Plant Bioregulators in Cereal Crops - American Chemical Society

4 Plant Bioregulators in Cereal Crops

Downloaded by UNIV OF AUCKLAND on May 3, 2015 | http://pubs.acs.org Publication Date: July 6, 1984 | doi: 10.1021/bk-1984-0257.ch004

A c t i o n a n d Use

JOHANNES JUNG BASF Aktiengesellschaft, Landwirtschaftliche Versuchsstation, D-6703 Limburgerhof, Federal Republic of Germany

Of the substances with bioregulatory action (PBRs) that have so far become known, only three have been used i n cereal crops to any s i g n i f i c a n t extent. However, partic u l a r l y i n European a g r i c u l t u r e , it has been possible to solve a big problem, namely the reduction of lodging in wheat, rye, barley and oats through treatment with growth retardants of the onium type (chlormequat chlor i d e , CCC; mepiquat c h l o r i d e , DPC) as well as the ethylene generator, ethephon. The successful a p p l i c a t i o n of these PBRs leads to the question of further possibilities of optimization induced by changes i n the phytohormone status of the various cereal species. There i s p a r t i c u l a r i n t e r e s t i n the favourable effect on the number of ear-bearing stems per area, the number of grains per ear, and the average grain weight. Further ways of optimizing production i n cereals using PBRs can be seen i n the increased stress tolerance and the improved utilization of water and plant nutrients v i a better root development. The s p e c i f i c development of PBRs relevant to practice presupposes not only further knowledge about phytohormone control mechanisms i n yield-determing factors and stress behaviour i n cereal plants but also sensible projection into the p a r t i c u l a r cereal cultivation system. In the discussion on the possibilities of using plant growth or bioregulators (PBRs) i n intensive cereal c u l t i v a t i o n , a picture i s frequently presented that might better fit into the period immediately preceding the turn of the millennium. On the other hand, we already have such highly e f f i c i e n t production models a v a i l a b l e for cereal c u l t i v a t i o n , and not only i n research 1aboratories and growth chambers. These have already been put into practice i n some of the areas worldwide under cereal c u l t i v a t i o n , which i s why they can be offered to other sectors of agriculture for a critical examination of t h e i r suitability under given c u l t i v a t i o n conditions. 0097-6156/84/0257-0029S06.00/0 © 1984 American Chemical Society

In Bioregulators; Ory, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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BIOREGULATORS: CHEMISTRY AND USES

The y i e l d p o t e n t i a l o f wheat i s s t a t e d by Aufhammer (1_) t o be about 22,500 kg/ha. Thus the g e n e t i c p o t e n t i a l o f t h i s most i m p o r t a n t c e r e a l i s by no means b e i n g f u l l y e x p l o i t e d , whereas t h i s e x p l o i t a t i o n i s o f c o u r s e o n l y f e a s i b l e w i t h a p p r o p r i a t e p r o d u c t i o n methods and a h i g h o u t l a y on o p e r a t i n g s u p p l i e s , the use o f which s o l e l y makes sense when t h e r e i s an adequate economic r e t u r n . The y i e l d components t h a t can be i n f l u e n c e d i n the c e r e a l p l a n t and the a c t i v e compounds t h a t a r e p r e s e n t l y a v a i l a b l e f o r t h i s a r e the s u b j e c t o f t h i s c o n t r i b u t i o n . The t o p i c s c o n c e r n i n g the uses t o which b i o r e g u l a t o r s have a l r e a d y been put and t h e i r p o t e n t i a l a p p l i c a t i o n s are o r i e n t e d m a i n l y t o c e r e a l growing i n C e n t r a l Europe.


Y i e l d s t r u c t u r e and y i e l d - d e t e r m i n i n g components i n c e r e a l s The g r a i n y i e l d o f an area r e s u l t s from the y i e l d o f each i n d i v i d u a l p l a n t . The l a t t e r y i e l d depends, i n i t s t u r n , on the s u c c e s s w i t h which the c e r e a l p l a n t passes through the v a r i o u s development s t a g e s . T a k i n g t h e s e development s t a g e s i n t o a c c o u n t , F i g u r e 1 shows the y i e l d components f o r the i n d i v i d u a l c e r e a l p l a n t and f o r the t o t a l plant population. P a r t i c u l a r importance a t t a c h e s t o : the number o f shoot per p l a n t and the d e n s i t y o f s h o o t s , the number o f e a r s and g r a i n s per p l a n t and a r e a , and the average g r a i n w e i g h t . A t t e n t i o n must a l s o be drawn t o a phenomenon t h a t has found p a r t i c u l a r i n t e r e s t i n c o n n e c t i o n w i t h the f o r m a t i o n o f y i e l d i n c r o p p h y s i o l o g y : t h i s i s the r e d u c t i o n o f the number o f s h o o t s , s p i k e l e t s and f l o r e t s t h a t form a t an e a r l y development s t a g e . I t i s c h a r a c t e r i s t i c f o r the development o f a c e r e a l p l a n t t h a t the number o f shoots approaches a maximum between emergence and the b e g i n n i n g o f stem e l o n g a t i o n t o drop a g a i n i n the r e d u c t i o n phase as the r e s u l t o f c o m p e t i t i o n and s t r e s s s i t u a t i o n s . The f o r m a t i o n o f e a r s w i t h the number o f f l o r e t s per e a r a l r e a d y determined i n the t i l l e r i n g phase i s , a f t e r q u i c k l y p a s s i n g through a maximum, a l s o s u b j e c t t o a r e d u c t i o n depending on the p a r t i c u l a r development c o n d i t i o n s . As the t h i r d i m p o r t a n t y i e l d component, the average g r a i n w e i g h t i s d e c i s i v e l y i n f l u e n c e d by the d e p o s i t i o n o f a s s i m i l a t e s d u r i n g the g r a i n f i l l i n g phase. P o s s i b i l i t i e s of i n f l u e n c i n g y i e l d formation with b i o r e g u l a t o r s cereal crops

in

I t i s s u f f i c i e n t l y w e l l known t h a t c u l t i v a t i o n measures ( i n p a r t i c u l a r sowing d e n s i t y ) , c r o p n u t r i t i o n measures ( e s p e c i a l l y the l e v e l o f n i t r o g e n f e r t i l i z a t i o n ) , and c r o p p r o t e c t i o n measures ( m a i n l y the e l i m i n a t i o n o f competing weeds and p h y t o p a t h o g e n i c f u n g i ) l e a d t o o p t i m i z a t i o n o f the y i e l d components mentioned and t o m a x i m i z a t i o n o f the o v e r a l l y i e l d . T h i s has i n c r e a s i n g l y r a i s e d the q u e s t i o n as t o what e x t e n t s u b s t a n c e s w i t h phytohormone o r a l s o m e t a b o l i c a c t i o n , which are grouped t o g e t h e r under the term p l a n t b i o r e g u l a t o r s , can be a d d i t i o n a l l y used f o r e x e r t i n g a p o s i t i v e i n f l u e n c e on the y i e l d of various cereal s p e c i e s .


4.

JUNG

Individual plant Seedling Downloaded by UNIV OF AUCKLAND on May 3, 2015 | http://pubs.acs.org Publication Date: July 6, 1984 | doi: 10.1021/bk-1984-0257.ch004

31

Plant Bioregulators in Cereal Crops

Number of shoots/ plant

Stages Emergence

. Tillering f Spikeiet formation

Total plant population Number of seedlings/ area

Density of shoots/ area

Reduction Ear-bearing stems/ area = grains initiated/area

Inflorescences/ plant grains initiated/plant

and Pollination ' Number of grains/ area

Number of grains/ plant Grain formation

ι

Single grain weight

Thousand grain weight

Grain yield/plant

Grain yield/area

I

F i g u r e 1. Y i e l d d e t e r m i n i n g components f o r the i n d i v i d u a l p l a n t and f o r the t o t a l p l a n t p o p u l a t i o n i n r e l a t i o n to d i f f e r e n t stages — t e r m s and survey.


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General c h a r a c t e r i z a t i o n of r e l e v a n t substances w i t h a e f f e c t in cereal species

bioregulatory

C l a s s i f i c a t i o n i n t o groups a c c o r d i n g t o p r i n c i p l e of a c t i o n . Of some 60 c o m m e r c i a l l y a v a i l a b l e substances w i t h a b i o r e g u l a t o r y e f f e c t a p a r t from the much l a r g e r number o f a c t i v e compounds d e s c r i b e d i n the l i t e r a t u r e s c a r c e l y more than t h r e e have so f a r a c t u a l l y been used i n p r a c t i c e i n c e r e a l growing (2J. To p r o v i d e an o v e r v i e w o f the most i m p o r t a n t substances t h a t have become known so f a r , a c l a s s i f i c a t i o n i n t o groups can be c a r r i e d out on the b a s i s o f the p r i n c i p l e of a c t i o n . In most cases the l a t t e r i s the i n t e n d e d i n f l u e n c i n g o f the p l a n t ' s hormone s t a t u s a c c o r d i n g t o the f o l l o w i n g p o s s i b i l i t i e s : s u p p l y o f a phytohormone p a r t i c i p a t i n g i n the e x i s t i n g e q u i l i b r i u m o r o f an analogous compound; - enhancing o r i n h i b i t i n g the hormone b i o s y n t h e s i s w i t h exogenous compounds ( p r e c u r s o r s o r s y n e r g i s t s , and a n t a g o n i s t s or i n h i b i t o r s ) ; v a r y i n g a v a i l a b i l i t y o f a phytohormone a t the s i t e o f a c t i o n by i n f l u e n c i n g i t s t r a n s p o r t and c a t a b o l i s m . On t h i s b a s i s , Table 1 l i s t s some o f the substances t h a t are r e l e v a n t to c e r e a l c r o p s , t o g e t h e r w i t h the phytohormones known so f a r c o n s i d e r i n g t h e i r r e l a t i o n i n terms o f a c t i o n o f the l a t t e r . At the p r e s e n t t i m e , the compounds i n t e r f e r i n g w i t h g i b b e r e l l i n b i o s y n t h e s i s (GA a n t a g o n i s t s ) and e t h y l e n e g e n e r a t o r s are worth o f s p e c i a l i n t e r e s t because they have a l r e a d y found e x t e n s i v e a p p l i c a t i o n i n some areas o f w o r l d c e r e a l c u l t i v a t i o n . In the case o f the o t h e r g r o u p s , i n t e r e s t i s c o n c e n t r a t e d on the q u e s t i o n o f t h e i r p o t e n t i a l use. Mechanisms and s p e c t r a of a c t i o n . An i n d i c a t i o n o f the mechanism o f a c t i o n o f the v a r i o u s b i o r e g u l a t o r s has a l r e a d y been g i v e n w i t h t h e i r c l a s s i f i c a t i o n i n Table 1 . However, the g i b b e r e l l i n a n t a g o n i s t s w i l l be d e a l t w i t h i n a l i t t l e more d e t a i l ; on the one hand, on account o f t h e i r importance i n p r a c t i c e , b u t , on the o t h e r hand, because we have been w o r k i n g on them f o r some t i m e . For GA a n t a g o n i s t s o f the onium t y p e , which i n c l u d e CCC ( c h l o r mequat c h l o r i d e ) and DPC (mepiquat c h l o r i d e ) as growth r e t a r d a n t s , i t i s assumed t h a t they i n h i b i t the c y c l i z a t i o n o f g e r a n y l g e r a n y l p y r o phosphate t o c o p a l y l pyrophosphate i n the c o u r s e o f GA b i o s y n t h e s i s ( s u r v e y see 3). A n c y m i d o l , t e t c y c l a c i s (NDA) and t r i a z o l e s i n h i b i t the s e q u e n t i a l o x i d a t i o n o f e n t - k a u r e n e t o e n t - k a u r e n o i c a c i d (4-, 5_, 6). These r e l a t i o n s h i p s are shown i n F i g u r e 2. I t must be s t a t e d i n c o n n e c t i o n w i t h the spectrum o f a c t i o n o f the GA a n t a g o n i s t s t h a t onium compounds have a d e c l i n i n g i n t e n s i t y o f a c t i o n from wheat, v i a r y e , b a r l e y , o a t s t o r i c e and m a i z e . T e t c y c l a c i s , however, a f t e r being taken up by the r o o t s , has an a p p r o x i m a t e l y comparable e f f e c t i n a l l c e r e a l s p e c i e s . An example of the e f f e c t on r i c e o f the v a r i o u s substances mentioned can be seen i n F i g u r e 3 . P a r t i c u l a r a t t e n t i o n s h o u l d be drawn t o the pronounced d i f f e r e n c e i n a c t i o n between the two groups o f c y c l i z a t i o n and o x i d a t i o n i n h i b i t o r s of GA b i o s y n t h e s i s .


JUNG



Table I . Overview o f r e l e v a n t substances w i t h a b i o r e g u l a t o r y e f f e c t i n c e r e a l s c l a s s i f i e d a c c o r d i n g t o t h e i r phytohormona1 interaction. Reference phytohormone

Compounds with homologuous or synergistic activity

Compounds with an antagonistic activity or inhibitors of biosynthesis

Auxins

Synthetic Auxins (NAA, Z4-D..)

Triiodobenzoic acid (TIBA)

Gibberellins Steroids Phthalimides StevioJ

Cytokinins

Benzyl- and Furfurylaminopurine Phenylurea derivatives

Abscisins

Terpenoic analogues of ABA Farnesol Jasmonic acid

Ethylene

Chloroethyl phosphonic acid (Ethephon) Aminocyclopropane carboxylic acid (ACC) (Auxins)

Onium compounds (CCC, CMH, DMC, DPC) Pyrimidine derivatives (Ancymidol) Norbornenodiazetine derivatives (NDA = Tetcyclacis) Triazoles

Aminoethoxivinyl glycine (AVG)



34 M V A - » - -IPP-

GPP-

. FPP—GGPP CPP

X

--'

ent-Kaurene J . ent-Kaurenoi \ _l _ ent-Kaurenal

Onium compounds (CCC, DPC)

Ancymidoi NDA (Tetcydacis) Triazoies


ent-Kaurenoic acid ent-7a-OH-Kaurenoic acid i GA Aldehyde ir

i n Gibberellins F i g u r e 2. I n t e r f e r e n c e of some growth r e t a r d a n t s w i t h g i b b e r e l l i n b i o s y n t h e s i s . ( A b b r e v i a t i o n s : MVA, m e v a l o n i c a c i d ; I P P , i s o p e n t e n y l pyrophosphate; GPP, t r a n s - g e r a n y 1 pyrophosphate; FPP, t r a n s f a r n e s y 1 pyrophosphate; GGPP, t r a n s - g e r a n y l g e r a n y l pyrophosphate; CPP, c o p a l y l pyrophosphate).

Ε θ

1ος concentration of active ingredient ( M )

F i g u r e 3. A c t i o n of v a r i o u s c o n c e n t r a t i o n s of growth r e t a r d a n t s (GA a n t a g o n i s t s ) on the growth of r i c e s e e d l i n g s . ΕΓΆ = CCC; φ - φ = DPC; Q-ty = t r i a z o l e 117 682; V ^ V = t r i a z o l e 130 827; #>-+'·== a n c y m i d o i ; Cr&O = t e t c y c l a c i s (NDA). KI^Q = c o n c e n t r a t i o n of a c t i v e i n g r e d i e n t by means of which a s h o r t e n i n g of 507 i s a c h i e v e d (see a l s o 1 1 ) . o


4. J U N G



A s p e c t s o f the use o f b i o r e g u l a t o r s stages o f c e r e a l s p e c i e s

i n the v a r i o u s

35

development

G e r m i n a t i o n and s e e d l i n g development. In t h e s e r i e s o f v a r i o u s d e velopment s t a g e s o f t h e c e r e a l p l a n t up t o t h e r e a l i z a t i o n o f g r a i n y i e l d , t h e q u e s t i o n o f i n f l u e n c i n g them a p p r o p r i a t e l y by t h e use o f b i o r e g u l a t o r s a l r e a d y a r i s e s a t t h e s t a g e o f g e r m i n a t i o n {]_). I t i s known t h a t g i b b e r e l l i n s s t i m u l a t e t h e g e r m i n a t i o n o f a l l c e r e a l s p e c i e s v i g o r o u s l y , which i s why, f o r example, GA3 i s used i n t h e p r o d u c t i o n o f m a l t . However, t h e r e have n o t up t o now been any s i g n i f i c a n t p o s s i b i l i t i e s o f a p p l i c a t i o n i n c e r e a l c r o p s f o r t h i s type o f r e g u l a t i o n . On t h e o t h e r hand, s u b s t a n c e s w i t h an o p p o s i t e a c t i o n t o g i b b e r e l l i n have met w i t h c o n s i d e r a b l y g r e a t e r i n t e r e s t both e x p e r i m e n t a l l y and i n p r a c t i c e . In t h i s c o n n e c t i o n a t t e n t i o n must be drawn, i n p a r t i c u l a r , t o t h e seed t r e a t m e n t o f w i n t e r wheat w i t h CCC, as i s p r a c t i s e d i n some r e g i o n s t o i n c r e a s e t h e w i n t e r r e s i s t a n c e o f wheat s e e d l i n g s . The improved o v e r w i n t e r i n g o f wheat t r e a t e d w i t h CCC was a l r e a d y shown by us i n model t r i a l s i n t h e m i d - s i x t i e s (8). The t r e a t ment o f both t h e seed and t h e s o i l w i t h CCC produced a c l e a r growth advantage f o r t h e t r e a t e d p l a n t s up t o the end o f t i l l e r i n g i n s p r i n g . Concerning t h e use o f CCC as a seed t r e a t m e n t , Zadoncev e t a l . (9) emphazise t h e l o w e r i n g o f t h e t i l l e r i n g node a f t e r seed t r e a t m e n t w i t h CCC as t h e reason f o r improved o v e r w i n t e r i n g . There i s apparent j u s t i f i c a t i o n f o r r e g a r d i n g t h e t r e a t m e n t o f seed w i t h b i o r e g u l a t o r s h a v i n g GA a n t a g o n i s t i c a c t i o n as a p o s s i b i l i t y f o r e x e r t i n g a s i g n i f i c a n t i n f l u e n c e on the development and s t r e s s p h y s i o l o g i c a l b e h a v i o u r o f c e r e a l p l a n t s . In p a r t i c u l a r , newer compounds such as t e t c y c l a c i s (_10, \l) can cause a change i n t h e s h o o t : r o o t r a t i o . A c c o r d i n g t o t h e model t r i a l s t h a t we have c a r r i e d o u t so f a r , t h e change i n t h e s h o o t : r o o t r a t i o can be a c h i e v e d u s i n g t h e s e substances n o t o n l y by a r e d u c t i o n o f both organ p a r t s v a r y i n g i n degree b u t a l s o by an a b s o l u t e promotion o f r o o t growth w i t h a s i m u l taneous r e d u c t i o n o f shoot l e n g t h . The example g i v e n i n F i g u r e 4 i l l u s t r a t e s t h i s e f f e c t . I t may be assumed t h a t t h e s e compounds can be used t o o p t i m i z e water and n u t r i e n t u t i l i z a t i o n and thus t o o p t i mize y i e l d i n c e r e a l c r o p s . Tillering. T i l l e r i n g assumes s p e c i a l importance w i t h i n t h e v e g e t a t i v e development o f a c e r e a l p l a n t . On t h e one hand, t h e number o f t i l l e r s developed determines t h e d e n s i t y o f t h e t o t a l crop t o a d e c i s i v e e x t e n t . On t h e o t h e r hand, even d u r i n g t h e t i l l e r i n g s t a g e , t h e d i f f e r e n t i a t i o n p r o c e s s e s f o r t h e f o r m a t i o n o f t h e g e n e r a t i v e organs b e g i n , t h i s f i x i n g , f o r example, t h e number o f s p i k e l e t s i n the i n d i v i d u a l e a r . What i s d e c i s i v e f o r t h e number o f e a r - b e a r i n g stems p e r area and f o r t h e number o f g r a i n s p e r e a r i s t h e q u a n t i t a t i v e r e s u l t o f t h e f o r m a t i o n o f these y i e l d components and o f t h e i r r e d u c t i o n d u r i n g t h e subsequent phase o f stem e l o n g a t i o n . I t i s known t h a t d a y l e n g t h , temperature and s u p p l y o f n u t r i e n t s have a s i g n i f i c a n t i n f l u e n c e on t h e c o u r s e o f these p r o c e s s e s . Less i n f o r m a t i o n i s a v a i l a b l e , however, about t h e phytohormone c o o r d i n a t i o n i n v o l v e d and t h e p o s s i b i l i t y o f u t i l i z i n g i t i n p r a c t i c e by u s ing appropriate a c t i v e substances. A p i c a l dominance, which i s determined p r i m a r i l y by t h e a u x i n l e v e l , but n o t s o l e l y by i t , no doubt has an i m p o r t a n t i n f l u e n c e on


36

BIOREGULATORS: C H E M I S T R Y A N D USES


t i l l e r i n g (12). T h e r e f o r e , the l a t t e r can be promoted by substances having an a u x i n - a n t a g o n i s t i c a c t i o n , such as t r i i o d o b e n z o i c a c i d (TIBA) ( Γ 3 , 1 4 ) . P l a n t b i o r e g u l a t o r s w i t h a G A - a n t a g o n i s t i c e f f e c t a l s o have a s t i m u l a t i n g i n f l u e n c e on t i l l e r i n g o r the number o f e a r b e a r i n g stems per a r e a , whereas g i b b e r e l l i n t r e a t m e n t reduces t h i s (15). G i b b e r e l l i n t r e a t m e n t tends t o hasten development, t o s h o r t e n the i n t e r v a l s between p a r t i c u l a r morphogenetic events and t o reduce the number o f organs l a i d down i n s u c c e s s i v e phases o f development, whereas r e t a r d a n t s g e n e r a l l y have the o p p o s i t e e f f e c t . S t a n d i n g a b i l i t y and l o d g i n g . A f t e r stem e l o n g a t i o n and heading the c e r e a l p l a n t reaches a v e r y c r i t i c a l phase f o r the f o r m a t i o n o f y i e l d , namely g r a i n f i l l i n g . The e f f e c t i v e and l o n g e s t p o s s i b l e f u n c t i o n i n g o f the a s s i m i l a t i n g organs i s e s s e n t i a l . The a s s i m i l a t e s r e q u i r e d f o r g r a i n f i l l i n g are produced d u r i n g a r e l a t i v e l y s h o r t p e r i o d . A c c o r d i n g t o Evans ( 1 6 J , o n l y 5 t o 10% o f the t o t a l a s s i m i l a t e s d e p o s i t e d i n the g r a i n o r i g i n a t e from the p r e - f l o w e r i n g p e r i o d . Any d i s t u r b a n c e i n the p h o t o s y n t h e t i c a c t i v i t y o f the a s s i m i l a t i n g p l a n t organs i n t h i s phase o f development - i n s u f f i c i e n t i n s o l a t i o n , l a c k o f w a t e r and n u t r i e n t s , l o d g i n g o r p a r a s i t i c a t t a c k - i s bound t o have an a d v e r s e e f f e c t on g r a i n f o r m a t i o n and y i e l d ( 1 7 ) . Lodging i s one o f the p r i n c i p a l problems i n i n t e n s i v e c e r e a l c u l t i v a t i o n t h a t has an u n f a v o u r a b l e e f f e c t , p a r t i c u l a r l y when i t o c c u r s i n the e a r l y r e p r o d u c t i v e s t a g e o f development. On the b a s i s o f fundamental i n v e s t i g a t i o n s c a r r i e d out by T o l b e r t ( 1 8 , 19_) on the a c t i o n o f v a r i o u s q u a t e r n a r y ammonium compounds on the growth o f wheat, i t was p o s s i b l e t o develop chlormequat (CCC) i n t o a v e r y e f f e c t i v e a n t i - l o d g i n g agent and t o i n t r o d u c e i t t o l a r g e areas o f wheat growing a l l o v e r the w o r l d ( 2 0 , 21). In West Germany, by f a r the g r e a t e s t p a r t o f a r e a under wheat c u l t i v a t i o n has been t r e a t e d w i t h CCC f o r many y e a r s now. H e r e , as i n a number o f o t h e r European c o u n t r i e s , t h i s p l a n t b i o r e g u l a t o r i s an i n t e g r a l element o f the wheat production system. As a g i b b e r e l l i n a n t a g o n i s t , CCC i n c r e a s e s the s t a n d i n g a b i l i t y o f wheat, on the one hand by r e d u c i n g the stem l e n g t h - e s p e c i a l l y i n the lower i n t e r n o d e s - a n d , on the o t h e r hand, by i n c r e a s i n g the s t e m ' s d i a m e t e r and by s t r e n g t h e n i n g i t s w a l l ( F i g u r e 5 ) . A l l the wheat v a r i e t i e s which have so f a r been t e s t e d r e a c t e d t o t h i s PBR, a l t h o u g h w i t h d i f f e r e n c e s i n d e g r e e . G e n e r a l l y the s h o r t straw v a r i e t i e s r e a c t more v i g o r o u s l y than the l o n g - s t r a w ones. In o r d e r t o a c h i e v e an optimum e f f e c t , the r a t e o f a p p l i c a t i o n must be a d j u s t e d t o the v a r i e t y a n d , i n a d d i t i o n , the growth s t a g e and the l o c a l c u l t i v a t i o n c o n d i t i o n s must be taken i n t o c o n s i d e r a t i o n . Only t h i s c a r e f u l h a r m o n i z a t i o n can e x p l o i t the p o s s i b i l i t i e s which t h i s growth r e g u l a t o r o f f e r s i n wheat growing f o r i n c r e a s i n g y i e l d , e s p e c a l l y on the b a s i s o f a h i g h e r s u p p l y o f n i t r o g e n . In o t h e r c e r e a l s p e c i e s - p a r t i c u l a r l y i n the v e r y l o d g i n g - s u s c e p t i b l e w i n t e r b a r l e y - the s t e m - s t a b i l i z i n g e f f e c t o f CCC i s c o n s i d e r a b l y weaker. A s e a r c h has t h e r e f o r e been c a r r i e d out f o r f u r t h e r s u b s t a n c e s . I t has emerged t h a t , i n a d d i t i o n t o CCC, a l a r g e number o f d i f f e r e n t compounds w i t h a charged c e n t r a l atom (onium compounds) a l s o have a b i o r e g u l a t o r y e f f e c t . Some o f the compounds of t h i s c l a s s o f s u b s t a n c e s are g i v e n i n F i g u r e 6 . However, i n s p i t e of an i n c r e a s e d



JUNG


F i g u r e 4. Example f o r the change o f the s h o o t : r o o t r a t i o a f t e r treatment of wheat w i t h t e t c y c l a c i s (NDA). L e f t : u n t r e a t e d ; r i g h t 15.0 mg a. i./100 kg seeds.

F i g u r e 5. E f f e c t s of i n c r e a s i n g CCC r a t e s (0.1-3 mg/pot) on the growth of wheat.


38

BIOREGULATORS: C H E M I S T R Y A N D USES


e f f e c t i n some cases compared w i t h CCC, the i n t e n s i t y o f stem s h o r t e n i n g and s t a b i l i z i n g i n w i n t e r b a r l e y i s not q u i t e a c h i e v e d . T h e r e f o r e , c o m b i n a t i o n s o f onium compounds w i t h the e t h y l e n e g e n e r a t o r ethephon were i n v e s t i g a t e d (22^ 23^, 2 4 ) . The two compounds complement each o t h e r . The e t h y l e n e g e n e r a t o r ensures p a r t i c u l a r l y t h a t stem s h o r t e n i n g c o n t i n u e s i n t o the g e n e r a t i v e p h a s e , s i n c e the c o n s i d e r a b l e r e d u c t i o n i n growth h e i g h t a c h i e v e d by the onium compounds i n the veget a t i v e stage i s o f t e n compensated l a t e r by the b a r l e y p l a n t t o a s u r p r i s i n g d e g r e e . Ethephon can be used as a s t a l k s t a b i l i z e r i n b a r l e y not o n l y i n c o m b i n a t i o n but a l s o on i t s own ( 2 5 ) . Ear and g r a i n development. The e a r s t r u c t u r e o f c e r e a l s , e s p e c i a l l y t h a t o f wheat, e x h i b i t s d i f f e r e n c e s due both t o v a r i e t y and d e v e l o p ment. In p a r t i c u l a r , the f a c t t h a t the number o f f e r t i l e f l o r e t s i n the d i f f e r e n t l y i n s e r t e d s p i k e l e t s i n the e a r can v a r y as can the w e i g h t o f the i n d i v i d u a l g r a i n s deserves s p e c i a l a t t e n t i o n w i t h r e f e r ence t o the f o r m a t i o n o f y i e l d . A c c o r d i n g t o Aufhammer and Bangerth ( 2 6 ) , the p r o p o r t i o n o f f l o r e t s t h a t form g r a i n s v a r i e s between 40 and 80% w i t h i n the e a r , the tendency d e c r e a s i n g upward and downward from the c e n t r a l r e g i o n ( F i g u r e 7 ) . At the base o f the e a r one t o f o u r s p i k e l e t s are o f t e n s t e r i l e . The w e i g h t o f the i n d i v i d u a l g r a i n s w i t h i n i n d i v i d u a l s p i k e l e t s may f l u c t u a t e between 30 and 60 mg. W i t h i n a s p i k e l e t , the b a s a l f l o r e t s g e n e r a l l y develop b i g g e r o r h e a v i e r g r a i n s than the d i s t a l ones. There i s much t o suggest t h a t these d i f f e r e n c e s i n e a r and g r a i n development a r e c o n t r o l l e d by phytohormones, a p p a r e n t l y a l o n g the l i n e s o f a dominance p r i n c i p l e . W i t h i n an i n f l o r e s c e n c e , the o l d e s t " d o m i nant" f l o r e t i n f l u e n c e s the development o f each subsequent one ( p r i m i g e n i a l dominance). I t i s t h e r e f o r e not s u r p r i s i n g t h a t GA a n t a g o n i s t s such as CCC and ancymidoi reduce the c o m p e t i t i v e a c t i o n o f v a r i o u s s i n k s and i m prove the synchrony o f e a r and g r a i n f o r m a t i o n ( 2 7 ) . B e s i d e s t h i s c o r r e l a t i v e i n f l u e n c e , attempts are b e i n g made t o promote g r a i n f o r m a t i o n by i n c r e a s i n g the s i n k c a p a c i t y . M i c h a e l and S e i l e r - K e l b i t s c h (28) have a l r e a d y e s t a b l i s h e d c o n n e c t i o n s between w e i g h t per g r a i n and the c y t o k i n i n c o n t e n t o f c e r e a l s . However, the exogenous s u p p l y o f c y t o k i n i n s i n the g r a i n f o r m a t i o n p h a s e , which has been i n v e s t i g a t e d by Herzog and G e i s l e r ( 2 9 ) , has so f a r shown o n l y l i m i t e d e f f e c t i v e n e s s , which may be l i n k e d t o the t r a n s p o r t b e h a v i o u r o f the phytohormone a p p l i e d . I t i s , however, p o s s i b l e t h a t compounds o f the c y t o k i n i n t y p e and o t h e r s u b s t a n c e s having a s e n e s c e n c e - r e t a r d i n g e f f e c t i n d i r e c t l y have a p o s i t i v e i n f l u e n c e on g r a i n f i l l i n g , i n t h a t they extend the f u n c t i o n i n g o f the p a r t s o f the p l a n t t h a t are m a i n l y a s s i m i l a t i n g i n t h i s phase ( 3 0 ) . On the o t h e r hand, any s p e c i f i c promotion o f the a s s i m i l a t i o n r a t e by o p t i m i z i n g the f i x a t i o n o f CO2, as has been f o r m u l a t e d by v a r i o u s a u t h o r s as the aim f o r C3 p l a n t s ( 3 1 , 3 2 , 3 3 ) , i s p r o b a b l y s t i l l f a r from r e a l i z a t i o n i n a c t u a l p r a c t i c e . B i o r e g u l a t o r s i n the c e r e a l c u l t i v a t i o n concept assessment

prospective

A p a r t from the p h y s i o l o g i c a l and t e c h n i c a l a s p e c t s , an i m p o r t a n t e c o nomic f a c t must be taken i n t o account i n the use o f b i o r e g u l a t o r s i n c e r e a l c r o p s , which i s a l r e a d y b e i n g p r a c t i s e d o r s h o u l d be s u b j e c t e d


JUNG


s

Ν

ν", _ cl

Cl-CH^CH -N-CH CH 2

N

3

/

Ρ

C H

3

S-CH / \ CH CH 3

3

Br"

• 3 Cl" Cl-CH -CH -N-NH

v * « ci c

C l 2

H

4

3

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DJS

CCC

w

CI-ryCH ^-C Hg

C H

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2

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CH

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3

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CH, cr

Plant Bioregulators in Cereal Crops - American Chemical Society

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