partial defoliation of vitis vinifera l. cv. cabernet sauvignon

8/13/2019 Partial Defoliation of Vitis Vinifera L. Cv. Cabernet Sauvignon

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P a r t i a l D e f o l i a t i o n o f V i t i s v i n i f e r a Lcv . C a b e r n e t S a u v i g n o n / 9 9 R i c h t e r :

E f f e c t o n R o o t G r o w t h C a n o p y E f fi c ie n c y ;G r a p e C o m p o s i t i o n a n d W in e Q u a l i t y

J . J . H U N T E R ~*, H . P. R U F F N E R 2, C . G . V O L S C H E N K 3, a n d D . J . L E R O U X 4

v i t i s v i n i f e r aL. cv. Cabernet Sauvignon/99 Richter was grown under f ield condi t ions . The effect of part ialdefol iat ion (33 ) in the low er half of the cano py at berry set s tage, and thereafter at pea-s ize and veraison,respect ively, on root development , d is t r ibut ion , and composi t ion as wel l as on canopy efficiency, y ield , grapecomp osi t ion , and wine qu al i ty was invest igated . Defol iat ion evident ly s t imulated occurre nce of f ine andextension roots , which ma y have increased the absorpt ive capaci ty of the root system. Root num ber decreasedwith increasing depth and roots occurred predominant ly in the top 800 mm of the so i l profi le . Starch was theprincipal carbohydrate s torage form in the roots , i rrespect ive of root s ize. Starch synthesis appeared notaffected by root age. Sucrose and organic acid pat terns were s imilar. Ci t r ic and tartaric acids were the mainorganic acids in roots , fo l lowed by malic acid . Elevated sugar and organic acid levels were found in roots oft reated v ines . The resul ts demon strate that the remaining leaves of part ial ly defol iated v ines were able to sustainnormal metabol ic funct ions in the roots . Canopy densi ty was efficient ly reduced by part ial defol iat ion , leadingto increased l ight penetrat ion , fru i t exposure, and photosynthet ic act iv i ty of mature and o ld leaves . Althoughpart ial ly defol iated v ines had much less leaf area per gram fresh berry mass at r ipeness , y ield increasedconsidera bly with defol iat ion at pea-s ize and veraison. R oot densi ty, y ield , and cane mass w ere related . Grapetotal so luble sugar content was unaffected , but t i t ratable acid i ty increased and the pH of the must decreasedwith part ial defol iat ion . Ostensib le increases in wine const i tuents (anthocyanins , phenol ics) , co lor densi ty,cul t ivar character in tensi ty, and overal l wine qual i ty were found in wines from treated v ines .

K E Y W O R D S : Vi t i s v i n i f e r a part ial defol iat ion , root growth, root composi t ion , canopy efficiency, grapecomposi t ion , wine qual i ty

Excess ive vege ta t ive g rowth and dense canop ies o fg rapev ines occur to some ex ten t i n a l l g r ape g rowingreg ions o f the w or ld . Th i s i s due p r im ar i ly to the use o fp r o p a g a t i o n m a t e r i a l f r e e o f h a r m f u l v i r u s e s a n d t h eind i sc r im ina te use o f f e r t i li ze r s , no tab ly n i t rogen , a swel l a s to improvement s in v i t i cu l tu r a l p r ac t i ces :e .g .so i l management , i r r iga t ion , cu l t iva t ion , and pes t andd i sease con t ro l. Long t e rm cho ices r egar d ing roo t s tock-sc ion combina t ions , t r a in ing a nd t r e l l i s ing sys t ems , andp lan t spac ing g rea t ly a f f ec t canopy dens i ty. I n Sou th

Af r i ca , a f avorab le c l imate , e spec ia l ly h igh t empera -tu r e , con t r ibu te to v igorous g rowth .Canopy microc l imate and source : s ink r e l a t ionsh ips

in g rapev ines a r e de t r imen ta l ly a f f ec t ed by excess ivegrowth , r e duc ing pho tosyn the t i c ac t iv ity o f l eaves (20 ,21 ,22,23,37,39,60,62) . Yield (59,63) , grape composi t ion,and wine q ua l i ty (7 ,16 ,17 ,61 ,64 ,65) a r e a l so nega t ive lyaf f ec t ed . High humid i ty and low a i r f low in a dense

1,3.4Plant Physiologist, P lant Phys iologist and Agricu ltural Research Tech nician, respe ctively,Nietvoorbij Inst i tu te for Vit iculture and Oenology, Private Bag X5026, 7599 Stel lenbosch,Repu blic of South Africa; 2Enzymologist, Institute of Plant Biology, Myc ology and Phytochem istry,Unive rsity of ZQrich, Zollikerstrasse 107 , CH- 8008 ZL~rich, Switzerland.

Corresponding author.

This research wa s conducted at the Nietvoorbij Inst i tu te for Vit iculture and Oenology.

Acknowledgements: Valuable echnical contributions by A. J . Heyns, E. Burger, W. J . Hendricks,L. M. Paulse, and R. Skrivan are appreciated.

Presented in part at the IV International Symposium on Grapevine Physiology, 11-15 Ma y 1992,Italy,and at the InternationalSymposium on Table G rape Production, 28-29 June 1994, California,USA.

Manuscrip t submitted for publicat ion 20 June 1994.

Copyright 1995 by the American Society for Enology and Vit iculture. All rights reserved.

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canopy- in t e r io r (24) p romote bunch ro t a s r epor t ed S m a r t e t a l . (64) . Excess fol iage fur ther impedes effet ive pes t and d i sease con t ro l ( 67) . Aga ins t t h i s bacground , excess ive v igor i s o f majo r concern to p roducs t r iv ing to ob ta in p ro longed max imum produc t ion qua l i ty g r apes .

I t is known th a t g r apev ine l ea f pho tosyn thes i s i n f luenced by var ious f ac to r s (22 and r e f e r ences thein ) and pho toass imi l a t e supp ly to the va r ious s incompr i ses a com plex sys t em of d ive r s ion and ba lan(20,21,37,39,52). Minim izing v egeta t ive domina nce wthere fo re , r equ i r e ca r e fu l p l an t man ipu la t ion to pven t phys io log ica l imba lances and ensure tha t bosources and sinks funct ion to ful l capaci ty.

Par t ia l defol ia t ion is widely recognized as an iva luab le p r ac t i ce to coun te r ac t t he de le t e r ious e f fec tsexcessive growth and plays a benef ic ia l ro le in grapv ine p roduc t ion (35 ,37 ,38 ,64) . How ever, i n man y expimen t s wi th pa r t i a l de fo l i a t ion , l eaves were ind i sc r iina t e ly r emoved and p lan t s severe ly s t r essed . Whfocus ing on a s ing le p rob lem, shor t - and long- t eeffects on leaf , f rui t , an d root physiology were f req uely neglected . The refore , th e effects of d i fferent de gre

of pa r t ia l defol ia tion (33 and 66 ) over the whocanopy, commencing a t d i f f e r en t deve lopmenta l s t agof the v ine (budb ur s t , b e r ry se t , pea -s i ze , and vera i soon var ious phys iolog ica l a spec t s were exam ined ex tesively (16,17,18,21,22,23,24,25) . Based on this s tudymethod to de fo l i a t e g r apev ines d i sc r imina t ive ly awi th pract ical appl icabi l i ty was suggested. The obj

A m . J . E n o l . V i t i c . , Vo h4 6 N o . 3 , 1 9 9 5


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PA RT I A L D E F O L I AT I O N 3 0 7

t i v e o f t h e p r e s e n t i n v e s t i g a t i o n w a s t o t e s t t h i s s e l e c t i v ed e f ol ia t io n m e t h o d b y m e a s u r i n g s o m e k e y p a r a m e t e r s ,i n c l u d i n g c a n o p y e f f i c i e n c y, y i e l d p a r a m e t e r s , m u s tc o m p o s it i o n, a n d w i n e q u a l i t y. E f f e c t s o n d e v e l o p m e n t ,d i s t r i b u t i o n , a n d c a r b o h y d r a t e a n d o rg a n i c a c i d c o n -t e n t s o f t h e r o o t s y s t e m a r e e m p h a s i z e d .

M a t e r i a l s a n d M e t h o d s

E x p e r i m e n t a l v i n e y a r d : A n l 1 -yea r-o ld v ine -y a r d , s i t u a t e d i n t h e We s t e r n C a p e a t N i e t v o o r b i j ,S t e l l e n b o s c h , w a s u s e d .Vi t i s v i n i f e r aL. cv. Caberne tS auv ignon ( c lone CS 46) , g r a f t ed on to 99 R ich te r ( c loneRY 30) , w a s s pace d 3 . 0 1 .5 m on a G le n ros a s o i l (S e r ie s1 3 , K a n o n k o p ) ( 4 3 ) a n d t r a i n e d t o a 1 . 5 - m s l a n t i n gt r e l l is d e s c r i b e d b y Z e e m a n ( 7 7 ). S h o o t s n o t s i t u a t e d o nt w o - b u d s p u r s w e r e s u c k e r e d a t a p p r o x i m a t e l y 3 0 - c ms hoo t l eng th .

S o i l c h a r a c t e r i s t i c s : The s o i l w as doub le deep -p l o u g h e d i n t w o d i r e c t i o n s t o a d e p t h o f 8 0 0 m m p r i o r t op l a n t i n g o f t h e v i n e s . C h e m i c a l c h a r a c t e r i s t i c s , c l ay,s il t, a n d s a n d c o n t e n t s i n t h e d i f f e r e n t so il la y e r s w e r er e p o r t e d b y H u n t e r a n d L e R o u x ( 18 ). B u l k d e n s i t y a n dw a t e r c o n t e n t i n f o u r s o i l l a y e r s ,i .e . 0cm to 30 cm, 30cm to 60 cm, 60 cm to 90 cm, and 90 cm to 120 cm w ered e t e r m i n e d d u r i n g t h e w i n t e r a c c o r d i ng to s t a n d a r dm e t h o d s . P h y l l o x e r a , m a rg a r o d e s , a n d n e m a t o d e o c c u r -r e n c e i n t h e s o i l w a s d e t e r m i n e d w i t h m e t h o d s d e -s c r ibed by D e K le rk (8 , 9 ) and Loubs e r (42 ) .

D e f o l i a t i o n t r e a t m e n t s : T h r e e t r e a t m e n t s w e r eapp l i ed : 0 (non-defo l i a t ed ) , and tw o r es pe c t ive 33d e f o l ia t i o n t r e a t m e n t s ( c o n s e c u t iv e r e m o v a l o f o n e o u to f e v e r y t h r e e l e a v e s ) a p p l i e d e v e n l y o n m a i n a n d l a t e r a ls hoo t s f rom s ide to s ide in the canopy. The f i r s t 33d e f o l ia t i o n on b o t h t h e s e t r e a t m e n t s w a s a p p l i e d i n t h ez o n e o p p os i t e a n d b e l o w b u n c h e s a t b e r r y s e t s t a g e . T h e

r e m a i n i n g p a r t o f t h e l o w e r h a l f o f t h e c a n o p y w a ss u b s e q u e n t l y 33 d e f o l i a te d a t e i t h e r p e a - s i z e ( t r e a t -m e n t t w o ) o r v e r a i s o n ( t r e a t m e n t t h r ee ) .

R o o t s t u d y . R o o t d i s tr i b u t i o n : To d e t e r m i n e r o o td i s t r i b u t io n , t h e p r o f il e w a l l m e t h o d o f B S h m ( 3) w a su s e d , a s m o d i f i e d b y H u n t e r a n d L e R o u x ( 1 8 ) . R o o t sw e re p lo t t ed in eac h o f six s o il dep th s (0 - 20 cm, 20 - 40cm, 40- 60 cm, 60- 80 cm, 80 - 100 cm, an d 100 - 120 cm)in f ive roo t d iamete r c l a s s es :i .e . < 0 .5 m m , 0 . 5 m m t o 2m m , 2 m m t o 5 m m , 5 m m t o 1 0 m m , a n d > 1 0 m m ( 66 ).Roo ts w ere ca tego r iz ed as f ine ( 1 0 m m ) r o o t s a c c o r d i n g to R i c h a r d s ( 54 ).

R o o t sa m p l i n g :Roots f rom each o f the above f ivec l a s s e s w e r e s a m p l e d r a n d o m l y i n t h e w h o l e p r o f i l e .

T h e y w e r e t h e n f r o ze n a t - 2 0 C p r i o r to f r e e z e - d ry i n gw i t h a C h r i s t f r e e z e - d r y i n g u n it . R o o t s a m p l e s w e r eg r o u n d u s i n g a C y c l o te c 1 0 9 3 S a m p l e M i ll a n d s t o r e d a tr o o m t e m p e r a t u r e .

E x t r a c t i o n a n d a n a l y s es o f su c r o se h e x o sesa n d o r g a n i c a c i ds: A m o d i fi e d m e t h o d o f R u f f n e re t al .( 57 ) w a s u s e d f o r e x t r a c ti o n : I g d r y m a t e r i a l f r o m e a c hr o o t c l as s w a s s u s p e n d e d i n 5 0 m L M e O H - C H C 1 3 - 0 .2 MH C O 2 H ( 1 2: 5: 3 v/ v) ( p H a p p r o x i m a t e l y 4 .2 ) a n d h o m o g -

e n i z e d fo r 4 5 s ec o n d s u s i n g a n U l t r a - Tu r r a x m a c e r ao p e r a t i n g a t 2 0 5 0 0 rp m . T h e h o m o g e n a t e w a s t r af e r r e d to a 0 . 45-~ tm f i l t e r (M i l l ipo re Co .) and ex t r a c tr e p e a t e d w i t h 2 2 5 m L 8 0 e t h a n o l . T h e f i l te r r e s i dw a s f r o z e n a t - 2 0 C , f r e e z e - d r i e d , a n d k e p t f o r s t aa n a l y s i s . F i l t r a t e s w e r e c o m b i n e d , d r i e d i n a r o te v a p o r a t o r a t 3 5 C a n d t h e r e s i d u e r e d i s s o l v e d i n 5 5 0 a q u e o u s a c e t o n it r i l e . T h e e x t r a c t w a s p a s s

t h r o u g h a c o l u m n w i t h i n t e r m e d i a t e b a s e a n i o n c h a n g e r e s i n ( B i o - R e x 5 , B i o - R a d L a b o r a t o r i e s ) a n d o rg a n i c a c i d s s u b s e q u e n t l y d e s o r b e d f r o m t h e r ew i t h 1 0 H 2 S O 4. B o t h n e u t r a l s u g a r a n d o rg a n i c af r a c t i o n s w e r e p a s s e d t h r o u g h S e p - p a k C ls c a r t r i d ga n d s t o r e d a t - 4 C p r i o r to a n a l y s e s b y H P L C , u s i n g e q u i p m e n t a n d c o n d i t i o n s d e s c r i b e d p r e v i o u s l y ( 2 6 )

E x t r a c t i o n a n d a n a l y si s o f s t a r c h : A 5 0 - m gs a m p l e o f t h e f r e e z e - d r i e d , i n s o l u b le r o o t m a t e r i a l wt r a n s f e r r e d to a n E p p e n d o r f v ia l. O n e m L 8 0 a q u e oa c e t o n e w a s a d d e d , f o ll o w e d b y v o r t e x i n g ( 1 0 s ec ) as o n i c a t i o n ( 10 m i n ). T h e s u s p e n s i o n w a s l e f t a t - 4 C s i x h o u r s , c e n t r i f u g e d ( 1 0 m i n ) a t f u l l s p e e d i n E p p e n d o r f ce n t r if u g e , a n d t h e s u p e r n a t a n t d e c a n tT h e r e s i d u e w a s t h e n t a k e n u p i n 1 m L e t h a n o l at r e a t e d a s a b o v e , e x c e p t t h a t t h e t i m e l a p s e b e t w es o n i c a t i o n a n d c e n t r i f u g a t i o n w a s o m i t t e d . A f t e r a dt i o n o f 1 m L H 2 0 , t h e s a m p l e w a s w a s h e d a g a i n , s e d i m e n t f r o z e n a t 2 0 C a n d f r e e z e - d r i e d o v e r n i gT h e l y o p h i li z e d m a t e r i a l w a s t a k e n u p i n 5 5 0 ~ tL Hfo l low ed by vo r tex ing (10 s ec ) and s on ica t ion (10 miw h e r e a f t e r i t w a s l e f t a t - 4 C f o r 6 0 m i n u t e s ac e n t r i f u g e d . I m m e d i a t e l y a f t e r c e n t r i f u g a t i o n ( 10 m ia 5 0 - ~ L a l i q u o t w a s r e m o v e d a s c o n t r ol .

S t a r c h w a s t h e n g e l a t in i z e d b y in c u b a t i n g t h e s ap l e in a b o il i n g w a t e r b a t h ( 5 m i n w i t h o p e n c a p s a n dmi n c los ed ). A f te r a l low ing th e m ate r i a l to cool , 500

o f a n e n z y m e m i x c o n t a i n i n g 5 U ( z - a m y l a s e ( S i g m a6 3 8 0 ) a n d 2 U a m y l o g l u c o s i d a s e ( S i g m a A - 7 2 5 5) i n M N a - a c e t a t e ( a c e t i c a c i d / N a - a c e t a t e ) b u f f e r ( p H 5w a s a d d e d , t h e m i x t u r e v o r t e x e d f o r 1 0 s e c o n d s ai n c u b a t e d a t 4 0 C w i t h c o n s t a n t s h a k i n g a t 3 5 r p m ,a l l ow h y d r o l y z a t i o n o f s t a r c h [ v ia l s w e r e r e m o v e d av o r t e x e d ( 1 0 s e c) e v e r y 3 0 m i n u t e s ] . A f t e r t h r e e h o ut h e s a m p l e s w e r e c e n t r i f u g e d ( 1 0 m i n ) a n d d i l u t( 1 :3 9 ) w i t h w a t e r.

G l u c o s e g e n e r a t e d f r o m s t a r c h w a s d e t e r m i n e d u s i n g t h e A B T S [ 2, 2' a z i n o - di ( 3 e t h y l b e n z t h i a z o l i n e ) -s u l f o n a t e ] r e a g e n t , w h i c h c o n s i s t e d o f 3 . 45 g N a 2 H P O2H 20 , 1 . 6 g N aH 2 P O 4 H 20 , 2350 U g lucos e ox id( B o e h r i n g e r n o . 64 6 4 2 3 ), 3 7 5 U p e r o x i d a s e ( B o e h r i nno . 127361) and 125 mg A BTS (B oehr inger no . 10294d i s s o lv e d i n 2 5 0 m L H 2 0 .

A 50-~tL a l iquo t o f the d i lu ted s am ple w as m ixWi th 9 5 0 ~ tL o f t h e a b o v e r e a g e n t . A b s o r b a n c y w a s r ea t 4 3 6 n m a f t e r 3 0 m i n u t e s . T h e b l a n k c o n s i s t e d om i x t u r e o f w a t e r a n d r e a g e n t . To o b t a i n a g lu c os t a n d a r d c u r v e , s ev e n s t a n d a r d s w e r e p r e p a r e d :i .e . O5 , 10, 20, 30 , 40 , and 50 mg g lucos e /100 mL. R es u l t s e x p r e s s e d i n m g s t a r c h a f t e r m u l t i p l i c a t i o n w i t h a f a co f 0 .9 , w h i c h a l l o w s f o r t h e r e d u c e d m o l e c u l a r w e i g hg l u c o se i n t h e p o l y m e r.

A m . J . E n o l . Vit i c . Vo l . 4 6 N o . 3 1 9 9 5


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3 8 m H U N T E R e t a l

C a n o p y m e a s u r e m e n t s : T h e p o t e n t i a l o f v i n e s t op r o d u c e q u a l i t y w i n e g r a p e s w a s a s s e s s e d b y s c o r i n gc a n o p ie s w i t h t h e v i n e y a r d s c or e c a r d o u t l in e d b y S m a r te t a l ( 64 ). L i g h t i n t e n s i t y j u s t a b o v e t h e v i n e c o r d o n w a sd e t e r m i n e d i n t h e l a t e m o r n i n g w i t h a L I - C O R L i n eQ u a n t u m S e n s o r a n d e x p r e s s e d a s a p e r c e n t a g e o fa m b i e n t l i g h t i n t e n s i t y. P h o t o s y n t h e t i c a c t i v i t y ( m gC O z / dm 2 /h r ) o f b a s a l ( j u s t a b o v e b u n c h e s ) a n d m i d d l e

l e a v e s w a s m e a s u r e d w i t h a p o r ta b l e p h o t o s y n t h e s i sm e t e r ( A D C ) , a s d e s c r i b e d b y H u n t e r a n d Vi s s e r ( 2 2 ) .

Ve g e t a t i v e g r o w t h y i e l d a n d g r a p e c o m p o s i -t i o n : B u d d i n g , b u d f e r t il i ty, y i e l d , l e a f a r e a / g f r e s hb e r r y m a s s , c a n e m a s s , t o t a l s o l u b l e s o l i d s , t i t r a t a b l ea c i d i t y, a n d m u s t p H w e r e d e t e r m i n e d a s d e s c r i b e dprev ious ly (16 , 24 , 25 ) .

W i n e c o m p o s i t i o n a n d q u a l it y : Wi n e s w e r e m a d ea s r e p o r t e d b y H u n t e re t a l ( 17 ). A n t h o c y a n i n c o n t e n t ,c o lo r d e n s i t y a n d p h e n o l i c c o n t e n t o f w i n e s w e r e m e a -s u r e d s p e c t r o p h o t o m e t r i c a l l y a t 5 3 0 n m , 5 3 0 + 4 2 0 n m ,a n d 2 8 0 n m , r e s p e c t i v e l y, i n a Va r i a n U V / V I S s p e c t r o -p h o t o m e t e r ( M o d e l 2 2 0 0 ) u s i n g 1 0 m m q u a r t z c e l l s .Wi n e s w e r e e v a l u a t e d s e n s o r ia l l y f or c u l t iv a r c h a r a c t e ri n t e n s i t y a n d o v e r a l l w i n e q u a l i t y.

E x p e r i m e n t a l d e s i g n a n d s t a t i s t i c a l a n a l y se s :T h e e x p e r i m e n t w a s l a i d o u t a s a c o m p l e t e l y r a n d o m -i z e d d e s i g n . F o r t h e r o o t s t u d y, f i v e u n i f o r m , h e a l t h yv i n e s ( r e p l i c a t i o n s ) p e r t r e a t m e n t w e r e r a n d o m l y s e -l e c t e d . T h e s t u d y w a s c o n d u c t e d i n t h e f o u r t h g r o w t hs e a s o n a f t e r p a r t i a l d e f o l i a t i o n w a s c o m m e n c e d . D a t aw e r e c o l l e c t e d i n w i n t e r ( J u l y / A u g u s t ) .

C a n o p y, g r o w t h , y i e ld , a n d g r a p e c o m p o s i t io n m e a -s u r e m e n t s w e r e m a d e o n 1 4 r e p l i c a t i o n s ( o n e v i n e p l o ts )f o r e a c h o f t h e t h r e e t r e a t m e n t s . C a n o p y s c o r e s o f e a c ht r e a t m e n t w e r e d o n e o n f i v e v i n e s b y t h r e e j u d g e s .Tr e a t m e n t s w e r e a p p l ie d f o r t h r e e c o n s e cu t iv e y e a r s .D a t a w e r e c o l l e c t e d a t r i p e n e s s . E x c e p t f o r c a n o p ys c o re s , m e a n s o b t a i n e d o v e r t h e l a s t t w o y e a r s a r ep r e s e n t e d .

Wi n e q u a l i ty d e t e r m i n a t i o n s a n d e v a l u a t i o n s w e r em a d e o n d u p li c a t e w i n e s a f t e r t h r e e y e a r s . Wi n e s w e r ee v a l u a t e d s e n s o r i a l l y f or c u l t i v a r c h a r a c t e r i n t e n s i t y b y1 7 j u d g e s a n d f o r o v e ra l l w i n e q u a l i t y b y 2 2 ju d g e s ,u s i n g a n i n e - p o i n t s c a le . T h e s c o r e s o f e a c h j u d g e w e r ee x p r e s s e d a s a p e r c e n t a g e o f m a x i m u m s c or e . T h en a t u r e o f t h e d a t a w a s s u c h t h a t i t co u l d n o t b e s t a ti s -t i c a ll y a n a l y z e d .

W h e r e p o s s i b le , a o n e - w a y a n a l y s i s o f v a r i a n c e w a sp e r f o r m e d o n t h e r a w d a t a ; d i f fe r e n ce s b e t w e e n t r e a t -m e n t m e a n s w e r e d e t e r m i n e d u s i n g S t u d e n t s t - L S Dtes t .

R e s u l t s a n d i s c u s s i o n

S o i l c h a r a c t e r i s t i c s : A s r e p o r t e d e a r l i e r ( 18 ), c l a ya n d s i l t c o n t e n t o f t h e s o il g e n e r a l l y i n c r e a s e d w i t hd e p t h , w h i l e t h e p e r c e n t a g e o f s a n d i n t h e d i f f e r e n t s a n dc l a s s e s d e c r e a s e d . R e s i s t a n c e a n d p H o f t h e s oi l a s w e l la s P, K , a n d C a c o n t e n t d e c r e a s e d w i t h i n c r e a s i n gd e p t h , w h i l e M g c o n t e n t i n c r e a s e d . P e r c e n t a g e s o i lw a t e r i n c r e a s e d w i t h d e p t h , w h e r e a s t h e s o i l c o m p a c -

3 0 -

2 5 -

o~2 0

t _

9

1 5

n 1 00

5

- 2.0

1 . 5

1 . 0 =9o

0 . 5 mi

0 I , , 0 . 00 - 3 0 3 0 - 6 0 6 0 -9 0 9 0 - 1 2 0

S o i l l a y e r ( c m )

Fig. 1 . Soi l water content and bulk densi ty of a Glenrosa soi l (Ser ieKanonkop) a t Nie tvoo rb i j , S t e l l enbosch , m easu red in win te r.

t i o n i n d e x ( b u l k d e n s i t y ) w a s h i g h e r i n t h e t o p 6 0 cexcee d ing the c r i t i ca l va lue o f 1. 5 g /cm 3 o r roo t pene tt ion r epo r ted by R ichards (54 ) (F ig . 1 ) . G row th cont i o n s w i t h r e s p e c t t o s o i l w a t e r a n d b u l k d e n s i t y ws i m i l a r f o r n o n - d e f o l ia t e d a n d p a r t i a l l y d e f o l i a t e d v i( d a t a n o t s h o w n ) . T h e n u m b e r s o f n e m a t o d e s p e c ie s ap h y l l o x e r a w e r e i n s i g n i f i c a n t r e g a r d i n g g r a p e v ih e a l t h ( d a t a n o t s h o w n ) . M a rg a r o d e s w e r e n o t f o u n

R o o t d i s t r i b u t i o n : Roo t dens i ty w as no t s ign i fc a n t l y a f f e c t e d b y p a r t i a l d e f o l ia t i o n a s a p p l i e d i n ts t u d y. H o w e v e r, a n a p p a r e n t s t i m u l a t i o n o f r o o t d e n s( n u m b e r / m 2) w a s e v i d e n t a f t e r p a r t i a l l y d e f o l i a t i n g v ia t pea - s ize [397] and ve ra i s on [409] , r e s pec t ive ly, copared to non-defo l i a t ed v ines [383] . Th i s , a s w e l l a s o s t e n s i b l e i n c r e a s e i n r o o t d e n s i t y t h e l a t e r d e f o l i a tw as app l i ed , co r r es pond to p rev ious f ind ings on f i eg r o w n C a b e r n e t S a u v i g n o n ( 1 8) , b u t d o n o t s u p p o r t d e c r e a s e i n r o o t d r y m a s s f o u n d w h e n l e a f a r e a o f p

g r o w n M u s c a t d A l e x a n d r ie a n d T h o m p s o n S e e d lw a s r e d u c e d ( 5 , 3 3 ) . H o w e v e r, i t m u s t b e e m p h a s i zt h a t v i n e s u s e d i n t h e l a t t e r s t u d i e s w e r e o n l y o n e yo ld a n d l e a f a r e a s e v e r e l y re d u c e d , w h e r e a s v i n e s ui n t h e p r e s e n t s t u d y w e r e o l d e r t h a n 1 0 y e a r s a t t h e t id e f o l ia t i o n c o m m e n c e d .

F ine roo t s (


4/9

PA RT I A L D E F O L I AT I O N - - 3 0 9

Tab le 1 . Effec t o f 3 3 d e fo l ia t io n o f g rap ev in e so n th e to ta l n u mb e r o f ro o t s p e r d iame te r c la s s .

R o o t d i a m e t e r c la s s ( m m )

T r e a t m e n t 10

Contro l 631 62 29 11 1*Pea s ize defo lia t ion 659 77 16 9 1

*Veraison defolia t ion 674 78 23 8 2

Mean 6 5 5 a 7 2 b 2 3 b c 9 b c 1 c

* Defo l ia t io n in th e lo wer h a l f o f th e can o p y ; p reced ed b y d e fo l ia t io n in th eb u n ch zo n e a t b e r ry se t . Va lu e s d e s ig n a ted b y th e sam e le t t e r d o n o t d iff e rs ig n i f ic an t ly (p < 0 .0 5 ) .

b l an c / 99 R i c h t e r h a d a b e t t e r r e g e n e r a t i v e a b i l i ty t h a nt h i n n e r r o ot s, r e g e n e r a t i o n w a s c l e a rl y n o t im p e d e d b yd e f o li a ti o n . I t w o u l d e v e n s e e m a s i f t h e r o o t s y s t e ma d j u s t e d i t s g r o w t h r a t e b y i n i t i a t i n g n e w r o o t s , a s w a sfound fo r app le t r ees (44 ) .

R e g a r d l e s s o f t r e a t m e n t , t h e n u m b e r o f r o o ts d e -c reas ed w i th inc reas ing dep th ( c f . a l s o 51 ) (Tab le 2 ) . A si s g e n e r a l l y f o u n d f o r g r a p e v i n e s ( 1 8, 6 8, 7 1) , r o o t s w e r ep r e d o m i n a n t l y l o c a t e d i n t h e t o p 8 0 c m , b e y o n d w h i c h

t h e i r n u m b e r s d e c r e a s e d b y a f a c t o r of f o u r in t h e 1 0 0to 120 cm soi l layer.

I n t e r e s t i n g l y, r o o t o c c u r r e n c e ( Ta b l e 2 ) d e c r e a sw i t h d e c r e a s e i n s o il c o m p a c t i o n ( F i g . 1 ), in d i c a t i n g t hs o i l c o m p a c t i o n w a s n o t r e s t r i c t i n g r o o t p e n e t r a t i o nt h i s s t u d y (c f. a l so 5 0 ). T h e s l i g h t l y h i g h e r r o o t n u m bof pa r t i a l ly de fo l i a t ed v in es in the 40 cm to 120 cm l a y e r s u g g e s t a n i m p r o v e d p e n e t r a t i o n a n d u t i li z a t io f d e e p e r s o il l a y e r s , w h i c h m a y h a v e p o s i ti v e i m p l it io n s r e g a r d i n g p e r f o r m a n c e u n d e r n o n - i r r i g a t e d ao r d r o u g h t c o n d i ti o n s . I t w a s a l s o f o u n d b y H u n t e r aVi s s e r ( 2 2) t h a t , a l t h o u g h t h e r a t e o f p h o t o s y n t h ei n c r e a s e d w h e n v i n e s w e r e p a r t i a l l y d e f o l ia t e d , a l o wt r a n s p i r a t i o n : p h o t o s y n t h e s i s r a t io w a s n e e d e d b y t hleaves .

R o o t c o m p o s i t i o n : S t a r c h , s u g a r, a n d o rg a n ia c i d c o n c e n t r a t i o n s c o r r e s p o n d t o d a t a o f Wi n k l e r aWi l l i a m s ( 7 5 ), i n d i c a t i n g t h a t s t a r c h i s th e m a i n a s s ii l a t e s t o r a g e f o r m in t h e r o ot s , e x c e e d i n g 2 5 o f r o o t w e i g h t a n d r e p r e s e n t i n g 90 o f t h e c a r b o h y d r a ta n a l y z e d , f o ll o w e d b y s u c r o s e a n d a l m o s t i d e n t i c a l g

cos e and f ruc tos e concen t r a t ions (F ig . 2 and 3 ) . Rc l a s s e s d i f f e r e d i n t h e i r a b i l i t y t o f u n c t i o n a s s t a rs t or e s , p e r m a n e n t r o o ts h a v i n g t h e h i g h e s t c o n c e n t

Tab le 2 . Effect of 33 defolia t ion of grap evine s on the to ta l num ber of roots per so i l layer.

S o i l l a y e r ( c m )

T r e a t m e n t 0 - 2 0 2 0 - 4 0 4 0 - 6 0 6 0 - 8 0 8 0 - 1 0 0 1 0 0 - 1 2 0

Contro l 177 151 145 144 78 40

* Pea s iz e d e fo l ia tio n 1 6 8 1 3 9 1 6 4 1 5 7 8 9 4 4*Ve ra ison defolia t ion 177 151 156 153 106 43

Mea n 174 a 147 b 155 ab 151 b 91 c 42 d

* De fo l ia t io n in th e lo wer h a l f o f th e can o p y ; p reced ed b y d e fo l ia tio n in th e b u n ch zo n e a t b e r ry se t .Va lu e s d e s ig n a ted b y th e same le t te r d o n o t d i ff e r s ig n i fi c an t ly (p < 0 .0 5 ).

3 3 0 - - 2 0

3 0 0 -

2 7 0 -

A

m

- 1 5 E

o )

E1 0 ~

w

o. x

5 ~L . _

o

~

BB S t a r c h

S u c r o s eb

G l u c o s e a

a

N

ri.N

~N

< 0 . 5 0 . 5 2

a_~

2 - 5

ab

c ab

ab

bc

5 - 1 0 > 1 0

A 2 4 0 -

E 2 1 0 -

~ ' 1 8 0 -ID

~ 1 5 0 -

E 1 2 0 -J~o- 9 0 -m

6 0 -

3 0 -

0 0

R o o t d ia m e t e r c l a s s ( m m )

Fig . 2 . Su g a r co n ten t o f ro o t s o f d i ff e ren t d iame te r s i z e s . Va lu e s d e s ig n a ted b y th e same le t te r d onot d iffer s ignif icantly (p < 0 .05) for ea ch sug ar.

t i o n . T h e r e s u l t s n e v e r t h e l e s s i n dc a t e t h a t t h e a c t i v i t y of s t a r c h - s yt h e s i z i n g e n z y m e s w a s n o t l i m i t e d roo t age . S ince no ev iden t conver s io f s t a r c h t o s u g a r d u r i n g t h e w i n td o r m a n c y p e r i o d w a s f o u n d ( 7 5 ) , iv e r t a s e - m e d i a t e d h y d r o l y si s o f sc r o se p r o b a b l y c o n t i n u e s t o c a t e r fm a i n t e n a n c e m e t a b o l i s m ( r e s p i r a try lo s s es ) , a lbe i t a t a low ra te . I nvet a s e i s k n o w n t o b e a b u n d a n t i n g r a p

v ines (57 ) . Th i s , how ever, r a i s es tq u e s t i o n o f t h e c a r b o n s o u r c e w h i c ha b l e to s u s t a i n a c c u m u l a t i o n o f sc r o s e a l o n g a c o n c e n t r a t i o n g r a d i ei n t h e r o o ts . G i v e n t h e h i g h e r r e l a t ih e x o s e c o n c e n t r a t i o n s o f f i ne , e x t es io n , a n d p e r m a n e n t r o o t s, t h e y s e et o be p l a y i n g a d u a l r o l e i n a s s i m i l am e t a b o l i s m , n a m e l y u t i l i z i n g s u ga n d s t o r i n g s t a r c h , w h e r e a s t h e f r a mw o r k r o o t s t e n d e d t o be m o r e s t o r a go r i e n t a t e d .

S u c r o s e a n d o rg a n i c a c i d l e ve l s t h e d i f f e r e n t r oo t c l a s se s b e h a v e d s i mi l a r l y. A s w a s f o u n d b y K l i e w(28 , 29 ) , t a r t a r i c and c i t r i c ac ids w ep r e d o m i n a n t , w i t h m a l i c a ci d p r e s ei n s m a l l e r a m o u n t s . A r e v e r s e p at e r n w a s f o u n d i n x y l e m e x u d a t e s o n e - y e a r -o l d s p u r s o f C h a r d o n n a y j ub e f o r e b u d b u r s t ( 11 ) . T h e i n t e r m e da tes o f the t r i ca rboxy l ic ac id cycc i t r i c and mal ic ac id , may be u t i l i za s a n a p l e r o t i c s o u r c e s o f e n e r g( 3 4 , 5 3 , 5 6 ) i n m a i n t e n a n c e r e a c t i o n

Am. J . En o l . Vi t i c . , Vo l .4 6 , N o . 3 , 1 9 9 5


5/9

3 1 0 - H U N T E R e t a

3 tB B T a r t a r i c a c i d

~'w 2 .5 - I - - ]C i t r i c a c i d i

t- ~ M a l i c a c i dp , ~ ab

2 . 0o

~ 1.5 a b ao abg b b abm

.2 1 .0 bc ie-raO)

o 0 .5

0 , 0 < 0 . 5 0 . 5 - 2 2 - 5 5 - 1 0R o o t d i a m e t e r c l a ss m m )

F i g 3 O rg a n i c a c i d c o n t e n t o f r o o t s o f d i f fe r e nt d i a m e t e r s i z e s Va l u e s d e s i g n a t e d b y t h esam e let ter do not differ significantly (p < 0.05) for each o rgan ic acid.

a b

> 1 0

AWWmE

o

EJ OL_

or)

3 0 0 - a - 1 5a a B B C o n t r o l 1

[ ~ * P e a s i z e d e f o l i a t i o n* Ve r a i s o n d e f o l i a t i o n

-/ a

0 ~ ~ ~ ~ ~ ~ ~ ~ P ~ 0S t a r c h S u c r o s e G l u c o s e F r u c t o s e

{4W

1=

1 0 ~o

EID

X

o

Fig. 4. Effect of 33% defoliat ion of the grap evine on root starch and su gar content . *De foliat ionin the low er ha l f o f the canopy; preced ed by defo l ia t ion in the bunch zo ne a t ber ry se t. Valuesdes igna ted by the sam e le t te r do no t d i ffe r s ign i fican t ly (p< 0 .05) for each sug ar or for s ta rch .

reser ves (5,6,24,25,30,32,33,45,49), where-as little negative or even beneficial effectsare observed when partial defoliation isapplied after veraison (24,25,46,58). Theresults on root distribution and composi-tion in the present study clearly demon-strate tha t neit her assimilate sources, norsize and activity of the root system were

depleted/affected by partial defoliation.Root systems of established, field-grownvines, therefore, do have the capacity towithstand the assumed stress conditionsinduced by partial defoliation. Photosyn-thates supplied by the remaining leaf areaduring the growth season were apparentlystill meeting/exceeding the demand forassimi lates needed for growth, storage andrespiration, processes which are criticallyimpor tant for survival of perennial plantsand sustained productivity (41). Althoughthe levels of root reserves do not fluctua tesubstantia lly durin g the dormancy period

(27,29,75), the data do not indicate whet h-er higher proportions of carbohydrateswere mobilized from storage regions tosupport growth in spring upon partial de-foliation in the previous season; if so, it wasnot detri mental . I t is possible th at the rootsystem may find itself in a position ofreduced sink strength due to apical domi-nance (cf. 73) under vigorous foliar growthconditions during the vegetative season.As soon as the above-ground vegetativedominance and the normal assimilate dis-tribution pat tern between leaves andbunches (20,21,36,52,74) are changed by

partial defoliation, the roots may haveaccess to assimilator y reserves and recent-ly produced photosynthates in the phloemwhich effectively neutralize possible stressconditions imposed by partia l defoliation.

However, the physiological significance of tar tar ic acid2.0-rem ain s enigmati c (55). After defoliating vines from ~,

budburst onwards, Marangoni e t a l (47) suggested th at wc a r b o h y d r a t e s and organic acids occurring in the xylem Esap in the pre-bloom growth phase were derived largely ~ 1 . 5 -from plant reserves. Whether tartar ic acid is transport-ed to the new growth areas in spring and wheth er it is ~ -

available for accumul ation in the berries are open to ~ 1.0-speculation.O

Althou gh none of the sugar s or organic acid levels owere significantly affected by part iall y defoliating vines 8 0.5 -melevated concent rations were found for most compounds(Fig. 4 and 5). Pr ema tur e and severe defoliation of ograpevines causes mobilization of stored carbohydrate 0 . 0reserves from roots, trunks, and canes and inducesstress conditions, as indicated by decreases in yield,lower bud fertility in the following season, delayedripening, and reduction in dry weight and carbohydrate

Ta r t a r i c a c i d C i t r i c a c i d

BB Control][---1 *Pe as i z e d e f o l i a t i o n

* Ve r a i s o n d e f o l i a ti o nI

a

a a__

a

M a l i c a c i dFig. 5. Effect of 33% defoliat ion o f the grap evine on root organic acid co*Defoliat ion in the lowe r half of the cano py; prece ded by defoliat ionbunch zone at berry set. Values de signated by the sam e let ter do not dsignificantly (p < 0.05) for each acid.

A m . J . Enol . V i t ic . , Vol . 46 , No. 3 , 1995


6/9

PARTIAL DEF OL IAT ION 311

Table 3 . Effect of 33 defol ia t ion of grapevineson canopy character is t ics and vine performance.

Tr e a t m e n t

Pa r a m e t e r C o n t r o l ~ Pe a - s i ze ~ Ve r a i s o nd e f o l i a t i o n d e f o l i a t i o n

2Canopy gaps ( ) 10 - 20 50 452Canopy densi ty index >2 ,,oc 4Jo

L_

oJo2 0 - - ~ n 0

Fig. 8 . Effect of 33 defol ia t ion on wine qual i ty. *Defol ia tion in the loweof the canopy; pre ceded by defol ia t ion in the bunch z one a t berry se t .

C a n o p y effi cien cy: Canopy gaps, fruit light expo-sure, and number of leaf layers of partially defoliatedvines Table 3) were in accordance with para mete rsrecommended for the production of highe r quality grape s62,64). The results also imply that the incidence of

pests and diseases would be reduced and chemicalcontrol would benefit from part ial defoliation 4,38,67,76).Both defoliation tre atment s significantly improved lightinte nsit y in the interior of the canopy Table 3). Thiscertainly contributed to the higher photosynthetic ac-tivities of middle and ba sal leaves Fig. 6), confirming

A m . J . E n o l . Vi t ic . , Vo l . 4 6 , N o . 3 , 1 9 9 5


7/9

3 12 - - H U N T E R e t a L

the sti mula ting effect of part ial defoliation (15,22,39)and the deleterious effect of interior- canopy shade onphotosynthetic response (22,37,48,62).

Yi e l d p a r a m e t e r s Since the period just prior tobloom is critical in determin ing the numbe r of bunchesper bud (1), it is rem ark able th at defoliation at pea-sizeand veraison (and concomitant higher light intensityreceived by the basal buds) can ap pare ntl y still increasebud fertility (Table 3), unless the initial defoliation inthe bunch zone at berry set stage benefited conversionof anlagen to inflorescences instead of tendril primor-dia. The more shaded in terio r of the non-defoliatedvines probably also impeded nutrient supply from theleaves to the buds, decreasing bud fertility and buddingcapacity (Table 3).

Notwi thstand ing the 23 and 44 less leaf area/gfresh berry mass at ripeness (Table 3), partially defoli-ated vines produced approx imate ly 11 and 59 high eryields after defoliation at pea-size and verai son, respec-tively (Table 3). This is in contrast to previous resultswith severe defoliation (24,30) and further proves thatenhance d mobilization of carbohy drate reserves as aresul t of part ial defoliation as suggested earl ier (30), isvery unlikely under the conditions of this experiment.Lower and more favorable source:sink ratios creat ed bypartial defoliation as well as the improved canopy mi-croclimate favoring metabolic activity of both leavesand grapes are a more obvious explanation. The stimu-lation of yield and photos yntheti c activity is all the moreremarkable because the major part of defoliation tookplace during the time of decreasing canopy photosyn-thesis (19,40) and passive root growth (71). In line wi thprevious results (25), cane mass was little affected bypartial defoliation; however, early defoliation reducedshoot growth, compared to lat er defoliation (Table 3). In

general, the results coincide with data for variousrootstocks under different cultural practices that rootdensity, yield, and cane mass are closely related(18,68,71).

G r a p e c o m p o s i t i o n a n d w i n e q u a l i t y Part ialdefoliation had no effect on total soluble solid accumu-lation in the fruit, but increased titratable acidity andreduced must pH (Table 4). Apparently, meaningfulincreases in both wine composition (Fig. 7) and winesensory data (Fig. 8) were found when vines werepartially defoliated.

G e n e r a l Reasons for the improved performance ofpartially defoliated vines were discussed in previouspapers (16,17) and were mostly related to the fact thatan inferior canopy microclimate caused by excessivefoliage is in a direct and in direct way de tri ment al to thegeneral m etabol ism of vines. Supply (via photosynthe-sis) and demand [via respiration, cell division and/orenlargement, and storage (14)] under warm and coolclimates (31,35,37,62,64,65) are affected, resulting invines functioning below their individual ma ximu m po-tential/efficiency.

C o n c l u s i o n s

Although the root system was relatively insensitive

to defoliation as applied in this study, the tendentiousstim ulat ion of root growth and root syst em efficiencyindicate a fine balance between above-ground and sub-terranean growth. Considering the much lower leafarea per gram fresh berry mas s of partially defoliatedvines as compar ed to th at of non-defoliated vines, it isevident th at perform ance of leaves in supplying photo-synt hat es for growth a nd development depend to a large

extent on microclimate and source:sink ratio. This indi-cates that the generally observed relationship betweenabove-ground and subte rran ean growth of grapevinesis very impo rta nt in the control of general metabol ism,soil utilization, yield, and wine quality and can bepositively mani pulated by careful canopy management.

It is evident that the increase in photosyntheticactivity of rem aini ng leaves after par tial defoliation wassufficient to sustain or even increase normal growth ofthe root system. The homeostatic mechanism by whichthe balance between shoot and root output (size Xactivity) is maintained (44,54) was obviously not dis-rupted. The results indicate that higher carbon fixationrates ensured high export from sources and utilizationin sinks and v i c e v e r s a 1 2 , 1 3 , 1 4 , 6 9 ) .Growth regulatorsmay play an impor tant role in their control of thisrelati onship (74). I t would seem as if both the rootsystem and the canopy increased their efficiency inresponse to partial defoliation. As suggested earlier(23), senescence of rem aini ng leaves on part ially defoli-ated vines may be inhibited, which is important in thelight of the elevated sucrose production in leaves andtheir presumed contribution to storage pools, particu-larly after harvest (19).

All factors investigated point to the fact that dis-criminat ive defoliation as applied in this study does notimpede grapevines in any way. On the contrary, plant

performance was improved to such an extent that par-tial defoliation mus t be considered a necessity for vigor-ously growing grapevines in a given situation. Themanipulations have no deleterious effects on the envi-ronment and the vines retain normal allocation pat-terns, which is important for continued health andlongevity parti cular ly of perenni al plant s such as thegrapevine.

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