Plant Growth Substances - ACS Publications - American Chemical

10 Controlling Biological Behavior of Plants with Synthetic Plant Growth Regulating Chemicals

Downloaded by UNIV OF CINCINNATI on November 10, 2014 | http://pubs.acs.org Publication Date: September 27, 1979 | doi: 10.1021/bk-1979-0111.ch010

LOUIS G. NICKELL Research & Development, Velsicol Chemical Corporation, 341 E. Ohio Street, Chicago, IL 60611

Plant growth regulators usually are defined as organic compounds, other than nutrients, that, in small concentrations, affect the physiological processes of plants. For practical purposes, plant growth regulators can be defined as either natural or synthetic compounds that are applied directly to a plant to alter its life processes or structure in some beneficial way so as to enhance yields, improve quality, or facilitate harvesting. Herbicides, when applied to induce a specific beneficial change, also can be considered plant growth regulators. The response of a plant or a plant part to a plant growth regulator may vary with the variety of plant. Even a single variety may respond differently, depending on its age, environmental conditions, physiological state of development (especially its natural hormonal content), and its state of nutrition. Thus, whenever a general rule is suggested concerning the action of a specific growth regulator on plants, exceptions almost always can be found. Uses of Growth Regulants The regulation of plant growth can be economically useful in a great many ways. Among other things, it can: Promote r o o t i n g and propagation of the p l a n t . I n i t i a t e or terminate the dormancy of seeds, buds, and tubers. Induce or r e t a r d aging (senescence). Promote, d e l a y , or prevent f l o w e r i n g . Induce or prevent l e a f and/or f r u i t drop ( a b s c i s s i o n ) . C o n t r o l f r u i t set and f u r t h e r f r u i t development. C o n t r o l p l a n t or organ s i z e . Prune the plant c h e m i c a l l y . 0-8412-0518-3/79/47-lll-263$05.00/0 © 1979 American Chemical Society

In Plant Growth Substances; Mandava, N.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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Modify sex expression. Increase p l a n t r e s i s t a n c e to p e s t s . Enhance p l a n t r e s i s t a n c e to such environmental f a c t o r s as temperature, water, and a i r p o l l u t i o n . Prevent postharvest s p o i l a g e . Regulate the chemical composition of p l a n t s and the c o l o r of f r u i t . Influence m i n e r a l uptake from the s o i l . Change the timing of crop development C o n t r o l weeds. As f a r back as the 1940 s, chemicals that we now c l a s s i f y as plant growth r e g u l a t o r s were used experimentally to root c u t t i n g s and to promote flowering i n p i n e a p p l e . The f i r s t important commercial a p p l i c a t i o n of a p l a n t growth r e g u l a t o r was i n the 1 9 4 0 s , when naphthalene a c e t i c a c i d was a p p l i e d , as i t s t i l l i s , to prevent the preharvest drop of a p p l e s . One of the o l d e s t and best known uses f o r p l a n t growth r e g u l a t o r s has been i n i n i t i a t i n g and/or a c c e l e r a t i n g the r o o t i n g of c u t t i n g s . One of the best chemicals f o r t h i s purpose i s i n dolebutyric acid. This compound i s decomposed r e l a t i v e l y slowly by the hormone d e s t r o y i n g enzyme systems i n p l a n t s . Because the chemical a l s o moves very slowly i n the p l a n t , much of i t i s r e tained near the s i t e of a p p l i c a t i o n - another d e s i r a b l e c h a r a c t eristic. Although a host of other chemicals have been evaluated for t h e i r e f f e c t on r o o t i n g , and some of them have d e s i r a b l e a c t i o n s , i n d o l e b u t y r i c a c i d s t i l l remains the compound of choice for t h i s purpose. In the e a r l y 1 9 5 0 s , 1 , 2 - d i h y d r o - 3 , 6 - p y r i d a z i n e d i o n e (maleic hydrazide) was f i r s t marketed to prevent the s p r o u t i n g of onions i n storage. Soon a f t e r , maleic hydrazide a l s o was used to i n h i b i t t u r f growth and prevent the s p r o u t i n g of potatoes during storage.


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C o n t r o l l i n g Flowering Pineapple. In the l a t e 1 9 2 0 s , s c i e n t i s t s found that the long-recognized f a c t that pineapple could be forced to flower by smoke from f i r e s (used to prevent growth from stopping during c o l d weather) was caused by i t s content of unsaturated gases, such as ethylene. By the mid-1930 s, acetylene gas was used commercially i n Hawaii to force the i n i t i a t i o n of f l o w e r i n g . L a t e r , p l a n t hormones were shown to produce t h i s e f f e c t , and 1-naphthaleneacetic a c i d was the next f o r c i n g agent to be used commercially on p i n e a p p l e s . Although hydrazines are more commonly thought of as growth r e t a r d a n t s , s e v e r a l of them, e s p e c i a l l y B-hydroxyethylhydrazine, were shown i n the mid-1950 s to induce flowering i n Hawaiian pineapples by Dr. Donald P. Gowing and Dr. Robert W. Leeper at the Pineapple Research I n s t i t u t e (1). The l a t e s t group of compounds demonstrated to be e f f e c t i v e f o r c i n g agents f o r pineapples are the haloethanephosphonic a c i d s f

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Synthetic Plant Growth Regulators

such as ethephon. duce t o t a l f l o r a l

Levels of 1 to 2 l b of ethephon per acre p r o induction.


F r u i t Trees. In many f r u i t t r e e s , e s p e c i a l l y a p p l e , pear, and peach, the the extent of f l o r a l i n d u c t i o n i s increased by spraying them with i n h i b i t o r s such as s u c c i n i c a c i d - 2 , 2 - d i m e t h y l hydrazine (sold by U n i r o y a l as A l a r ) and 2 , 3 , 5 - t r i i o d o b e n z o i c a c i d . Vegetables. Many annual v e g e t a b l e s , such as l e t t u c e , r a d i s h , mustard, and d i l l , which normally flower only when days are l o n g , can be made to flower e a r l y by treatment with g i b b e r e l l i n s . Many b i e n n i a l v e g e t a b l e s , such as c a r r o t s , beets, and cabbage, which r e q u i r e low temperatures to flower, a l s o do so a f t e r treatment with g i b berellins. Sugarcane. To improve the y i e l d s of some c r o p s , such as sugarcane, i t i s commercially d e s i r a b l e to prevent f l o w e r i n g . In other c r o p s , among them almond, peach, and tung o i l t r e e s , a delay i n the onset of flowering may be d e s i r a b l e to avoid adverse weather cond i t i o n s , such as extremes i n temperature and moisture. Such a delay a l s o can b r i n g two p l a n t v a r i e t i e s w i t h d i f f e r e n t flowering dates i n t o s y n c h r o n i z a t i o n for breeding purposes (as i n the case of v a r i e t i e s of almond t r e e s ) or c o n t r o l the timing of flowering of p l a n t s such as c a r n a t i o n or p o i n s e t t i a to c o i n c i d e with major h o l i d a y s , when s e l l i n g p r i c e s are h i g h e r . Fundamental s t u d i e s of flowering i n a l a r g e v a r i e t y of p l a n t s have shown that nighttime length i s the c r i t i c a l f a c t o r i n many cases. Sugarcane belongs to a group of short-day p l a n t s that i n i t i a t e flowers only w i t h i n a c r i t i c a l range of day-lengths (2). Members of t h i s group must have an u n i n t e r r u p t e d dark p e r i o d i f they are to flower. The b r i e f e s t i n t e r r u p t i o n (for sugarcane as l i t t l e as 50 foot-candle-minutes of incandescent l i g h t ) i s u s u a l l y s u f f i c i e n t to prevent f l o w e r i n g . D r . George 0. Burr and h i s colleagues at the Hawaiian Sugar P l a n t e r s A s s o c i a t i o n Experiment S t a t i o n determined i n the mid-1950 s that night i n t e r r u p t i o n from Sept 1 to 20 would i n h i b i t flowering of the sugarcane v a r i e t i e s propagated i n Hawaii at that time. F i e l d experiments l a t e r showed that suppression of flowering r e s u l t e d i n increases i n the y i e l d of sucrose averaging 1.3 tons per a c r e . 1

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In the years immediately f o l l o w i n g these s t u d i e s , the f a c t o r s a f f e c t i n g f l o w e r i n g , as w e l l as methods f o r preventing i t , were studied e x t e n s i v e l y . Several methods were found to be e f f e c t i v e i n preventing f l o w e r i n g : i n t e r r u p t i n g night with l i g h t , lowering temperature, l e a f and s p i n d l e trimming, withdrawing water, or a p p l y i n g chemicals. Because temperature cannot be c o n t r o l l e d i n the f i e l d and because l e a f trimming and l i g h t i n t e r r u p t i o n on a commercial s c a l e are not economically f e a s i b l e , emphasis has


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been placed on water withdrawal and the a p p l i c a t i o n of chemicals. Withdrawal of water i s p o s s i b l e only on i r r i g a t e d p l a n t a t i o n s . Because t h i s p r a c t i c e causes v a r i o u s o p e r a t i o n a l problems, the use of chemicals e v e n t u a l l y became the standard p r a c t i c e i n Hawaii. Maleic hydrazide was the f i r s t p o t e n t i a l l y u s e f u l commercial chemical f o r preventing the flowering of sugarcane b u t , at b e s t , i t gave only about 60% c o n t r o l . Rapid developments i n the 1950 s l e d to the use of 3 - ( p - d i c h l o r o p h e n y l ) - l , l - d i m e t h y l u r e a (monuron) as the chemical of choice and l a t e r to the use a l s o of 3 - ( 3 , 4 dichlorophenyl)-l,1-dimethylurea (diuron). When p r o p e r l y a p p l i e d , 4 l b per acre of e i t h e r chemical provides v i r t u a l l y complete c o n t r o l of flowering i n the h e a v y - t a s s e l i n g cane v a r i e i t e s used i n the 1950*s and e a r l y I960 s i n Hawaii, Continued t e s t i n g f o r more a c t i v e chemicals to prevent flowe r i n g l e d the l a t e Tyrus T. Tanimoto and me to the discovery i n the e a r l y 1960 s that 6 , 7 - d i h y d r o d i p y r i d o ( 1 , 2 - a : 2 ' , 1 - c ) p y r a z i d i n i u m dibromide ( d i q u a t ) , i s a c t i v e at r a t e s of 0.125 l b per acre. Thus, t h i s newer chemical i s one of the most a c t i v e compounds yet used f o r t h i s purpose. The cost of c o n t r o l l i n g f l o w e r i n g , per u n i t a r e a , i s decreased a s u b s t a n t i a l 70%. The compound a l s o has been found to be h i g h l y e f f e c t i v e i n preventing the flowering of sugarcane i n Guyana, Mexico, the P h i l i p p i n e s and Taiwan, i n a d d i t i o n to Hawaii (3).


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Controlling Abscission The c o n t r o l of a b s c i s s i o n , (the separation of shedding of a p l a n t p a r t , such as a l e a f , flower, f r u i t , or stem from the parent p l a n t ) i s extremely important i n a g r i c u l t u r e . To ensure the most e f f e c t i v e crop growth, leaves should be r e t a i n e d i n a h e a l t h y , green s t a t e . On the other hand, to s i m p l i f y the mecha n i c a l h a r v e s t i n g of c e r t a i n crops, such as c o t t o n , i t i s h i g h l y d e s i r a b l e to have the leaves removed. The same i s true f o r f r u i t In t r e e crops that have a l a r g e number of f r u i t s t a r t e d , i t i s sometimes d e s i r a b l e to t h i n the f r u i t by using an a b s c i s s i o n inducing compound, thereby i n c r e a s i n g the s i z e and q u a l i t y of the remaining f r u i t . During crop growth, the f r u i t should be r e t a i n e d on the t r e e f o r maximum development and m a t u r i t y . However, at h a r v e s t , f o r many i f not most c r o p s , the use of an abs c i s s i o n - i n d u c i n g agent can be h i g h l y p r o f i t a b l e i n reducing labor requirements and c o s t s . T h i s i s p a r t i c u l a r l y true of citrus. Citrus. An a c t i v e a b s c i s s i o n research program f o r c i t r u s has been underway f o r a number of years i n F l o r i d a by the F l o r i d a State C i t r u s Commission i n c o l l a b o r a t i o n with a number of chemical companies. T h i s program was i n i t i a t e d o r i g i n a l l y because of a shortage of labor f o r handpicking c i t r u s . Chemicals to speed up the removal of f r u i t by mechanical harvesters and to increase


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the p r o d u c t i v i t y of handpickers have been developed ( 4 ) « The a c t i v e compounds used e a r l i e s t were termed "mass a c t i o n " compounds because they were a p p l i e d at high r a t e s (up to 100 l b per a c r e ) . Unfortunately at these l e v e l s , the chemicals damaged both the f r u i t and the t r e e . The f i r s t breakthrough came when the a n t i f u n g a l a n t i b i o t i c 3 - ( 2 - Q 3 , 5 - d i m e t h y l - 2 - o x o c y c l o h e x y l 3 - 2 - h y d r o x y e t h y l ) g l u t a r i m i d e (cycloheximide or Upjohn s A c t i Aid) was found to loosen c i t r u s f r u i t s at a p p l i c a t i o n r a t e s of l e s s than 0 . 1 l b per acre ( 5 ) . Although cycloheximide i s used commercially i n F l o r i d a on most orange v a r i e t i e s , i t i s not used during the h a r v e s t i n g of V a l e n c i a oranges because i t damages the flowers and the immature f r u i t . For a long time, e f f o r t s to f i n d s u i t a b l e a b s c i s s i o n chemicals f o r V a l e n c i a oranges faced a number of problems. Recently, a s e l e c t i v e a b s c i s s i o n m a t e r i a l , 5 - c h l o r o - 3 - m e t h y l - 4 n i t r o - l H p y r a z o l e (Abbott's Release), has been developed that e f f e c t i v e l y induces a b s c i s s i o n i n mature f r u i t without damaging new twig growth and immature f r u i t ( 6 ) .


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Olives. Man-power a v a i l a b i l i t y f o r o l i v e p i c k i n g i s becoming an i n c r e a s i n g problem f o r o l i v e growers. Considerable research i s being c a r r i e d out i n the Mediterranean r e g i o n and i n C a l i f o r n i a , the main goal of which i s to decrease the amount of l a b o r needed for o l i v e h a r v e s t i n g . E f f o r t s to decrase l a b o r consumption are d i r e c t e d toward a mechanical s o l u t i o n , a chemical s o l u t i o n , or a combination of both. It has been known f o r some time that ethephon i s one of the best compounds f o r decreasing the f r u i t removal f o r c e needed to f a c i l i t a t e o l i v e h a r v e s t i n g . More r e c e n t l y a new m a t e r i a l , A l s o l [ 2 - c h l o r o e t h y l - t r i s - ( 2 - m e t h o x y ethoxy) s i l a n e ] , has been developed which i s more e f f e c t i v e f o r t h i s purpose than ethephon. However, buffered ethephon can be used to f a c i l i t a t e a r a p i d , easy and r e l a t i v e l y inexpensive harvest of o l i v e s . Now growers have two chemicals of s i m i l a r e f f i c i e n c y to choose between. The data so f a r i n d i c a t e that t h i s d e c i s i o n w i l l be based on economic c a l c u l a t i o n s ( 7 ) . Cotton We a l l know of the o l d p r a c t i c e of " p i c k i n cotton" - h a r v e s t i n g cotton b o l l s by hand. In g e n e r a l , t h i s p r a c t i c e has been r e p l a c e d by machine h a r v e s t e r s . Since i n t r o d u c t i o n of the harvest machine, use of chemical a i d s has become common-place. Cotton leaves are d e f o l i a t e d by chemical harvest a i d s on more than 75% o f the cotton acreage i n the U . S . - r e p r e s e n t i n g more than 7 m i l l i o n acres of c o t t o n . H i s t o r i c a l l y cotton b o l l s have been harvested by hand. More r e c e n t l y , however, the development of machine harvesters has reduced p r o d u c t i o n c o s t s . For e f f i c i e n t use of both types of p i c k e r s (the s p i n d l e type with r o t a t i n g s p i n d l e s that p i c k s the cotton only from open b o l l s , and the s t r i p p e r type which s t r i p s f



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the e n t i r e p l a n t except the main stems) most of the f o i l a g e must be removed before h a r v e s t . T h i s has been accomplished f o r sometime by h a r v e s t - a i d p r a c t i c e s c o n s i s t i n g of c h e m i c a l l y t r e a t i n g the cotton p l a n t at the proper time to induce d e f o l i a t i o n before harvest. Chemical harvest a i d s are p r e s e n t l y used on more than 75% of the cotton acreage i n the U . S . . The amount of f o l i a g e may be reduced e i t h e r by the use of d e f o l i a n t s or the use of d e s i c c a n t s . D e f o l i a n t s induce l e a f f a l l and must be a p p l i e d one to two weeks before harvest so that the a b s c i s s i o n process may be complete. Desiccants cause the f o l i a g e to l o s e water and sometimes the leaves and stems are k i l l e d so r a p i d l y by d e s i c c a n t s that an a b s c i s s i o n l a y e r has i n s u f f i c i e n t time to develop and the d r y i n g leaves remain attached to the p l a n t . Desiccants u s u a l l y r e q u i r e one to three days to act before harvest can be s t a r t e d . The obvious advantage of desiccants over d e f o l i a n t s i s that they may be a p p l i e d at a l a t e r date, thus g a i n i n g a d d i t i o n a l time during which the l'eaves continue to f u n c t i o n and to c o n t r i b u t e to see the f i b e r q u a l i t y . Hundreds of chemicals have been evaluated as d e f o l i a n t s and d e s i c c a n t s . Only a few are i n commercial use. The best known of these d e f o l i a n t s are sodium c h l o r a t e which has the danger of s t a r t i n g f i r e s , t r i b u t y l - p h o s p h o r o t r i t h i o i t e (merphos, Folex) i t s oxygenated r e l a t i v e t r i b u t y l p h o s p h o r o t r i t h i o i t e (DEF), and e n d o t h a l l ( A c c e l e r a t e ) . Recent research r e p o r t s c l a i m that amino methyl phosphonic a c i d and c e r t a i n of i t s r e l a t i v e s were found to be more a c t i v e than current commercial products. The best known desiccant used f o r d e f o l i a t i o n of c o t t o n i s paraquat ( 1 , l - d i m e t h y l - 4 , 4 - b i p y r i d i n i u m ) (8). ?

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Fruit. The t h i n n i n g of f r u i t on v a r i o u s specied of f r u i t trees and grapes i s necessary commercially. Because t h i s i s d i f f i c u l t and c o s t l y to do by hand, however, growers have turned to the use of chemicals. Chemicals have been used to t h i n f r u i t set i n a p p l e s , for example, since the e a r l y 1930's. In a d d i t i o n to p e r m i t t i n g crops to be produced annually be e l i m i n a t i n g or reducing a l t e r nate-year b e a r i n g , t h i s p r a c t i c e a l s o enhances the s i z e , c o l o r and q u a l i t y of the f r u i t . Of the e a r l y compounds used f o r t h i s purpose, the most impo r t a n t was 1-naphthaleneace'tic a c i d and i t s amide. More r e c e n t l y , ethephon has shown promise as a t h i n n i n g agent. 3-Chlorophenoxy- propionamide has produced good t h i n n i n g i n s e v e r a l v a r i e t i e s of peach. Both g i b b e r e l l i c a c i d and ethephon are e f f e c t i v e t h i n n i n g agents f o r grapes. The preharvest drop of c i t r u s f r u i t can be reduced or prevented with 2,4-dichlorophenoxyacetic a c i d , which delays development i n the a b s c i s s i o n zone of the f r u i t stem, thus a l l o w i n g the f r u i t to remain on the t r e e l o n g e r . Because of 2 , 4 - D s h e r b i c i d a l p r o p e r t i e s , however, care must be taken i n spraying to prevent the chemical from damaging other c r o p s , as w e l l as the target crop f


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itself. C o n t r o l of F r u i t Development In recent years, s c i e n t i s t s have found that many s y n t h e t i c growth r e g u l a t o r s w i l l develop f r u i t i n p l a n t s . The best of these a r e 4-chlorophenoxyacetic a c i d and 2-naphthoxyacetic a c i d . These chemicals are most e f f e c t i v e on f r u i t s that have many ovules, such as tomato, squash, egg-plant, and f i g . They are u s u a l l y r a t h e r i n e f f e c t i v e , however, on peach, cherry, plum, and other stone f r u i t s . Many f r u i t s that can be s e t by such hormonal compounds a l s o can be set by the g i b b e r e l l i n s . In a d d i t i o n , g i b b e r e l l i n s can s e t f r u i t i n some species that do not respond to the other chemicals. In the San Joaquin V a l l e y , s e v e r a l grape v a r i e t i e s y i e l d much below the v i n e c a p a c i t y because of poor f r u i t s e t . Y i e l d of Malvasia blanca grapes was more than doubled by pre-bloom spray of the plant growth r e g u l a t o r Cycocel (chlormequat). The increase of 4.4 tons per acre (20 pounds per v i n e ) was p r i m a r i l y due to improved berry set. C l u s t e r s from t r e a t e d v i n e s were w e l l f i l l e d ; those from the c o n t r o l l e d v i n e s were loose and s t r a g g l y , with some c l u s t e r s s e t t i n g no f r u i t at a l l . To date, Cycocel has not been r e g i s t e r e d f o r t h i s use ( 9 ) . Experiments i n A u s t r a l i a show advantages i n spraying prune trees before harvest with s e l e c t e d growth r e g u l a t i n g chemicals. This has been done over a p e r i o d of four years and recent r e ports suggest s i g n i f i c a n t f i n a n c i a l b e n e f i t s from the use of growth r e g u l a t o r s . The recommendations a r e f o r use of gibbere l l i c a c i d at 10 ppm or napthalene a c e t i c a c i d at 20 ppm y i e l d i n g an e x t r a $260.00 per hectare (10,11). Gibberellins I n f e c t i o n of r i c e by the fungus G i b b e r e l l a f u j ikuroa, causing the elongated " f o o l i s h s e e d l i n g " e f f e c t , has been known f o r generations. Not u n t i l 1938, however, was a c r y s t a l l i n e fungal metabolite i s o l a t e d as the c a u s a t i v e agent at the Univers i t y of Tokyo by Dr. T e i j i r o Yabuta and Dr. Yusuke Sumimi. T h e i r work l e d to the discovery of a new c l a s s of hormones, the gibberellins. Because of wartime secrecy, l i t t l e was published about these new "wonder compounds" u n t i l the 1950 s, when t h e i r spectacular e f f e c t s on both ornamental and e d i b l e crop p l a n t s r e c e i v e d enormous p u b l i c i t y . In most p l a n t s , the outstanding e f f e t of the g i b b e r e l l i n s i s to elongate the primary s t a l k . This e f f e c t occurs i n the young t i s s u e s and growth centers and i s caused e i t h e r by an increase i n c e l l ' length, an increase i n the r a t e of c e l l d i v i s i o n , or a combination of both, depending on the s p e c i f i c type of plant treated. G i b b e r e l l i n s can induce flowering i n many plant s p e c i e s , such as c a r r o t s , that r e q u i r e low temperatures to i n i t i a t e t h i s process. The a b i l i t y of a chemical to promote f l o w e r i n g i s f



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v a l u a b l e both i n c o n t r o l l i n g the timing of flowering to match h o l i d a y markets and f o r the p r o d u c t i o n of seed. G i b b e r e l l i n s have remarkable e f f e c t s on many dwarf p l a n t s , such as dwarf pea, dwarf c o r n , and bush beans. When t r e a t e d with g i b b e r e l l i n s , these p l a n t s grow to f u l l s i z e . Gibberellins a l s o a f f e c t the extent to which a p l a n t develops s i d e branches. In a d d i t i o n , they increase the s i z e of many young f r u i t s , expec i a l l y grapes. Because g i b b e r e l l i n s induce the production of the enzyme amylase i n b a r l e y , they a l s o are commonly used i n the malting of b a r l e y . At p r e s e n t , the biggest uses of g i b b e r e l l i n s are i n i n c r e a s ing the s i z e o f grapes and i n s t i m u l a t i n g the growth of sugarcane. Treatment of sugarcane with as l i t t l e as 2 oz of g i b b e r e l l i n per acre increases the y i e l d of cane more than 5 tons per acre and r a i s e s the output of sugar 0.2 to 0.5 ton per a c r e . G i b b e r e l l i n s are used i n grapes f o r s e v e r a l d i f f e r e n t p u r poses. The present commercial p r a c t i c e i n C a l i f o r n i a i s to spray twice, once at bloom f o r a loosening and s i z i n g e f f e c t and again at f r u i t - s e t stage f o r an a d d i t i o n a l s i z i n g e f f e c t . Although g i b b e r e l l i n s have been used on a small s c a l e for over a decade i n Hawaii (12,13), i t was not u n t i l 1976 that one of the sugar p l a n t a t i o n s on the i s l a n d of Oahu u t i l i z e d g i b b e r e l l i n s on a l a r g e commercial s c a l e and a l s o s t u d i e s the i n t e r a c t i o n with ripeners. The t e s t r e s u l t s show that treatments of s p l i t a p p l i c a t i o n s of g i b b e r e l l i n s i n combination with a chemical r i p e n e r gave the best response. The o v e r a l l y i e l d comparisons throughout the e n t i r e season were based on 42 f i e l d blocks of approximately 40 acres each, i n 18 d i f f e r e n t l o c a t i o n s . An increase of 5% i n t o t a l crop t o n nage i s c r e d i t e d to t h i s program. The economic b e n e f i t of t h i s program f o r the a p p l i c a t i o n of growth r e g u l a t o r s has been c o n siderable. An o u t l a y of $200,000 f o r g i b b e r e l l i n s and the r i pener P o l a r i s f o r t h i s one p l a n t a t i o n during 1976 added over 3,500 tons of sugar to the crop at a cost of about $60 per ton of sugar produced. This sugar reduced the average p r o d u c t i o n cost by n e a r l y $10 per ton and returned approximately $400,000 net p r o f i t a f t e r taxes to the p l a n t a t i o n for 1976 (14). The g i b b e r e l l i n s a l s o have been t e s t e d on a wide range of vegetable c r o p s , w i t h r e s u l t s to date that are s p e c t a c u l a r but often not b e n e f i c i a l . For example, i n many s p e c i e s , such t r e a t ment can induce premature f l o w e r i n g , which i s u n d e s i r a b l e i n crops such as cabbage, s i n c e i t i s the v e g e t a t i v e leaves that are commercially v a l u a b l e . C o n t r o l of P l a n t S i z e A p l a n t growth r e g u l a t o r that reduces stem length i n c e r e a l c r o p s , 2 - c h l o r o e t h y l trimethylammonium c h l o r i d e (American Cyanamid's Cycocel) has become an important f a c t o r i n farming, e s p e c i a l l y i n growing of wheat. T h i s compound prevents, or at l e a s t g r e a t l y reduces, the p o s s i b i l i t y that wheat w i l l "lodge"



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( f a l l over i n heavy winds and r a i n ) . About h a l f of the wheat grown i n West Germany, f o r example, i s t r e a t e d with C y c o c e l . In f a c t , that c o u n t r y ' s increased y i e l d of wheat i n recent years i s l a r g e l y a t t r i b u t e d to t h i s plant growth r e g u l a t o r . Dr. Sylvan H. Wittwer, d i r e c t o r of the Michigan A g r i c u l t u r a l Experiment S t a t i o n , says that the use of Cycocel e l i m i n a t e s the need f o r g e n e t i c a l l y developed l o d g i n g - r e s i s t a n t v a r i e t i e s of wheat. Treatment with Cycocel produces a s h o r t e r p l a n t w i t h t h i c k e r stems, greener l e a v e s , more s i d e shoots, and b e t t e r f i l l e d heads. Cycocel i s among the most widely used p l a n t growth r e g u l a t o r s i n the world (15). Mowing t u r f grass i s a time consuming and c o s t l y maintenance procedure both for p r o f e s s i o n a l t u r f managers and f o r homeowners. The use of p l a n t growth r e g u l a t o r s to i n h i b i t grass growth has been a p r a c t i c e f o r y e a r s . T h i s approach has been of c o n s i d e r able i n t e r e s t both to i n d u s t r y and to landscape maintenance people. Maleic hydrazide ) 1 , 2 - d i h y d r o - 3 , 6 - p y r i d a z i n e d i o n e , (MH) has been u t i l i z e d f o r 20 years i n grass growth r e g u l a t i o n . More r e c e n t l y c h l o r f l u r e n o l and m e f l u i d i d e (Embark) have been shown to e x h i b i t c o n s i d e r a b l e p o t e n t i a l i n the c o n t r o l of a number of grasses. The plant growth r e g u l a t o r 1,1-dimethyl p i p e r i d i n i u m c h l o r i d e can be used to manage the v e g e t a t i v e development of cotton p l a n t s to o f f s e t the e f f e c t of excessive r a i n water or n i t r o g e n by decreasing both o v e r a l l p l a n t height and length of l a t e r a l branches. T h i s maintains a p l a n t form which can f a c i l i t a t e crop p r o t e c t i o n and mechanical h a r v e s t i n g p r a c t i c e s . The use of t h i s same m a t e r i a l at r a t e s lower than that to i n h i b i t s i z e of plant causes increases i n y i e l d which appears to be p a r t l y due to l e s s shedding of flowers and/or b o l l s , increases i n b o l l weight, and number of open b o l l s at h a r v e s t . Modify Sex Expression Because they can a f f e c t both the determination of sex and the time of f l o w e r i n g , growth r e g u l a t o r s now are commonly used to a i d i n seed production i n vegetables and i n the breeding of s e v e r a l types of crops. Crops whose sex has been manipulated through growth r e g u l a t o r s i n c l u d e begonia, c o t t o n , cucumber, grape, hops, pumpkin, squash, and tomato. Biochemistry and C e l l Biology For more than two decades, maleic hydrazide has been used e x t e n s i v e l y on tobacco to prevent the formation of suckers ( a u x i l i a r y buds), which decrease l e a f q u a l i t y . Before t h i s m a t e r i a l was developed, l a r g e amounts of hand l a b o r were r e quired to remove the buds. T h i s use f o r maleic hydrazide i s one of the great success s t o r i e s i n the plant growth r e g u l a t o r field.



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Chemical p i n c h i n g of azaleas has been p r a c t i c e d commercially for many y e a r s . A number of compounds are now a v a i l a b l e f o r use i n the chemical pruning of azaleas and other p l a n t s . One of these i s methyldecanoate (sold under the trade name O f f Shoot-O) (16). Recently i t has been shown that a p i c a l dominance can be s u c c e s s f u l l y overcome with the proper a p p l i c a t i o n of the chemical d i k e g u l a c . The savings i n labor and accompanying costs are s u b s t a n t i a l with the use of the chemical p i n c h i n g or chemical pruning (17). A group of diphenyl ethers has r e c e n t l y been reported as being e f f e c t i v e i n c o n t r o l l i n g u n d e s i r a b l e sucker growth i n tobacco and u n d e s i r a b l e secondary growth i n general i n a number of p l a n t s . The i n h i b i t i o n of bud growth has been shown a l s o to be accomplished by s u b s t i t u t e d 2 , 6 dinitroanalines. An understanding of the postharvest physiology of p l a n t t i s s u e s i s of great importance because of the l a r g e s p o i l a g e l o s s e s caused by plant o v e r r i p e n i n g and a g i n g . For many y e a r s , some s c i e n t i s t a have b e l i e v e d that the d e t e r i o r a t i o n of a crop i f a s s o c i a t e d with the a c t i o n of the ethylene that the p l a n t produces i n t e r n a l l y . A more up-to-date concept i s that aging i n p l a n t t i s s u e s i s not only a d e t e r i o r a t i v e process but a l s o a developmental process i n which growth r e g u l a t o r s besides ethylene play important r o l e s . As Dr. M o r r i s Lieberman, head of the post-harvest plant physiology l a b o r a t o r y at USDA's A g r i c u l t u r a l Research Center i n B e l t s v i l l e , MD., says, "Although ethylene i s s t i l l considered a major i n f l u e n c e on postharvest metabolism, the other p l a n t hormones - the a u x i n s , g i b b e r e l l i n s , c y t o k i n i n s , and a b s c i s i c a c i d - a l s o are thought to s i g n i f i c a n t l y i n f l u e n c e the aging process. Most l i k e l y , ethylene a c t i o n r e s u l t s from i n t e r a c t i o n s with these hormones" (18). Today, another e x c i t i n g research area involves the b i o r e g u l a t i o n of p l a n t composition. Such b i o r e g u l a t i o n i s the process of c o n t r o l l i n g s p e c i f i c metabolic pathways (or a s e r i e s of such pathways) by e x t e r n a l l y s u p p l i e d s y n t h e t i c chemicals. These b i o r e g u l a t o r s are low-molecular-weight compounds, i n c o n t r a s t to the high-molecular-weight b i o l o g i c a l polymers (proteins and n u c l e i c a c i d s ) through which the s y n t h e t i c b i o r e g u l a t o r s appear to exert t h e i r c o n t r o l on metabolism. Bior e g u l a t i o n i s more than j u s t a t h e o r e t i c a l approach; a l r e a d y , c o l o r i n c i t r u s and tomatoes and v i t a m i n content i n a number of vegetables and f r u i t s has been c o n t r o l l e d and the sugar y i e l d i n the cane plant i n c r e a s e d . Several companies, i n cooperation with the U . S . Forest S e r v i c e , have been studying the e f f e c t i v e n e s s of paraquat i n enhancing the q u a n t i t y of chemicals produced i n s l a s h and l o b l o l l y pine t r e e s . Results over the l a s t 6 years show that there can be a p o s i t i v e e f f e c t and that beta-pinene i s p r e f e r e n t i a l l y produced i n s l a s h pines by treatment with paraquat. Results reported on l o b l o l l y pine show an i n c r e a s e of 50% i n t a l l o i l content when c o r r e c t l y a p p l i e d . The expected i n c r e a s e



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i s promising enough that most companies i n v o l v e d are c o n t i n u i n g t h e i r e f f o r t s with t h i s approach. Growth r e g u l a t o r s can i n f l u e n c e a p l a n t ' s a b s o r p t i o n of minerals from the s o i l . The uptake of potassium by wheat, f o r example, i s a c c e l e r a t e d by t r e a t i n g the p l a n t with g i b b e r e l l i c acid. The uptake of both n i t r o g e n and phosphorus by wheat and soybean p l a n t s i s enhanced by treatment with 2 , 4 - D . There are a number of recent r e p o r t s from the Russion l i t erature on the i n c r e a s e of corn y i e l d s through weed c o n t r o l by a t r a z i n e and 2,4-D amine. Although they do not d i s t i n g u i s h between weed c o n t r o l and i t s s p e c i f i c p o s i t i v e e f f e c t s on y i e l d , they c l e a r l y show increased uptake of n u t r i e n t s i n the absence of weeds (19). Growth r e t a r d a n t s have been found to i n c r e a s e the drought r e s i s t a n c e of a number of p l a n t s . The mechanism by which growth r e t a r d a n t s accomplish t h i s i s not known. However, the e f f e c t of Cycocel and SADH i n i n c r e a s i n g the a b i l i t y of a p l a n t to withstand drought i s thought to be r e l a t e d to the a b i l i t y of these chemicals to delay the senescence of detached l e a v e s . A l s o , i n the case of b r u s s e l s p r o u t s , treatment by Cycocel r e duces the number of stomata per u n i t area which could decrease the r a t e of water l o s s from the l e a f and c o n t r i b u t e to the p l a n t s drought t o l e r a n c e . A l s o , a p p l i c a t i o n of t h i s growth retardant increases l e a f thickness i n c e r t a i n other p l a n t s which might a l s o c o n t r i b u t e to drought r e s i s t a n c e . The best success with i n c r e a s i n g e i t h e r drought r e s i s t a n c e or t o l e r a n c e has been demonstrated i n wheat, b a r l e y , grapes, beans, a p p l e s , sunflower, and g l a d i o l a s . Treatment with c e r t a i n growth r e t a r d a n t s a l s o increases a r e l a t e d p h y s i o l o g i c a l phenonomen, i . e . , s o l t t o l e r ance. The use of p l a n t growth r e t a r d a n t s to increase the t o l e r a n c e of p l a n t s to high concentrations of s a l t has been most s u c c e s s f u l with wheat, soybean and s p i n a c h . The use of i n h i b i t o r s or plant growth r e t a r d a n t s to i n c r e a s e r e s i s t a n c e to low temperatures has been most s u c c e s s f u l with cabbage, tomato, woody p l a n t s , a p p l e s , p e a r s , wheat, c i t r u s , r a s p b e r r y , grapes, mulberry, strawberry, and azalea.. A p p l i e d to c e r t a i n c r o p s , p l a n t growth r e g u l a t o r s can change the timing of crop development. Such developmental change might enable a crop to avoid the e f f e c t s of adverse environmental f a c t o r s , such as abnormally low temperatures or l a c k of water. I t a l s o might i n t e r f e r e w i t h the r a t e of p l a n t development, thereby d i s r u p t i n g the normal l i f e c y c l e of i n s e c t p e s t s . This, i n t u r n , may o f f e r a new method of i n s e c t c o n t r o l . The t e r m i n a t i o n of cotton f r u i t i n g by the use of chemicals i s a new approach f o r i n s e c t c o n t r o l . S e v e r a l p l a n t growth r e g u l a t o r s have been found which are e f f e c t i v e i n t h i s treatment. They are two types: 1) f a s t - a c t i n g and n o n - p e r s i s t e n t , and 2) s l o w - a c t i n g and p e r s i s t e n t . The slow a c t i n g p e r s i s t e n t growth r e g u l a t o r type i s represented by chlormequat (Cycocel or CCC) and c h l o r f l u r e n o l ( m e t h y l - 2 - c h l o r o - 9 - h y d r o x y - f l o u r e n e - 9 -



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carboxylate). The f a s t - a c t i n g type i n c l u d e s 2,4-D and 3,4d i c h l o r o i s o t h i a z o l e - 5 - c a r b o x y l i c a c i d . Mixtures of 2,4-D with e i t h e r of the two p e r s i s t e n t growth r e g u l a t o r s i s more e f f e c t i v e than 2,4-D a p p l i e d alone. A l l of these treatments have been t e s t e d e x t e n s i v e l y and found to be e f f e c t i v e . I t i s now f e l t that they are s u i t a b l e f o r use by entomologists i n l a r g e s c a l e t e s t i n g of chemical termination of f r u i t i n g i n cotton for i n s e c t control. Another area which might be considered of a p l a n t growth r e g u l a t o r y nature i s the use of "safening agents" with h e r b i c i d e s and other p e s t i c i d e s i n order to reduce the t o x i c e f f e c t s on crops under c o n d i t i o n s where i t i s necessary to use the p e s t i cides (20,21,22). Recent Japanese work shows that such p o l y amines as 1,8-diaminooctane or t h e i r s a l t s can be used as s a f e n ing agent f o r phenylcarbamoyl-amino a c i d h e r b i c i d e s . For example, the a p p l i c a t i o n of one of the a l a n i n e phenylcarbamoyl h e r b i c i d e s decreased the f i n a l y i e l d of wheat by 39% while the simultaneous a p p l i c a t i o n of a polyamine r e s u l t e d i n only a 4% decrease i n y i e l d (23). I n c r e a s i n g Crop Y i e l d s Corn An e x c i t i n g development has been the use of the h e r b i c i d e 2 , 4 - d i n i t r o - 6 - s e c - b u t y l p h e n o l (dinoseb) as a spray a p p l i e d to leaves at low concentrations to increase the y i e l d of c o r n . D r . A l v i n J * Ohlrogge of Purdue U n i v e r s i t y reported i n 1969 that only a few grams per acre of t h i s compound boosts the y i e l d of corn 5 to 10%. Since h i s f i n d i n g s were announced, however, i n v e s t i g a t o r s i n v a r i o u s p a r t s of the country have published c o n f l i c t i n g r e p o r t s on the e f f e c t i v e n e s s of the compounds, p o s s i b l y because of v a r i a t i o n s i n the genetic background of the d i f f e r e n t corn v a r i e t i e s used. N e v e r t h e l e s s , three companies (Dow Chemical, Helena Chemical, and Agway) are now marketing formulations of t h i s chemical f o r t h i s use. The most recent r e p o r t on dinoseb for i t s e f f e c t s on sweetcorn y i e l d s i n the midwest show p o s i t i v e e f f e c t s on three v a r i e t i e s but decreased y i e l d s w i t h a f o u r t h v a r i e t y (24). Soybeans In the I 9 6 0 s , 2 , 3 , 5 - t r i i o d o b e n z o i c a c i d was considered a s p e c t a c u l a r p l a n t growth r e g u l a t o r . When a p p l i e d to the leaves of soybeans, i t shortens the p l a n t s , increases t h e i r b r a n c h i n g , s t i f f e n s them, and increases pod set (thus i n c r e a s i n g y i e l d ) . U n f o r t u n a t e l y , the compound i s not always e f f e c t i v e . Scientists have found that the timing of i t s a p p l i c a t i o n i s very c r i t i c a l and that d i f f e r e n t v a r i e t i e s respond d i f f e r e n t l y . Hence, r e s u l t s are d i s a p p o i n t i n g l y i n c o n s i s t e n t , and the use of t h i s compound to i n c r e a s e soybean y i e l d s has been d i s c o n t i n u e d . 1



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Rubber. The use of 2 - c h l o r o e t h y l phosphonic a c i d (ethephon) to boost the y i e l d of l a t e x from rubber trees has become standard e s t a t e p r a c t i c e i n recent y e a r s . T h i s compound increases the flow of l a t e x and the y i e l d s of dry rubber from commercially important tree v a r i e t i e s as much as 100%. In a d d i t i o n , ethephon helps to preserve the bark, which normally i s cut r e g u l a r l y to permit the flow of l a t e x . As a r e s u l t , the economic l i f e of the t r e e i s prolonged. Ethephon breaks down i n t o ethylene, which i s probably the b a s i s f o r i t s a c t i v i t y . When 100% of the tapped t r e e s are t r e a t e d , the y i e l d i n c r e a s e varys from 36% to 130% depending on the time of y e a r . The highest y i e l d s are obtained from November through March. Starting i n A p r i l there i s a dip i n the y i e l d curve which reaches a low i n J u l y . At that time the curve s t a r t s going up, reaching the high l e v e l by November. The p r o f i t a b i l i t y i s even higher than the y i e l d r e t u r n . T h i s i s due p r i m a r i l y to the f a c t that a doubling of y i e l d was accomplished with no i n c r e a s e i n l a n d , number of t r e e s and t h e i r c u l t i v a t i o n , or work f o r c e . Guayule. Because i t can be grown i n the United S t a t e s , because i t can grow under extreme a r i d c o n d i t i o n s as i n desert areas good f o r l i t t l e e l s e at the present time, guayule has a t t r a c t e d i n c r e a s i n g i n t e r e s t since the o r i g i n a l work done on i t during World War I I . Rubber made from guayule i s equal i n every respect to that made from rubber t r e e s and commercially v a l u a b l e by-products are a l s o o b t a i n a b l e , i n c l u d i n g bagasse, r e s i n s , and l e a v e s . Two tons of bagasse and one ton of leaves can be obtained f o r each ton of rubber. Bagasse may be used i n paper pulp-making. The r e s i n s c o n t a i n v o l a t i l e and n o n v o l a t i l e t e r p e n o i d s , a high melting wax, a s h e l l a c - l i k e gum, d r y i n g o i l s , and s u c c i n i c a c i d . The leaves c o n t a i n a v a l u a b l e hard wax with a higher, melting point than that of high q u a l i t y cornuba. Recent reports from the USDA show that low cost t r i e t h y l a m i n e s , p a r t i c u l a r l y 2 - ( 3 , 4 - d i c h l o r o phenoxy t r i e t h y l a m i n e ) , sprayed about three weeks before harvest increased y i e l d s two to s i x times the normal 500 l b s . / a c r e . I n v e s t i g a t o r s c a r r y i n g out the work s t a t e that the compound works by causing the p l a n t s to express genetic t r a i t s more e f f i c i e n t l y — rubber producing c e l l s i n the p l a n t s become more a c t i v e and produce more rubber. Estimates are that the process of u s i n g such chemicals could i n c r e a s e o v e r a l l y i e l d s 30-35% and cut the growing time by 1-2 y e a r s . It i s important to note that e s t i mates suggest that a y i e l d of 1,000 l b s . / a c r e could support a rubber i n d u c t r y . Temperate F r u i t s . Among the most widely used plant growth r e g u l a t o r s i s s u c c i n i c a c i d - 2 , 2 - d i m e t h y l hydrazine (diaminozide), commonly r e f e r r e d to as A l a r or SADH. O r i g i n a l l y developed to reduce the


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v e g e t a t i v e growth of flower c r o p s , i t may have f a r greater value i n the f u t u r e as a r e g u l a t o r of f l o w e r i n g and f r u i t i n g . Treated with A l a r , t r e e s bear f r u i t a f t e r only four y e a r s , i n s t e a d of the usual seven to 10. Because i t i s a growth r e t a r d a n t , however, i t tends to dwarf the f r u i t t r e e s . A l a r promotes f r u i t s e t t i n g of grapes and a c c e l e r a t e s by s e v e r a l days the maturing of c h e r r i e s . I t a l s o i s used on apples, prunes, tomatoes, peanuts, and v a r i o u s ornamental c r o p s . On apple t r e e s , A l a r increases the firmness of the f r u i t and p r e vents i t from dropping permaturely. On tomato t r a n s p l a n t s , the compound r e t a r d s stem e l o n g a t i o n . Tropical Fruits. With the exception of 2,4-D and g i b b e r e l l i c a c i d treatments of a v a r i e t y of c i t r u s c r o p s , where improved f r u i t s e t , reduced f r u i t drop, and the a b i l i t y to delay h a r v e s t i n g without l o s s of f r u i t q u a l i t y are recognized b e n e f i t s , few a p p l i c a t i o n s have been developed f o r the use of hormone-type r e g u l a t o r s i n t r o p ical fruits. Recent work has shown that g i b b e r e l l i c a c i d w i l l delay postharvest r i p e n i n i n g and improve the q u a l i t y of bananas and that napthaleneacetic a c i d treatment of o i l palm to delay f r u i t a b s c i s s i o n has increased both y i e l d and o i l content. Sugarcane One of t h é most important developments i n recent years has been the use of chemicals as r i p e n e r s i n sugarcane. Work begun i n Hawaii i n the e a r l y I960 s has shown that a s u r p r i s i n g number of chemicals i n c r e a s e the sucrose content of cane at h a r v e s t . Some c a s u a l observers have suggested t h a t , because such a d i v e r s e a r r a y of chemical s t r u c t u r e s e f f e c t i v e l y r i p e n s sugarcane, "almost anything w i l l do so." A c t u a l l y , of course, t h i s i s not the case. Many thousands of compounds of a wide range of chemical types have been t e s t e d f o r t h i s e f f e c t , w i t h only a few dozen g i v i n g enough p o s i t i v e r e s u l t s to warrant s e r i o u s f u r t h e r study (25). The f i r s t m a t e r i a l s e r i o u s l y considered as a candidate r i p e n e r f o r i n c r e a s i n g sugar y i e l d s was the dimethylamine s a l t of 2 , 3 , 6 - t r i c h l o r o b e n z o i c a c i d . However, because of a number of t e c h n i c a l , environmental, and l e g a l proglems, t h i s m a t e r i a l did not prove s u c c e s s f u l commercially. N e v e r t h e l e s s , i t served as a standard f o r comparison i n screening t e s t s aimed at f i n d i n g b e t t e r sugarcane r i p e n e r s . C u r r e n t l y , only one product i s r e g i s t e r e d i n the U . S . f o r use as a sugarcane r i p e n e r . T h i s i s Ν , Ν - b i s (phosphonomethyl) g l y c i n e , known g e n e r i c a l l y as glyphosine and marketed by Monsanto as P o l a r i s . Although i t has been r e g i s t e r e d with the Environmental P r o t e c t i o n Agency f o r only about three y e a r s , i t already has been used to t r e a t s e v e r a l hundred thousand acres of sugarcane throughout the w o r l d . I t now i s used commercially i n Hawaii, Texas, F l o r i d a , Guyana, B r a z i l , Guatemala, Jamaica, 1


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and

Mauritius. The ethylene-producing compound ethephon i s used commerc i a l l y on sugarcane i n South A f r i c a n and Rhodesia. Both Cycocel and 7-oxabicyclo ( 2 , 2 , 2 , l ) h e p t a n e - 2 , 3 - d i c a r b o x y l i c a c i d (sold by Pennwalt as Ripenthol) have been r e g i s t e r e d f o r experimental use on sugarcane i n the U . S . and are under t e s t i n s e v e r a l other countries. Experimental r e g i s t r a t i o n i s expected i n the near future for evaluating N - 2 , 4 - d i m e t h y l - 5 - t r i f l u o r o m e t h y l ) - s u l f o n y l aminophenyl acetamide ( m e f l u i d i d e ) , i n the f i e l d as a sugarcane ripener. I t i s a v a i l a b l e from 3M as Embark, and s e v e r a l other companies have p o t e n t i a l products f o r t h i s use nearing t h i s stage (26). The f i n a n c i a l r e t u r n to the grower i s s t i l l s u b s t a n t i a l , d e s p i t e the low current p r i c e of sugar. The increased sugar y i e l d produced by such compounds v a r i e s from 10 to 20%, depending on the v a r i e t y of sugarcane t r e a t e d , as w e l l as p r e v a i l i n g weather and s o i l c o n d i t i o n s . F o r t u n a t e l y for the acceptance of chemical r i p e n i n g of sugarcane, the f i r s t such chemical ( P o l a r i s ) was introduced commercially i n 1974, when the p r i c e of sugar was high and the p o t e n t i a l r e t u r n to the grower was enormous. The chemically stimulated r i p e n i n g of sugarcane i s d e f i n i t e l y here to s t a y , even though the p r i c e of sugar has dropped to an e x t r e mely low l e v e l . D i s c u s s i o n and Remarks Compounds that r e g u l a t e crop m a t u r i t y are e s p e c i a l l y l i k e l y to have a dramatic impact on a g r i c u l t u r e i n the years ahead. In many i n s t a n c e s , these chemicals might not increase y i e l d s d i r e c t l y but might prevent l o s s e s caused by f a i l u r e to achieve maturity. The use of r i p e n i n g compounds i n sugarcane i s a good example. T h i s already has r e s u l t e d i n a 10 to 20% i n c r e a s e i n y i e l d s i n c e r t a i n parts of the world. Changes i n c u l t u r a l p r a c t i c e s to adjust the use of r i p e n e r s probably w i l l i n c r e a s e sugar y i e l d s even more. Chemical companies have c o n s i d e r a b l e i n t e r e s t i n the p l a n t growth r e g u l a t o r f i e l d , and they have great a b i l i t y f o r d i s covering and developing new growth r e g u l a t o r s . Their capacity s t a r t s with t h e i r c u r r e n t inventory of hundreds of thousands of organic compounds, many of which have never been tested as p l a n t growth r e g u l a t o r s . In a d d i t i o n , i t i s known that almost any b i o r e g u l a t e d process can be i n f l u e n c e d by organic chemicals. The s e c r e t i s to f i n d the chemical that has great enough t e c h n i c a l and commercial p o s s i b i l i t i e s . One of the l i m i t a t i o n s i s the l a c k of a s i n g l e , simple t e s t by which thousands of compounds can be evaluated. Such t e s t s are a v a i l a b l e f o r h e r b i c i d e s , but the f i e l d of p l a n t growth r e g u l a t i o n i s much more complex. For plant growth r e g u l a t i o n , the r a t e of a p p l i c a t i o n of the chemical and the stage of p l a n t growth are two v a r i a b l e s that must be considered almost from the beginning. A l s o , f o r many responses, i t i s necessary to grow


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a plant f o r i t s e n t i r e l i f e c y c l e , which i s an expensive, timeconsuming procedure. Major e f f o r t s are being made i n commercial and academic research centers to t a c k l e the d i f f i c u l t problem of how best to evaluate growth r e g u l a t i o n i n the i n i t i a l stages of experimentation.

Literature Cited


1.

Gowing, D. P., Leeper, R. W., "Induction of flowering in pineapple by beta-hydroxyethylhydrazine", Science (1955) 122,1267. 2. Burr, G. O., Hartt, C. E., Brodie, H. W., Tanimoto, T . , Kortschak, H. P., Takahashi, D., Ashton, F. Μ., Coleman, R. E. "The sugarcane plant", Ann. Rev. Plant Physiol. (1957) 8, 275. 3. Tanimoto, T . , Nickell, L. G., "Field control of sugarcane flowering in Hawaii with diquat", Proc. 12th Cong. ISSCT, Puerto Rico (1967) 113-116. 4. Wilson, W. C., "Four years of abscission studies on oranges", Proc. Fla. State Hort. Soc. (1969) 81,75. 5. Wilson, W. C., "Field testing of cycloheximide for abscission of oranges in the Indian River area", Proc. Fla. State Hort. Soc. (1971) 84,67. 6. Clark, R. K., E l l i s , H. T., "The use of Release, an abscis sion agent, to increase the productivity of pickers on processing oranges", Proc. Fla. State Hort. Soc. (1976) 89,72. 7. Ben-Tal, Y., Lavee, S., "Increasing the effectiveness of ethephon for olive harvesting", Hort. Science (1976) 11,489. 8. Cooper, W. C., Rasmussen, G. Κ., Rogers, B. J., Reece, D.C., Henry, W. Η., "Control of abscission in agricultural crops and its physiological basis", Plant Physiol. (1968) 43,1560. 9. Peacock, W. L., Jensen, F. L . , "Chlormequat doubles yield Malvasia bianca grapes", Calif. Agri. (1977) 31(6),9. 10. Dirou, J . F . , Logan, B. J., "Benefits from growth regulators on prune trees", Agri. Gaz. of NSW (1978) 89(1),47. 11. Dirou, J . F . , Logan, B. J., "Regulating prune maturity using chemicals", Agri. Gaz. of NSW (1977) 88(6),34 12. Tanimoto, T., Nickell, L. G., "Re-evaluation of gibberellin for field use in Hawaii", 1966 Rpts. Haw. Sugar Technol. (1967) 184-190. 13. Tanimoto, T., Nickell, L. G., "Effect of gibberellin on sugarcane growth and sucrose production", 1967 Rpts. Haw. Sugar Technol. (1968) 137-146. 14. Sowers, R., "Yield response of gibberellin at Waialua Sugar Company", 1976 Rpts. Haw. Sugar Technol. (1977) 274-277. 15. Wittwer, S. Η., "Growth regulants in agriculture", Outlook Agri. (1971) 6,205 of


10.

16. 17. 18.


19. 20. 21. 22. 23.

24. 25.

26.

NICKELL


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Cathey, H. M., Steffens, G. L., Stuart, N.W., Zimmerman, R. H.,"Chemicalpruning of plants", Science (1966) 153,1382. Larson, R. Α., "Stimulation of lateral branching of azaleas with dikegulac-sodium (Atrinal)", Jour. Hort. Sci. (1978) 53,57. Lierberman, Μ., "Post harvest responses and plant growth regulators",ACS Symp. Series No. 37 (Pesticide Chemistry in the 20th Century, J . R. Plimmer, ed.) (1977) 280-292. Vas'Kovskii, G.P., "Role of herbicides in the use of nutri ents by corn plants", Khim Sel'sk. Khoz. (1978) 16,58. [Russian]. Hoffman, O. L. "Chemical seed treatments as herbicide anti dotes", Weeds (1962) 10, 322. Hoffman, O. L., "Herbicide antidotes: concept to crop", Chemtech (1978) 8, 488. Leavitt, J . R. C., Penner, D., "Potential antidotes against acetanilide herbicide injury to corn (Zea mays)", Weed Res. (1978) 18, 281. Okii, M., Onitake, T., Kawai, M., Takematsu, T., Konnai, Μ., "Polyamine safening agents for phenylcarbomoylamine acid herbicides", Japan. Kokai Tokkyo Koho 78,94,035. January 24, 1977. Oplinger, E. S., "Response of sweet corn to foliar applica tions of dinoseb", Proc. 5th Ann. Mtg. Plant Growth Regulator Working Group (1978) 100-105. Nickell, L. G., "Chemical enhancement of sucrose accumula tion in sugarcane", ACS Advances in Chemistry Series No. 159 (Plant Growth Regulators, C.A. Stutte, ed.) (1977) 6-22. Nickell, L. G., "Chemical growth regulation in sugar cane", Outlook Agri. (1976) 9 (2), 57.

RECEIVED

June

19, 1979.


Plant Growth Substances - ACS Publications - American Chemical

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