e r i a l weed pathogens, t h e problem 1s a g a i n m o i s t u r e and wounding. A second problem In pathogen f o r m u l a t i o n 1s g e t t i n g t h e o r g a n i s m t o adhere t o p l a n t s u r f a c e s . Some s u c c e s s f u l answers t o both t h e s e problems o f f o r m u l a t i o n have been made as summarized i n r e v i e w s ( 2 9 7 . 2 9 8 ) . A p p l i c a t i o n t e c h n o l o g y f o r m i c r o b i a l weed pathogens i s somewhat analagous t o h e r b i c i d e s u r f a c t a n t and a d d i t i v e t e c h n o l o g y ( 2 9 9 ) ; not t h a t t h e s e t e c h n o l o g i e s a r e a t t h e same s t a g e , but t h a t h e r b i c i d e p o t e n t i a l can be I n c r e a s e d w i t h t h e i r u s e . More c h e m i c a l r e s e a r c h w i l l be needed t o p r o v i d e f o r m u l a t i o n s f o r a p p l i c a t i o n o f pathogens f o r weed c o n t r o l .



Disrupted

Figure 6. Possible targets f o r herbicides, microbial p h y t o t o x i n s , and/or pathogens. (Based on a d i a g r a m i n R e f . 289. C o p y r i g h t 1974 Academic P r e s s and supplemented w i t h Information i n Refs. 290-292).

Growth and Reproduction

Structural Organization

I

Maior F u n c t i o n

Carotenoid Biosynthesis — * Destruction of Pigments (isoprenoid formation, desaturation, cylase, hydroxylation) Chlorophyll Biosynthesis — — — — — — — (porphorin core) Cell and Nuclear Division — — — — — — — (microtubule disruption) DNA, RNA, Protein Synthesis _ _ _ _ _ _ _ _ _ _ Interaction at IAA site _ _ _ _ _ _ _ _ _ _ _ _ _ Nitrogen Metabolism — — — — (ammonia incorporation, amino acid biosynthesis, nitrate/nitrite reduction, proline oxidation, polyamine biosynthesis) Cellulose Biosynthesis

Photoeynthetic Electron Transport Diverted Mitochondrial Electron Transport — ^ — Oxidative Phosphorylation Photoeynthetic Electron Transport (Hill Reaction) Carbon Metabolism

Membrane Integrity (membrane ATPaeee)

Lipid Biosynthesis — — — (fatty acide, wax formation)

Site pf Action



40


G e n e t i c and S t r a i n S e l e c t i o n o f M i c r o b i a l C a n d i d a t e s . As p r e v i o u s l y p r e s e n t e d , b i a l a p h o s and p h o s p h i n o t h r i c i n s t r a i n s e l e c t i o n t e c h n o l o g i e s , g e n e t i c t r a n s f o r m a t i o n , and f e r m e n t a t i o n methodology i s unsurpassed i n t h e m i c r o b i a l p r o d u c t i o n o f h e r b i c i d e s . These approaches s h o u l d be a p p l i e d t o some o f t h e more p r o m i s i n g m i c r o b i a l pathogens t o produce h i g h l y e f f i c a c i o u s weed pathogens o r t o m i c r o b e s f o r t h e o v e r p r o d u c t i o n o f p o t e n t t o x i n s f o r use as b i o h e r b i c i d e s . Some a s p e c t s r e g a r d i n g t h i s have been p r e s e n t e d (2QQ, 3 0 1 ) . Success i n p a t h o g e n i c i t y gene I s o l a t i o n and c l o n i n g (202, 221) and t r a n s f o r m a t i o n methodology (304) o f p l a n t pathogens w i l l e n s u r e major advances i n m i c r o b i a l b i o h e r b i c l d e t e c h n o l o g y . Advances i n t h e a r e a o f r e s t r i c t i n g h o s t range o f pathogens w i t h b r o a d - s p e c i f i c i t y have been made and a r e i n p r o g r e s s . The s e l e c t i o n o f a n o n - s c l e r o t i a l mutant o f S c l e r o t i n a s c l e r o t i o r i u m which i s a u b i q u i t o u s , n o n - s p e c i f i c pathogen has g r e a t u t i l i t y i n b i o h e r b i c i d e advances ( 3 0 5 ) . S t r a i n s e l e c t i o n and g e n e t i c m a n i p u l a t i o n can be time-consuming and t h e p a y - o f f may be u n c e r t a i n o r l o n g - t e r m . Biochemical/Chemical Cons1derat1ons. Biochemical a n a l y s i s o f p l a n t d e f e n s e mechanisms and o f pathogen I n f e c t i o n p r o c e s s e s have been e x t e n s i v e l y s t u d i e d f o r some t i m e , however t h e s e s t u d i e s have almost a l l been on c r o p p l a n t - p a t h o g e n I n t e r a c t i o n s . V a r i o u s enzymes a r e a c t i v e i n t h e s e I n t e r a c t i o n s (306) b u t , t h e s e p r o c e s s e s have e s s e n t i a l l y been n e g l e c t e d i n weed-pathogen s i t u a t i o n s . There i s a need t o examine such mechanisms i n weeds and m i c r o b i a l b l o h e r b l c i d e s so t h a t c h e m i c a l r e g u l a t o r s ( s p e c i f i c enzyme i n h i b i t o r s , h e r b i c i d e s , P G R ' s , e t c ) can be I d e n t i f i e d and used t o augment pathogen o r p h y t o t o x i n e f f i c a c y i n weed c o n t r o l . Such s t u d i e s s h o u l d o b v i o u s l y be c l o s e l y c o r r e l a t e d w i t h t o x i n and h e r b i c i d e mode o f a c t i o n ; even secondary h e r b i c i d e a c t i o n may p l a y major r o l e s i n r e g u l a t i o n o f pathogen e f f i c a c y . Conclusions The wide range o f c h e m i c a l c l a s s e s o f p h y t o t o x i n s from m i c r o b e s I n d i c a t e s t h a t m i c r o b i a l p r o d u c t s from p l a n t pathogens and nonpathogens a r e unique s o u r c e s f o r p o t e n t i a l b l o h e r b l c i d e s and as t e m p l a t e s f o r new s y n t h e t i c h e r b i c i d e s . However, s e v e r a l problems h i n d e r t h e i r f u l l development i n t o p r a c t i c a l weed c o n t r o l weapons. O f t e n , o n l y s m a l l amounts o f t h e s e new c h e m i s t r i e s have been i s o l a t e d , o r a r e 1 s o l a b l e , r e d u c i n g expanded r e s e a r c h by c o o p e r a t o r s i n o t h e r academic d i s c i p l i n e s and l i m i t i n g t h e s i z e o f b i o a s s a y and s c r e e n i n g programs. F u r t h e r m o r e , the unique c h e m i s t r i e s i n v o l v e d may not e a s i l y f i t i n t o commercial s y n t h e s i s programs; s y n t h e s i s r o u t e s may be d i f f i c u l t , time-consuming and c o s t l y . Fermentation p r o c e s s e s t o a c h i e v e l a r g e q u a n t i t i e s o f p h y t o t o x i n s o r organisms may be complex due t o the f a s t i d i o u s n a t u r e o f some o r g a n i s m s . F u r t h e r r e s e a r c h on t h e m o l e c u l a r mode o f a c t i o n , t h e a c t i v i t y s p e c t r u m , p e r s i s t e n c e , and n o n - t a r g e t e f f e c t s needs t o be accomplished. Cooperative e f f o r t s of chemists, biochemists, b i o l o g i s t s , p l a n t p a t h o l o g i s t s , and weed s c i e n t i s t s w i l l be r e q u i r e d t o a c h i e v e t h i s g o a l . P o l i t i c a l and s o c i a l a c c e p t a n c e o f t h i s new t e c h n o l o g y u s i n g t h e s e complex and dynamic agents ( m i c r o b e s ) as agents o f weed c o n t r o l w i l l a l s o be n e c e s s a r y ( 3 0 7 ) .


1. HOAGLAND

An Overview

41

Acknowledgments and D i s c l a i m e r s


M e n t i o n o f a t r a d e m a r k , p r o p r i e t a r y p r o d u c t , o r vendor does n o t c o n s t i t u t e a g u a r a n t e e o r w a r r a n t y o f t h e p r o d u c t by t h e U . S . Department o f A g r i c u l t u r e and does n o t i m p l y i t s a p r o v a l t o t h e e x c l u s i o n o f o t h e r p r o d u c t s o r vendors t h a t may a l s o be s u i t a b l e . T h i s c h a p t e r was p r e p a r e d by a U.S. Government employee as p a r t o f h i s o f f i c i a l d u t i e s and l e g a l l y cannot be c o p y r i g h t e d .

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MICROBES AND MICROBIAL PRODUCTS AS HERBICIDES Stierle, A.C.; Cardellina, J.H. Strobel G.A. Proc. Natl. Acad. Sci. 1988, 85, 8008-11. Dinoor, Α.; Eshed, N. Annu. Rev. Phytopathol. 1984, 22, 443-66. Charropadhyay, A.K.; Samaddar, K.R. Phytopathol. Z. 1980, 98, 118-26. Moore, W.F. Pl. Dis. Reptr. 1970, 54, 1104. Pena-Rodriguez, L.M.; Chilton, W.S. J . Nat. Prod. 1989, 52, 1170-2. Leung, P.C.; Taylor, W.A.; Wang, J.G.; Tipton, C.L. Pl. Physiol. 1985, 77, 303-8. Canales M.W.; Gray, G.R. Phytochemistry 1988, 27, 1653-63. Cutler, H.G.; Crumley, F.G.; Cox, R.H.; Springer, J.P.; Arrendale, R.F.; Cole, P.D. J . Agric. Food Chem. 1984, 32, 778-82. Robeson, D.; Strobel, G.; Matusumoto, G.K.; Fischer, E.L.; Chen, M.H.; Clardy, J . Experientia 1984, 40, 1248-50. Arnone, Α.; Nasini, G.; Merlini, L . ; Assiante, G. J . Chem. Soc. Perkin Trans. 1986, 1, 525-30. Sugawara, F.; Strobel, G.A. Phytochemistry 1987, 26, 1349-52. Fenn, P.; Durbin, R.D.; Kuntz, J.E. Phytochemistry 1977, 16, 899-901. Starratt, A.N. Can. J . Chem. 1968, 46, 767-70. Tietjen, K.G.; Schuller, E.; Matern, U. Physiol. Pl. Pathol. 1983, 23, 387-400. Gilchrist, D.G.; Grogen, R.G. Phytopathology 1976, 66, 165-71. Bottini, A.T.; Gilchrist, D.G. Tetrahed. Lett. 1981, 22, 2719-22. Bottini, A.T.; Bowen, J.R.; Gilchrist, D.G. Tetrahed. Lett. 1981, 22, 2723-6. Gilchrist, D.G. In Toxins and Plant Pathogenesis; Daly, J.M.; Deverall, B.J., Eds.; Academic Press: New York, 1983; pp. 81-136. Siler, D . J . ; Gilchrist, D.G. J . Chromatog. 1982, 238, 167-73. Kamata, S.; Sakai, H.; Hirota, A. Agric. Biol. Chem. 1983, 47, 2637-8. Nakashima, T.; Ueno, T.; Fukami, H. Tetrahed. Lett. 1982, 23, 4469-72. Suemitsu, R.; Yamada, Y.; Sano, T.; Yamahita, K. Agric. Biol. Chem. 1984, 48, 2383-4. Lee, S.; Aoyagi, H.; Shimohigashi, Y.; Izumiya, N.; Ueno, T.; Fukami, H. Tetrahed. Lett. 1976, 11, 843-6. Shimohigashi, Y.; Lee, S.; Kato, T.; Izumiya, N.; Ueno, T.; Fukami, H. Agric. Biol. Chem. 1977, 41, 1533-4. Kanmera, T.; Aoyagi, H.; Waki, M.; Kato, T.; Izumiya, N.; Noda, K.; Ueno, T. Tetrahed. Lett. 1981, 22, 3625-8. Yamada, O.; Kaise, Y.; Futatsuya, F.; Ishida, S.; Ito, K.; Yamamoto, H.; Munakata, K. Agric. Biol. Chem. 1972, 36, 2013-5. Murakata, K.; Yamada, O.; Ishida, S.; Futatsuya, F.; Ito, K.; Yamamoto, H. Proc. Asian Pacific Weed Sci. Conf. 1973, 4, 215-9.


1. HOAGLAND 106. 107. 108. 109. 110. 111. 112.


113. 114. 115. 116. 117. 118. 119. 120. 121. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134.

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46 135. 136. 137. 138. 139.


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Cutler, H.G.; Crumley, F.G.; Springer, J.P.; Cox, R.H. J . Agric. Food Chem. 1981, 29, 981-3. Ballio, Α.; Brutani, M.; Casinovi, G.G.; Cerrini, S.; Fedde, W.; Pellicciari, R.; Santurbano, B.; Vaclage, A. Experientia 1968, 24, 631-5. Chain, E.B.; Mantle, P.G.; Milborrow, B.W. Physiol. Pl. Pathol. 1971, 1, 495-514. Ballio, A. In Advances in Pesticide Science; Geisbühler, G., Ed.; Pergamon Press: Oxford, 1979; pp. 366-72. Kobayashi, K.; Miyazawa, S.; Terahara, Α.; Mishima, H.; Kurihara, H. Tetrahed. Lett. 1976, 537-40. Walsh, C.T. Ann. Rev. Biochem. 1984, 53, 493-535. Kannamgara, C.G.; Schouboe, A. Carlsberg Res. Commun. 1985, 50, 179-91. May, T.Β.; Guikema, J.A.; Henry, R.L.; Schuler, M.K.; Wong, P.P. Pl. Physiol. 1987, 84, 1309-13. Gardner, G.; Gorton, H.L. Pl. Physiol. 1985, 88, 540-3. Tchunmogne, S.J.; Huault, C.H.; Aoues, Α.; Balange, A.P. Pl. Physiol. 1989, 90, 1293-7. DeBoer, D.; Meulamn, P.Α.; Wnuk, R.J.; Peterson, D.H. J. Antibiot. 1970, 23, 442-7. DeBoer, D.; Dietz, A. J . Antibiot. 1976, 29, 1182. Iwai, Y.; Nakagawa, Α.; Sadakane, N.; Omura, S.; Oiwa, H.; Matzsumoto, S.; Takahashi, M.; Ikai, T.; Ochiai, Y. J. Antibiot. 1980, 33, 1114-9. Omura, S.; Iwai, Y.; Takahashi, M.; Sadakane, M.; Nakagawan, Α.; Oiwa, H.; Hasegawa, Y.; Ikai, T. J. Antibiot. 1979, 32, 255-61. Rinehart, K.L.; Sheild, L.S. Fortsch. Chem. Org. Naturst. 1976, 33, 231. Nishino, T.; Muraa, S. Agric. Biol. Chem. 1983, 47, 1961-6. Soper, T.S.; Manning, J.M. J . Biol. Chem. 1982, 257, 13930-6. Pringle, R.B.; Scheffer, R.P. Phytopathology 1967, 57, 1169-72. Pringle, R.B. Pl. Physiol. 1971, 48, 756-9. Macko, V. In Toxins and Plant Pathogenesis; Daly, J.D.; Deverall, B.J., Eds.; Academic Press: Australia, 1983; pp. 41-80. Walton, J.D.; Earle, E.D.; Gibson, B.W. Biochem. Biophys. Res.Commun.1982, 107, 785-94. Closse, Α.; Huguenin, R. Helv. Chem. Acta 1974, 57, 533-45. Stahelin, H.; Trippmacher, A. Eur. J . Cancer 1974, 10, 801-8. Arai, H.; Haneishi, T.; Kitahara, N.; Enokila, R.; Kawakuba, K.; Kondo, Y. J . Antibiot. 1976, 29, 863-9. Haneishi, T.; Terehara, Α.; Kayamori, H.; Yabe, J.; Aria, M. J . Antibiot. 1976, 29, 870-5. Tackiguchi, Y.; Yashikawa, H.; Terahara, Α.; Torikata, Α.; Terao, M. J . Antibiot. 1979, 32, 857-61. Tackiguchi, Y.; Yoshikama, H.; Terahara, Α.; Torikata, Α.; Terao, M. J . Antiobiot. 1979, 32, 862-7.


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1. HOAGLAND 281. 282. 283. 284. 285. 286.


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299. 300. 301. 302. 303. 304.

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