Physiology of Flowering in the Grapevine

7/25/2019 Physiology of Flowering in the Grapevine

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P H Y S I O L O G Y O F F L O W E R I N G IN T H E G R P E V I N E

R E V I E W

Chinnathambi Srinivasan and Michael G. Mullins

Respectively Research Fellow and Professor of Horticulture, Department of Agronom y and Hor-

ticultural Science, University of Sydney, Sydney, N .S.W . 200 6, Australia. Present address of the

senior author: Department of Environmental Horticulture, U niversity of California, Da vis, California

95616.

Research on flowering in the grapevine at the University of Sydney is supported by the Rural

Credits Development Fun d, Reserve Ba nk of Australia. We thank J. F. Sutcliffe Annals of Botany

Com pany for permission to reprodu ce Figures 1C, D; 2 Stages 0, 2, 3); 3 Stages 4, 5, 7) and 4

Stage 8).

Manuscript submitted 3 September 1980.

Revised manuscript received 10 December 1980.

Accepted for publication 10 December 1980.

ABSTRACT

The vegetative and reproductive an atomy of the

grapevine is discussed with emphasis on recent in-

terpretations based on scanning electron microscopy.

The terminology of flowering in i t i s is defined and a

developmental code, comprising Stages 0 to 11, is pro-

posed for the event s leading to formati on of flowers. In

brief, flowering in the grapevine involves three main

steps: 1) Forma tion of Anlag en or uncommit ted

primo rdia (Stages 0 to 1); 2) Differentiation of Anlagen

to form inflorescence primordia (Stages 2 to 7); and 3)

Differ entiatio n of flowers (Stages 8 to 11). The liter a-

ture on the factors that influence flowering in grapes is

reviewed under three major headings: 1) Biochemical

changes in apices during inflorescence primordia for-'

mation; 2) Effects of envir onme ntal factors, includ ing

temperature, light intensity, photoperiod, water stress

and mine ral nutr iti on and 3) Role of phytohormones.

Anlagen develop into inflorescences, tendrils or

shoots depending on the environment and hormonal

factors. A hypothetical scheme for the hormonal con-

trol of Anlagen, tendri l and inflorescence formatio n is

proposed. It is suggested that flowering in grapes is

controlled by the gibberellin:cytokinin balance. For-

mati on of the inflorescence axis (the Anlage) is gib-

berellin controlled, but subsequent differentiation into

flowers is regulated by cytokinin.

The origin and development of inflorescences and

flowers in the grapevine have been studied for more

tha n a centur y (84) but res earch on the control of flow-

ering has a sho~t history. In 1971 Prat t (118) published

an authoritative review on the reproductive anatomy

of cultiv ated grapes, bu t she did not discuss the ea rly

stages of inflorescence inception or the factors which

affect inflorescence formation. Subsequently, Buttrose

(33) reviewed only t he influence of climate on flower-

ing. The present review is concerned with the

mechanisms by which apices are transformed from the

vegetati ve to the reproduct ive mode of development.

V E G E T T I V E N D R E P R O D U C T I V E

N T O M Y O F T H E G R P E V I N E

The grapevine is a complex plant and opinions dif-

fer as to the naming of its parts. An abridged descrip-

tion of grapevine anat omy will be given here, th e ob-

jects of which are to introduce t he term inology and to

set the scene for later discussion of the physiology of

flowering.

Origin of the pr omp t bu d a nd la t eral shoot- The

first bud which arises in the axil of the leaf subtended

by a curr ent season's shoot is known as the prompt

bud (prompt bourgeon) (Fig. 1A). This bud has the

characte ristic of growing out in the same season as its

formation, and the lateral shoot so formed is known in

French as the entre coeur (124). Pra tt (119) called

this outgrowth the summer lateral. The lateral shoot

seldom bears inflorescences but there are varietal dif-

ferences in this regard (124). Huglin (57) showed that

the growth of the lateral shoot is inhibited by the apex

of the main or primary shoot. If this correlative inhibi-

tion is removed, the later al shoot develops into a vigor-

ous fertile shoot (13).

The la te nt bud. The first leaf of the lateral shoot is

reduced to a bract or prophyll (35). The bud which

develops in the axil of the bract is the la te nt bud

(bourgeon latent, Fig. 1 B). The latent bud grows

slowly within the bract. Depending on the cultivar the

latent bud produces 6 to 10 leaf primordia and up to

three inflorescence primordia before becoming dor-

mant during the winter. Although the latent bud is

establis hed as an appendage of the la teral shoot, its

association with the primary shoot is very close. The

xylem vessels of the you ng lat ent bud lead directly to

the p rim ary shoot, but not directly to the xylem of the

lateral shoot (84,119). Prillieux (120) was the first to

discover that the latent bud of the vine does not adjoin

the ma in shoot but arises as the axill ary bud of the first

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A m . J . E n o l . V i t i c . V o l . 3 2 N o . 1 1 9 8 1


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4 8 - - F L O W E R I N G IN G R A P E V I N E

bract-lik e leaf of the l ateral shoot. This relat ionshi p

was confirmed by Mdlle r-Thur gau 94) and has been

discussed by several more recen t author s 25,

35,84,146).

Secondary and tert iary la tent buds: The apex of

the pri mar y lat ent bud produces two or more bracts

before producing leaf primordia. The buds in the axils

of these two bracts are t he secondary and te rti ary la-

tent buds. These buds exhibit limited growth and they

produce mainly leaf primordia. The secondary buds

may form inflorescence primordia in some cultivars.

The terti ary buds usually remain vegetative 119).

Fig . 1 . Format ion o f the la ten t bud, lea f p r imord ia and s t ipu le p r imord ia in the grapevine .

A. The promp t bud PB) is cover ed by a bract BR). The la ten t bud LB) is fo rme d in the ax i l o f the f irs t b ract . In th is p repara t ion the f i rs t b ract has

been rem oved to expo se the la ten t bud in i t ia l LB). Note the promine nt scar o f the bract BR).

B. A la te r s tage in fo rm at ion o f the la ten t bud the prom pt bud has been rem oved). Th e la ten t bud LB) has fo rmed a bract and the f i rs t lea f

pr imord ium LP1).

C. Di f fe ren t ia t ion o f the f irs t lea f p r imo rd ium LP). S t ipu le p r imord ia St ) a re fo rme d f rom the flanks o f the lea f p r imord ium. A) - la ten t bud apex.

D. A la ten t bud in wh ic h th ree lea f p r imo rd ia hav e been fo rme d LP1, LP2 and L P3). Note the inc ip ien t s t ipu les St ) on e i ther s ide o f the

n e w ly - f o rme d le a f p r imo rd iu m L P ) .



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F L O W E R I N G

IN

G R A P E V I N E m 9

T h e p r i m a r y , s e c o n d a r y a n d t e r t i a r y b u d s , w h i c h

a r e e n c l o s e d b y t h e b r a c t o f t h e l a t e r a l s h o o t a n d b y t h e

t w o b a s a l b r a c t s o f t h e p r o m p t b u d , c o n s t i t u t e t h e w i n -

t e r b u d o r e y e (l 'o e il ) o f t h e d o r m a n t c a n e ( m a t u r e

g r a p e s h o o t) . T h e e y e i s a c o m p o u n d o r m i x e d b u d

a n d i t c o n s i s t s o f s e v e ra l b u d s , t h e o n e l o c a t e d i n t h e

a x i l o f t h e o t h e r .

F l o w e r i n g i n t h e g r a p e v i n e : T h e f or m a t io n o f in -

f l o r e s c e n c e s a n d f l o w e r s i n t h e g r a p e v i n e i n v o l v e s

t h r e e w e l l - d e f i n e d s t a g e s ( 8 , 1 8 , 1 9 , 2 5 , 2 6 , 3 6 , 8 4 , 1 1 4 ,

147).

For mat ion o f An lag en s ingu lar - An lage) : A n l a g e n

a r e c l u b - s h a p e d m e r i s t e m a t i c p r o t u b e r a n c e s w h i c h

a r i s e f r o m t h e a p i c e s o f l a t e n t b u d s . A n l a g e n a r e u n -

c o m m i t t e d p r i m o r d i a w h i c h m a y b e d i r e c t e d t o f o r m

i n f l o r e s c e n c e p r i m o r d i a , t e n d r i l p r i m o r d i a o r s h o o t

p r i m o r d i a . F o r m a t i o n o f A n l a g e n i s a ls o r e f e r r e d t o i n

t h i s r e v i e w a s i n f l o r e s c e n c e i n i t i a t i o n o r i n f l o r e s c e n c e

a x i s fo rm a t i o n (F i g . 2 ) .

F o r m a t i o n o f i n fl o re s ce n c e p r i m o r d i a : A n l a g e n

w h i c h h a v e b e e n d i r e c t e d t o d e v e l o p a s i n f l o r e s c e n c e s

u n d e r g o r e p e a t e d b r a n c h i n g t o fo r m a c o n ic a l s t r u c t u r e

c o m p o s e d o f m a n y r o u n d e d b r a n c h p r i m o r d i a ( F i g . 3) .

Form ation of f lowers: D i f f e r e n t i a t i o n o f i n f lo r e s -

c e n c e p r i m o rd i a t o fo rm t h e i n d i v i d u a l f l o we r s (F i g . 4 ) .

T h e f i r s t t w o s t a g e s a r e c o m p l e t e d d u r i n g t h e c u r -

r e n t s e a s o n . T h e f i n a l s t a g e , f l o w e r f o r m a t i o n , o c c u r s

s h o r t l y b e f o re a n d d u r i n g b u d b u r s t i n t h e n e x t s p r i n g .

F u l l y m a t u r e l a t e n t b u d s c o n t a i n i n g o n e o r m o r e

i n f l or e s c e n c e p r i m o r d i a a r e c a l l e d f r u i t f u l o r f e r t i le

b u d s . T h i s c o n d i t i o n o f l a t e n t b u d s i s k n o w n a s f r u i t -

f u l n e s s o r fe r t i l it y . U n f r u i t f u l , i n f e r t i l e o r v e g e t a t i v e

b u d s a r e l a t e n t b u d s w h i c h c o n t a i n t e n d r i l p r i m o r d i a

i n t h e p l a c e o f i n f l o re s c e n c e p r i m o r d i a . T e n d r i l s , w h i c h

a r i s e i n a s p e c i f i c s e q u e n c e i n l e a f -o p p o s e d p o s i t i o n s ,

a r e p r o d u c e d b y t h e a p i c e s o f p r i m a r y s h o o ts , l a t e r a l

s h o o t s a n d p r i m o r d i a l s h o o t s o f l a t e n t b u d s . T h e l a t e r a l

m e r i s t e m s w h i c h g i v e r i s e t o t e n d r i l s a r e a l s o c a l l e d

A n l a g e n r e g a r d l e s s o f t h e k i n d o f s h o o t f r o m w h i c h

t h e y o r i g i n a t e . A n l a g e n w h i c h a r i s e d i r e c t l y o n m a i n

a n d l a t e r a l s h o o ts o f t h e c u r r e n t s e a s o n d o n o t u s u a l l y

f o r m i n f l o r e s c e n c e s a n d t h e y r e m a i n a s t e n d r i l s , b u t

m o s t A n l a g e n w h i c h a r e i n i t i a t e d i n l a t e n t b u d s g i v e

r i s e t o i n f l o r e s c e n c e s . I t h a s b e e n d e m o n s t r a t e d t h a t

A n l a g e n a n d y o u n g t e n d r i l s o n m a i n a n d l a t e r a l s h o o ts

h a v e t h e p o t e n t i a l t o fo rm i n f l o r e s c e n c e s (1 4 8 ,1 4 9 ,1 5 0 ) ,

b u t t h i s p o t e n t i a l i s s e l d o m e x p r e s s e d d u e t o c o r r e l a -

t i v e i n h i b i t i o n b y t h e r e s p e c t i v e s h o o t a p ic e s . C o r r e l a -

t i v e i n h i b i t i o n i s u n d e r t h e c o n t r o l o f h o r m o n e s ( 11 5 ).

W h e n A n l a g e n a n d t h e i r d e r i v a t i v e s , t h e y o u n g t e n -

d r i l s , a r e f r e e d f r o m c o r r e l a t i v e i n h i b i t i o n b y t r e a t -

m e n t w i t h e x o g e n o u s g r o w t h s u b s t a n c e s , o r b y e x c i s io n

a n d c u l t i v a t i o n in vitro w i t h t h e a p p r o p r i a t e p l a n t

h o r m o n e s , t h e y g i v e r i s e to i n f l o r e s c e n c e s ( 1 4 8,

149 ,150) .

D E V E L O P M E N T A L S T A G E S I N T H E

F L O W E R I N G O F G R A P E V I N E S

A n a c c u r a t e d e s c r i p t io n o f t h e m o r p h o l o g i c a l

c h a n g e s i n b u d s d u r i n g t h e f o r m a t i o n o f i n f l o r e sc e n c e s

a n d f l o w e r s i s a n o b v i o u s p r e r e q u i s i t e t o t h e u n d e r -

s t a n d i n g o f p h y s i o lo g i c a l c o n t r o ls i n t h e f l o w e r i n g p r o -

cess .

H i t h e r t o , m u c h o f t h e i n f o r m a t i o n o n th e f o r m a t i o n

o f i n f l o r es c e n c e s a n d f l o w e r s i n t h e g r a p e v i n e h a s b e e n

a c c u m u l a t e d f r o m s t u d i e s o f m e d i a n l o n g i t u d i n a l s ec -

t i o n s o f p a r a f f i n - e m b e d d e d l a t e n t b u d s ( 1 9, 35 ) . W i t h a

c o m p l e x t h r e e d i m e n s i o n a l s t r u c t u r e s u c h a s a l a t e n t

b u d t h e u s e o f s e c t io n s f o r t h e s t u d y o f d y n a m i c a s p e c t s

o f g r o w t h a n d d e v e l o p m e n t i s l a b o r i o u s a n d p r o n e t o

e r r o r . T h e i n t e r p r e t a t i o n o f s e c t io n s c u t f r o m b l o c k s

w i t h d i f f e r i n g o r i e n t a t i o n s i s o f t e n e x c e e d i n g l y d i f -

f i c u l t . F o r e x a m p l e , o n l y s e c t i o n s wh i c h b i s e c t t h e l a -

t e n t b u d a p e x a l o n g t h e p l a n e o f l e a f a n d i n f l o r es c e n c e

p r i m o r d i u m f o r m a t i o n w i l l sh o w s o m e p a r t s o f b o t h

l e a f a n d i n f l o re s c e n c e p r i m o r d i a ( 3 5, 1 82 ) . T h e s c a n -

n i n g e l e c t r o n m i c r o s c o p e ( S E M ) i s a n i d e a l i n s t r u m e n t

f o r i n v e s t i g a t i o n s o f b u d s t r u c t u r e b e c a u s e i t e n a b l e s

o b s e r v a t i o n s t o b e m a d e a t h i g h m a g n i f i c a t i o n a n d

w i t h g r e a t d e p t h o f f o cu s .

T h e c o m p l e x m o r p h o l o g y o f t h e g r a p e v i n e s h o o t

s y s t e m a n d t h e o r i g i n o f i n f l o r e sc e n c e s h a v e b e e n

c l a r i f i e d r e c e n t l y b y s c a n n i n g e l e c t r o n m i c r o s c o p y

(1 47 ) . As a n e x t e n s i o n o f t h i s w o rk , a n d a s a n a i d t o

d e s c r i p t i o n , a d e v e l o p m e n t a l o r p h e n o l o g i c a l c o d e fo r

f l o w e r i n g i n t h e g r a p e v i n e h a s b e e n c o n s t r u c t e d ( 1 4 6 )

i n wh i c h t h e v a r i o u s s t a g e s (0 t o 1 1) a r e r e l a t e d t o

c h a n g e s i n t h e s h a p e o f o i~ g an s o r to t h e a d d i t i o n o f n e w

s t r u c t u r e s ( F i g s . 2 - 4 ) . S i m i l a r d e v e l o p m e n t a l c o d e s

h a v e b e e n p r o p o s e d f o r f l o w e r i n g i n X a n t h i u m (127)

a n d r o s e s ( 5 6 ) , u s i n g i n f o r m a t i o n f r o m l i g h t m i -

c ro s c o p y , a n d fo r wh e a t (1 0 6 ) u s i n g S E M .

I n t h e p r o p o s e d c od e fo r f l o w e r i n g i n t h e g r a p e v i n e

t h e l a t e n t b u d a p e x i s c o n s i d e r e d t o b e i n a v e g e t a t i v e

c o n d i t i o n u n t i l t h e i n i t i a t i o n o f t h e f i r s t A n l a g e . A c -

c o r d i n g l y , a p i c e s c o n t a i n i n g l e a f p r i m o r d i a o n l y a r e r e -

f e r r e d t o a s S t a g e 0 . T h e c l e a v a g e o f t h e a p e x t o f o rm

t h e A n l a g e i s d e s i g n a t e d S t a g e 1. L a t e r s t a g e s a r e

n u m b e r e d s e r i a l l y a c c o r d i n g to t h e e x t e n t o f t h e

r a m i f i c a t i o n o f t h e A n l a g e n ( F i gs . 2 , 3, 4) . R e f e r e n c e

wi l l b e m a d e t o t h i s c o d e i n t h e fo l l o wi n g d i s c u s s i o n o n

d e v e l o p m e n t o f p r i m o r d i a i n l a t e n t b u d s .

F O R M A T I O N O F P R I M O R D I A I N T H E

P R I M A R Y L A T E N T B U D

L e a f p r i m o r d i a T h e f o r m a t i o n o f a l e a f p r i m o r -

d i u m a t t h e f l a n k o f t h e l a t e n t b u d a p e x i s t h e f i r s t s te p

i n t h e d e v e l o p m e n t o f t h e b u d ( F ig . 1 B , C ). L e a f

p r i m o r d i a a r i s e f r o m t h e a p i c a l m e r i s t e m i n a c r o p e t a l

s u c c e s s i o n a n d w i t h d i s t i c h o u s p h y l l o t a x y ( 3 5 , 1 4 7 )

( F ig . 1 D ). A s s o c i a t e d w i t h e a c h l e a f p r i m o r d i u m a r e

t wo o v o i d s t i p u l a r s c a l e s (F i g . 1 C , D) . T h e s e s c a l e s a r e

l o c a te d o n e o n e i t h e r s i d e o f t h e l e a f p r i m o r d i u m . I n i -

t i a l l y t h e s c a l e s a r e a s b i g a s l e a f p r i m o r d i a b u t t h e y

s o o n s t o p g ro wi n g a n d b e c o m e s c l e r i f i e d (1 9 ,1 4 6 ,1 8 2 ) .

T h e l e a f p r i m o r d i a a r e p o i n t e d s t r u c t u r e s w h i c h b e -

c o m e l o b e d a t t h e i r b a s e s a n d r a p i d l y a s s u m e a l e a f -

l i k e a p p e a r a n c e ( F ig . 1 D ). T h e f i r s t tw o o r t h r e e l e a f

p r i m o r d i a g r o w r a p i d l y a n d e n v e l o p t h e s u b s e q u e n t

p r i m o r d i a . T h e l a t e r - f o r m e d l e a f p r i m o r d i a a r e r e l a -

t i v e l y s lo w g r o w i n g a n d t h e y r e m a i n s m a l l ( 1 4 6) . H a i r s

A m . J . E n o l . V i t ic . V o l . 3 2 N o . 1 1 9 8 1


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F L O W E R I N G I N G R A P E V I N E m 5 1

S ta g e 4 . D iv i s io n o f t h e A n la g e t o f o rm a n in n e r a rm IA ) a n d a n

o u te r a rm OA ) . Th e in n e r a rm b e co m e s t h e ma in a x is o f t h e in f lo re s -

ce n ce a n d t h e o u te r a rm b e c o me s t h e p ro x ima l b ra n ch o f t h e in f lo re s-

ce n ce .

Stage 5 . Grow th o f the main a x is inner a rm) to g ive r ise to the fi rs t

b ra n ch p r imo rd iu m B P ) .

Stag e 6 . Gro wth o f the main axis o f the i n f l o re sce n ce p r imo rd iu m to

fo rm se ve ra l b ra n ch p r imo rd ia B P ) a n d b ra c t p r imo rd ia B R) .

Stage 7 . Di f fe ren t ia t ion o f the branch pr imord ium a t bud burst and

forma t ion o f the f lower in i t ia ls FI ) . Note group o f f ive f lowe r in i t ia ls .

F ig . 3 . Deve lopmenta l s tages in the f lower ing o f

i t i s v i n i f e r a

L . - - f o rma t io n o f i n f l o re sce n ce p r imo rd ia .

Am . J . En o l . V i t ic . Vo l . 32 No . 1 1981


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FLOWERING IN GR AP EV IN E 53

develop from the up per epiderm al cells of leaf and scale

primordia and produce a tomentum which encases each

whorl of leaves 146). The basal leaf primordia, stipu-

lar scales and tomentum all provide a protective cover

for the meri stematic apex of the l atent bud.

In the cultivar Sul tana, growth of laten t buds

ceases after the formation of 12 to 13 leaf primordia

19) but some cultivar s of central Euro pean origin, for

example, Gutedal 186), Riesling and Auxerrois 57),

and Freis mer 84), produce less th an 12 leaf primor dia

before the latent bud becomes dormant.

Anlagen: Depending on the cultivar the latent bud

apex produces three to eight leaf prim ordia Fig. 2,

Stage 0) and then divides into two almost equal parts

8,118,146). The part opposite the youngest leaf

prim ordi um is the Anlage Fig. 2, Stage 1). The forma-

tion of Anlag en from the apex is the earliest indication

of reproductive gr owth in the grapevi ne and t he forma-

tion of the An lage can be regarded as the stage of initi-

atio n of the inflorescence axis 84,147).

Initiall y, the two part s of the divided apex Anlage

and laten t bud apex) have a simil ar appearance Fig. 2,

Stage 1) but t hey soon acquire different conformations.

Anlagen develop as broad, blunt, obovate structures

and they lack stipul ar scales Fig. 2, Stage 2). Leaf

primordia are narrow pointed structures and arise

from the fl ank of the apex Fig. 2, Stages 0, 1).

Brac ts and arms: The further development of the

Anlag en start s with the formati on of a bract 182).

Bracts or iginate as depressions in the distal ends of the

Anlagen. Later, these depressions appear to move to

the periphery and to form a collar-like structur e Fig.

2, Stage 3). The Anlage then divide into two unequal

parts, called arms. The larger adaxial part nearer to

the apex) is the inner arm, and the smaller abaxial

part adjoi ning the bract is the outer ar m Fig. 3, Stage

4) 118,147).

Inf lo rescence pr imord ia format ion : In f lo res -

cence primord~a are formed by extensive branching of

the Anlag e Fig. 3, Stage 5). The inner ar m divides and

produces several globular branch primordia 133)

which give rise to the main body of the inflorescence.

Bran chin g of the outer arm is less extensive and it

develops into the lowest branch of the inflorescence

84). The branch pr imordi a of the in ner an d outer arm s

give rise to branch primo rdia of the second and third

order, each of which is subte nded by a bra ct Fig. 3,

Stages 6 and 7). The degree of bran chin g of the inner

arm gradually decreases in an acropetal direction and

this gives the inflorescence primord ium a conical shape

Fig. 3, Stage 7). The appearance of a fully-developed

inflorescence primordium is rather like a bunch of

grapes in which each berry-like branch primordium is

a protuberance of undifferentiated meristematic tissue

Fig. 3, Stage 7). After the format ion of one-to three

inflorescence primor dia depending on the cultivar),

the late nt bud enters into dormancy 118).

D I F F E R E N T I T I O N O F F L O W E R S

According to most reports the differentiation of

flowers from inflorescence primordia begins after the

dormant la tent buds are activated in the spring

2,19,128,144,182). However, Alleweldt and Balkema

8) and Alleweldt and Ilter 10) have suggested that a

large proportion of floral merist ems may form sepals in

the late sum mer preceding the season of flowering, but

such early differen tiation of flowers has not been con-

firmed in more recent studies with the scanning elec-

tron microscope 133,146).

Each bra nch p rimo rdiu m of inflorescence primor-

dium divides many times and ultimately it produces

the flower ini tia ls Fig. 4, Stage 8). There are differ-

ences among cultivars in regard to the differentiation

of flowers. In Muscat of Alex andr ia and Thompson

Seedless the flower primordia are formed in groups of

thr ee 88,113), but in Shiraz the flowers occur in

groups of five 146; Fig. 4, Stage 8).

Initiation and development of flowers parts was

said by Barn ard and Thomas 19) and by Snyder 144)

to occur simult aneou sly in all par ts of the inflorescence

primordium but later workers have disputed that

development of flower parts is synchronous 2,

121,182). It is now clear tha t sepals, petals calyptrae),

s tamens and pis ti ls develop one after the other

118,146) Fig. 4, Sta ges 9,10,11).

The appear ance of the calyx as a continuous ring of

tissue on the rim of the pr esumpt ive flower primor-

dium marks the begi nning of the formation of flower

part s [see Pratt, 118) for review]. The calyx ring does

not coalesce at its tip but forms an incomplete cover

over the petals Fig. 4, Stag e 9). The petals and sta-

mens arise as five papillae soon after the formation of

sepals. The petals do not coalesce at t heir marg ins or at

thei r tips as suggested by Snyder 144), but special

cells are formed at the margins which interlock with

simil ar cells on the marg ins of the adjacent petals to

form a cal ypt ra Fig. 4, Stag e 10) 146,147). At an-

thesi s in a mat ur e flower Fig. 4, Stage 11) the petals

become free first at their prox imal ends bases) and

then separate and curve upwards and outwards to re-

lease the stame ns 118). In cytokinin -treated flowers

the petals open from the top or remain closed as in

cleisto gamous flowers 149). Peta ls and sta men s are

persistent in cytokinin-treated flowers, but are de-

ciduous in normally-pollinated flowers.

BIOCHEMICAL CHANGES IN APICES DURING

THE F O R M T I O N O F INFLORESCENCE

P R I M O R D I

Tre atm ent of grape leaves with uracil increases in-

florescence primor dia format ion 66) and the yield of

grape s 15,63,64). This response was associate d wit h

an increase in nucleic acids and protein synthesis in

leaves. The relat ions hip of nucleic acid change s in

leaves to the yield of grapes is difficult to interpret , but

the nucleic acid stat us of lat ent buds

n s tu

seems to be

related to fruitfulness. The DNA content is high during

Anlage formati on Stage 1) and during the early stages

of inflorescence primor dium fo rmation Stages 2 to 6)

but the RNA content increases before Anlage forma-

tion Stage 0) and again durin g Stages 2 to 6 122).

Addition of nitrog en enhan ces the synthesis of pro-

tein and nucleic acids and this has been related to an



8/17

5 4 FL OWE R I N G IN GR A P E V I N E

i n c r e a s e i n in f l o r e s c e n c e f o r m a t i o n ( 1 ,4 0 ). W h e n

r a d i o a c t i v e P w a s a p p l i e d t o f i v e g r a p e c u l t i v a r s a t

S t a g e 0 , m o s t o f t h e a b s o r b e d 3 2p w a s f o u n d s u b -

s e q u e n t l y i n t h e n u c l e i c a c i d s f r a c t io n o f l a t e n t b u d s

d u r i n g S t a g e s 1 t o 8 (1 5 8 ). T h e s i z e o f n u c l e i i n t h e

i n f l o r e s c e n c e p r i m o r d i a i n c r e a s e s c o n s i d e r a b l y d u r i n g

f l o w e r d i f f e r e n t i a t i o n a t b u d b u r s t ( 8 4 ) . T h e n u c l e i c

a c id s co n t e n t , R N A / D N A r a t i o a n d c a t a l a s e a n d

p e r o x i d a s e a c t i v i t y a r e a l l h i g h e r i n y o u n g s h o o t s ( a t

b u d b u r s t ) b e a r i n g i n f l o r e s c e n c e s t h a n i n v e g e t a t i v e

shoo ts (160) .

H i s t o c h e m i c a l c h a n g e s i n t h e a p i c e s o f l a t e n t b u d s

d u r i n g t h e f o r m a t i o n o f A n l a g e n , i n f l o r e s c e n c e

p r i m o r d i a a n d t e n d r i l p r i m o r d i a w e r e s t u d i e d i n t h e

c u l t i v a r S h i r a z b y S r i n i v a s a n a n d M u l l i n s ( 1 51 ).

P e r i p h e r a l z o n e c e l ls o f l a t e n t b u d a p i c e s s h o w e d m i t o-

t i c a c t i v i t y a n d e n z y m e a c t i v i t y b u t t h e c e n t r a l z o n e

c e ll s a r e q u i e s c e n t . F l u o r i m e t r i c d e t e r m i n a t i o n o f t h e

D N A c o n t e n t o f n u c l e i i n l a t e n t b u d a p i c e s r e v e a l e d a n

i n c r e a s e i n t h e p r o p o r t i o n o f 2 C n u c l e i d u r i n g A n l a g e

f o r m a t i o n a n d d i f f e r e n t i a t i o n . T h i s c o n d i t i o n w a s p a r -

t i c u l a r l y e v i d e n t i n v i n e s g r o w n w i t h 3 0 C d a y t o 25 C

n i g h t t e m p e r a t u r e s , a r e g i m e w h i c h i s f a v o r a b l e f o r

i n f l o r e s c e n c e p r i m o r d i a f o r m a t i o n . I n v i n e s g r o w n a t

1 8 C d a y t o 1 3 C n i g h t , a t e m p e r a t u r e u n f a v o r a b l e f o r

i n f l o r e s c e n c e s fo rm a t i o n , n u c l e i w i t h t h e 4 C l e v e l o c -

c u r r e d w i t h a h i g h f r e q u e n c y i n A n l a g e n . T h e p r e -

d o m i n a n c e o f n u c l e i w i t h t h e 2 C - D N A l e v e l i n d i c a t e s a

r a p i d m i t o t i c t u r n o v e r , b u t p r e d o m i n a n c e o f 4 C - n u c l e i

i s t h e s i g n o f s l o w m i t o t i c a c t i v i t y . C a ro l u s (3 5) a ls o

f o u n d t h a t a h i g h p r o p o r t i o n o f c e l ls i n v o l v e d i n A n l a g e

f o r m a t i o n a r e m i t o t i c a l l y a c t i v e . I n f u l l y m a t u r e d i n -

f l o r e s c e n c e o r t e n d r i l p r i m o r d i a c e l l s c o n t a i n m o s t l y

4 C n u c l e i . T h i s i n d i c a t e s , p e r h a p s , t h a t m i t o t i c a c t i v -

i t y i s s l o w i n g d o w n i n l a t e n t b u d s i n a n t i c i p a t i o n o f

o r g a n i c d o r m a n c y ( 1 4 6 ) .

H i s t o c h e m i c a l t e s t s o n c r y o s t a t s e c t i o n s o f l a t e n t

b u d a p i c e s a n d A n l a g e n s h o w e d i n t e n s e a c t i v i t y o f

a c i d p h o s p h a t a s e a n d p e r o x i d a s e i n t h e p e r i p h e r a l

z o n e c e l l s , i . e . , t h e c e l l s i n v o l v e d i n t h e fo rm a t i o n o f

A n l a g e n a n d i n f l o r e s c e n c e p r i m o r d i a . A c c u m u l a t i o n

o f s t a r c h w a s f o u n d i n t he d i a p h r a g m c e ll s a n d i n

o l d e r l e a f p r i m o r d i a o f l a t e n t b u d s ( 1 52 ) d u r i n g S t a g e s

3 t o 6 .

E N V I R O N M E N T L F C T O R S IN F L O W E R I N G

T e m p e r a t u r e : T h e r e a r e m a n y r e p o r ts o f a r e-

q u i r e m e n t f or h i g h t e m p e r a t u r e s f or in f l or e s ce n c e

p r i m o r d i u m f o r m a t i o n i n g r a p e s ( 6 , 1 6 , 3 3 , 5 7 , 1 4 6 ) . A

c l o s e p o s i t i v e c o r r e l a t i o n ( r = 0 .8 2) wa s e s t a b l i s h e d

b e t w e e n m e a n a i r t e m p e r a t u r e a n d t h e p e r c e n t a g e o f

f ru i t i n g s h o o t s (4 5 ) . I n p a r t i c u l a r , t h e r e i s a p o s i t i v e

r e l a t i o n s h i p b e t w e e n t e m p e r a t u r e f r o m t h e m i d d le o f

J u n e t o t h e m i d d l e o f J u l y ( n o r t h e r n h e m i s p h e r e ) a n d

t h e n u m b e r o f i n f l o r e sc e n c e s a p p e a r i n g o n t h e s h o o t i n

t h e fo l l o wi n g s e a s o n (6 ) . S p e c i f i c a l l y , h i g h t e m p e ra -

t u r e s d u r i n g S t a g e s 5 to 7 o f l a t e n t b u d d e v e l o p m e n t

a r e c l o s e l y c o r r e l a t e d w i t h s u b s e q u e n t f r u i t f u l n e s s o f

l a t e n t b u d s (1 6 ) .

I t i s v e ry d i f f i c u l t t o d e m o n s t r a t e a s p e c if i c ef f e c t o f

t e m p e r a t u r e o n f l o w e r f o r m a t i o n u n d e r v i n e y a r d c o n -

d i t i o ns . T o c i r c u m v e n t t h i s d i f f i c u l t y B u t t r o s e

( 2 8 , 2 9 , 3 0 ) u s e d g r a p e v i n e s g r o w n i n s m a l l c o n t a i n e r s

i n c o n t r o l le d e n v i r o n m e n t s . A f t e r t h r e e m o n t h s o f

g r o w t h , t h e l a t e n t b u d s w e r e d i s s e c t e d u n d e r a

s t e r e o m i c ro s c o p e , a n d t h e s i z e a n d we i g h t o f i n f l o r e s -

c e n c e p r i m o r d i a w e r e m e a s u r e d . W i t h t h e r e l a t i v e l y

f r u i t f u l c u l t i v a r , M u s c a t o f A l e x a n d r i a , t h e n u m b e r o f

i n f l o r e s c e n c e p r i m o r d i a r e c o g n i z a b l e a t t h r e e m o n t h s

v a r i e d f r o m z e r o a t 2 0 C to a m a x i m u m o f 1 .6 i n v i n e s

g r o w n a t t e m p e r a t u r e s c l o s e t o 3 5 C ( 2 8 ) .

A p u l s e o f o n l y f o u r h o u r s p e r d a y ( o r n i g h t ) o f h i g h

t e m p e r a t u r e ( 30 C ) w a s s u f f i c i e n t to i n d u c e a

m a x i m u m n u m b e r o f i n f lo r e sc e n c e p r i m o r d i a ( S t a g e 7 ).

T h e c r i t i c a l p e r i o d f o r s u s c e p t i b i l i t y t o t h e h i g h t e m -

p e r a t u r e r e s p o n s e i s t h e t h r e e w e e k s b e f o r e t h e f o r m a -

t i o n o f A n l a g e n b y t h e a p i c e s o f l a t e n t b u d s ( 2 9, 31 ) .

S u b s t a n t i a l d i f f e r e n c e s h a v e b e e n f o u n d i n t e m p e r -

a t u r e r e q u i r e m e n t s f or i n f l o re s c e n c e p r i m o r d i u m f o r -

m a t i o n a m o n g c u l t i v a r s o f d i f f e r e n t g e o g r a p h i c o r i g in

(2 3 ,3 2 ,6 9 ,7 0 ,7 1 ,1 6 2 ) . R i e s l i n g a n d S h i r a z i n i t i a t e i n -

f l o re s c e n c e s w i t h t e m p e r a t u r e s a s l ow a s 2 0 C b u t

M u s c a t o f A l e x a n d r i a r e q u i r e s a t e m p e r a t u r e o f 2 5 C

( 3 2, 11 3 ). C a b e r n e t S a u v i g n o n r e q u i r e s a lo w e r t e m -

p e r a t u r e s u m m a t i o n f o r f l o w e r i n g t h a n B o l g a r o r

R k a t s i t e l i ( 2 3 ) . A h i g h t e m p e r a t u r e p u l s e i s e s s e n t i a l

f o r t h e i n i t i a t i o n o f t h e s e c o n d a n d t h i r d i n f l o re s c e n c e

i n m a n y c u l t i v a r s , i n c l u d i n g c o o l c l i m a t e c u l t i v a r s .

S u l t a n a a n d O h a n e z a r e l e s s f r u i t f u l t h a n m o s t o t h e r

c u l t i v a r s a n d a r e m o r e r e s p o n s i v e t o c h a n g e s i n t e m -

p e r a t u r e ( 32 ). A m e r i c a n c u l t i v a r s ( i n te r s p e c if i c h y -

b r id s ) s u c h a s D e l a w a r e p r o d u c e i n f l o r e s c e n c e s a t

l o w e r t e m p e r a t u r e s ( 21 t o 2 2 C ) t h a n d o v i n i f e r a c u l -

t i v a r s (2 7 t o 2 8 C fo r M u s c a t o f A l e x a n d r i a ) .

L i g h t i n t e n s i t y : E f f e c ts o f l i g h t i n t e n s i t y o n t h e

f r u i t f u l n e s s o f g r a p e v i n e b u d s a r e i n d e p e n d e n t o f t h e

t e m p e r a t u r e r e g i m e ( 3 1 ). T h e e f fe c t o f l i g h t i n t e n s i t y

o n i n f l o r e s c e n c e f o r m a t i o n h a s b e e n s t u d i e d i n t h e

v i n e y a r d i n r e l a t i o n t o t h e h o u r s o f s u n s h i n e ( 16 ) or to

s h a d i n g t r e a t m e n t s ( 8 7 ) . M o s t s t u d i e s h a v e i n d i c a t e d

t h a t s h a d i n g r e d u c e s f r u i t f u l n e s s ( 6 , 12 , 1 6, 2 4 ,4 4 , 5 5, 8 7 ).

A m e a n o f 1 0 h s u n s h i n e p e r d a y d u r i n g i n f l o r e s c e n c e

f o r m a t i o n i s n e e d e d f o r a n a c c e p t a b l e l e v e l o f f e r t i l i t y

i n S u l t a n a v i n e s ( 1 6 ) . S h a d i n g f o r f o u r w e e k s d u r i n g

l a t e s p r i n g r e d u c e d t h e f r u i t f u l n e s s o f l a t e n t b u d s t o a

g r e a t e r e x t e n t t h a n s h a d i n g t r e a t m e n t s a p p li e d e a rl i e r

o r l a t e r d u r i n g t h e s e a s o n . I n N e w Z e a l a n d , s h o o t s

c o v e r e d w i t h H e s i a n s h a d e s ( 26 f u ll s u n l i g h t ) d u r i n g

D e c e m b e r t o M a y ( s u m m e r a n d a u t u m n ) p r o d u c e d

f e w e r b u n c h e s t h a n u n s h a d e d s h o o ts ( 55 ). H o w e v e r ,

g r o w t h c a b i n e t s t u d i e s s h o w e d t h a t i l l u m i n a t i o n

e q u i v a l e n t t o o ne q u a r t e r o f f u ll s u n l i g h t ( 39 k lx ) i s

s u f f i c ie n t to o b t a i n m a x i m u m f r u i t f u l n e s s i n

c o n t a i n e r - g r o w n p l a n t s o f M u s c a t o f A l e x a n d r i a ( 33 ).

I n v i n e s g r o w n i n c o nt r o ll e d e n v i r o n m e n t s , t h e n u m b e r

a n d s iz e o f i n f l or e s c e n c e p r i m o r d i a i n c r e a s e s w i t h i n -

c r e a s e i n l i g h t i n t e n s i t y (2 8 ) .

V e r t i c a l l y - t r a i n e d s h o o t s a r e m o r e f r u i t f u l t h a n

h o r i z o n t a l l y - t r a i n e d s h o o t s (2 9 ,8 6 ) . D i r e c t e x p o s u re o f

l a t e n t b u d s t o h i g h i n t e n s i t y l i g h t i m p r o v e s t h e f r u i t -

fu l n e s s o f b u d s b u t n o e f f e c t s o f t h e q u a l i t y o f l i g h t o n



9/17

FLOWERING IN GRAPEVINE 5 5

i n f l o r e s c e n c e f o r m a t i o n h a v e b e e n d e t e c t e d ( 8 5 ) .

I t i s o f t e n o b s e r v e d t h a t b u d s s i t u a t e d i n s i d e t h e

c a n o p y o f f i e l d - g r o w n v i n e s a r e l e ss f r u i t f u l t h a n t h o s e

a t t h e e x t e r i o r w h e r e b u d s a r e m o r e s t r o n g l y i l l u m i -

n a t e d (9 0) . T h e u s e o f t r e l l i s e s a n d s p l i t c a n o p i e s , a s i n

t h e G e n e v a D o u b l e C u r t a i n s y s t e m o f t r a i n i n g , g i v e s

i m p r o v e d f r u i t f u l n e s s o f b u d s a n d a n o v e r a l l i n c r e a s e

i n p ro d u c t i v i t y o f 5 0 t o 9 0% (9 0 ,12 9 ) .

A s w i t h t h e e f f e c t o f t e m p e r a t u r e , r e s p o n s e s o f

v i n e s t o d i f f e r i n g l i g h t i n t e n s i t i e s v a r y w i t h t h e c u l -

t i v a r . S u l t a n a , O h a n e z , a n d S h i r a z w e r e f r u i t f u l o n ly

a t l i g h t in t e n s i t i e s h i g h e r t h a n 1 9. 5 k l x b u t M u s c a t o f

A l e x a n d r i a a n d R h i n e R i e s l i n g w e r e f r u i tf u l w i t h a n

i l l u m i n a t i o n o f 1 9 .5 k l x (3 2 ).

P h o t o p e r i o d : P h o t o p e r i o d d o es n o t a f f e ct i n f lo r e s -

c e n c e i n d u c t i o n i n g r a p e s (3 ,4 ,6 ,7 ) , b u t t h e r e i s e v i -

d e n c e i n s o m e c u l t i v a r s t h a t t h e n u m b e r s o f i n fl o r es -

c e nc e p r i m o r d i a p e r b u d a r e g r e a t e r u n d e r l o n g d a y s

t h a n w i t h s h o r t d a y s ( 2 9 , 3 3 ) .

T h e f r u i t f u l n e s s o f v i n e s g r o w n i n g r o w t h c a b i n e t s

w a s p r o m o t e d b y i n c r e a s i n g t h e t i m e o f e x p o s u r e t o

h i g h i n t e n s i t y l i g h t ( 3 6 0 0 f t - C ) . T h e s e r e s u l t s c o u l d

n o t b e e x p l a i n e d b y t h e i n c r e a s e i n q u a n t i t y o f l i g h t f o r

u s e i n p h o t o s y n t h e s i s ( 33 ). I f t h e h i g h l i g h t i n t e n s i t y

w a s s u p p l i e d f o r m o r e t h a n 1 2 h o u r s p e r d a y , t h e f o r -

m a t i o n o f i n f l o r es c e n c e p r i m o r d i a a p p e a r e d t o d e p e n d

o n th e h o u r s o f i l l u m i n a t i o n r a t h e r t h a n o n t o t a l i nc i-

d e n t e n e r g y ( 3 3) . I n c o n t r a s t , t h e a c c u m u l a t i o n o f d r y

m a t t e r w a s r e l a t e d t o t ot a l i n c i d e n t l ig h t e n e r g y a n d

n o t t o t h e n u m b e r o f h o u r s o f i l l u m i n a t i o n ( 27 ). T h e r e -

f o r e , t h e m e c h a n i s m l e a d i n g t o i n f l o r e s c e n c e p r i m o r -

d i u m f o r m a t i o n i s n o t c l o s e l y r e l a t e d t o t h e m e c h a n i s m

o f d r y w e i g h t a c c u m u l a t i o n ( i. e. , p h o t o s y n t h e s i s ) d e -

s p i t e i t s r e q u i r e m e n t s f o r h i g h e n e r g y l i g h t .

A m e r i c a n s p e c i e s , i n c l u d i n g

V i t i s l a b r u s c a ,

a r e

m o r e s e n s i t i v e t o d a y l e n g t h t h a n V i t i s v i n i f e r a L .

( 7 0 ,7 1 ,1 6 2 ). D e l a w a r e v i n e s

Vi t i s v in i fera x V i t i s lab -

r u s c a )

g r o w n i n l o n g d a y s f o r m e d n e a r l y t h r e e t i m e s a s

m a n y i n f l o r e s c e n c e s a s t h o s e g r o w n i n s h o r t d a y s i r r e -

s p e c t i v e of t h e t e m p e r a t u r e r e g i m e . T h e f e r t i l i t y o f

M u s c a t o f A l e x a n d r i a w a s a f f e ct e d by t e m p e r a t u r e

r a t h e r t h a n b y d a y l e n g t h ( 3 2 , 1 6 2 ) .

T o s u m u p t h e i n f lu e n c e o f t e m p e r a t u r e a n d l i g h t

o n f r u i t f u l n e s s , B u t t r o s e ( 3 3 ) c o n s i d e r s t h a t t e m p e r a -

t u r e i s a d o m i n a n t f a c t o r f o r i n f l o r e s c e n c e p r i m o r d i a

f o r m a t i o n , b u t a c c o r d i n g t o R i v e s ( 1 2 4 ) l i g h t i n t e n s i t y

i s t h e l i m i t i n g f a c t o r . H o w e v e r , i t a p p e a r s t h a t a c o m -

b i n a t i o n o f e x p o s u r e to h i g h t e m p e r a t u r e a n d h i g h

l i g h t i n t e n s i t y i s n e c e s s a r y f o r m a x i m u m f r u i t f u l n e s s

o f l a t e n t b u d s .

W a t e r s t r e s s : P e r s i s t e n t w a t e r s t r e s s d e p r e s se s th e

f r u i t f u l n e s s o f l a t e n t b u d s ( 1 81 ) , a fa c t w h i c h e x p l a i n s

w h y r a i n f e d v i n e s u s u a l l y b e a r f e w e r f r u i t f u l b u d s

t h a n i r r i g a t e d v i n e s ( 58 ). S o il m o i s t u r e i s o d e o f t h e

c h i e f f a c t o r s i n f l u e n c i n g i n f l o r e s c e n c e d e v e l o p m e n t i n

g r a p e s ( 9 ) , a n d s t u d i e s w i t h v i n e s g r o w n i n c o n t r o l l e d

e n v i r o n m e n t h a v e s h o w n t h a t t h e n u m b e r a n d s i z e o f

i n f l o r e s c e n c e p r i m o r d i a a r e r e d u c e d b y w a t e r s t r e s s

( 3 4 ) . H o w e v e r , t h e r e a r e a l s o r e p o r t s t h a t w a t e r s t r e s s

i n c r e a s e s t h e f r u i t f u l n e s s o f b u d s ( 1 42 ). M a y ( 85 )

s u g g e s t s t h a t t h e r e d u c e d f o l i a g e d e n s i t y o f w a t e r -

s t r e s s e d v i n e s i m p r o v e s t h e i l l u m i n a t i o n w i t h i n t h e

c a n o p y a n d r e s u l t s i n i m p r o v e d f e r t i l i ty o f b a s a l b u d s ,

a f a c t o r w h i c h l e a d s t o i n c r e a s e d f r u i t f u l n e s s o f t h e

v i n e a s a wh o l e .

V i n e g r o w t h i s s e n s i t i v e t o w a t e r s t r e s s ( 1 7 0 ) a n d

t h e r e i s a r e d u c t i o n i n b o t h b u d f r u i t f u l n e s s a n d d r y

w e i g h t o f s h o o ts ( 3 4) . T h i s s u g g e s t s t h a t w a t e r s t r e s s

m a y a f f e c t f r u i t f u l n e s s i n d i r e c t l y t h r o u g h a d e c l i n e in

p h o t o s y n t h e s i s ( 8 2 ) . M o r e o v e r , w a t e r s t r e s s c a u s e s a

d e c r e a s e i n c y t o k i n i n i n x y l e m s a p ( 79 ) a n d a n i n c r e a s e

i n t h e a b s c i s i c a c i d l e v e l s i n l e a v e s a n d s t e m s (4 7 ,8 2 ) .

T h e i m p o r t a n c e o f c y t o k i n i n i n g r a p e f l o w e r i n g i s w e l l

e s t a b l i s h e d a n d w i l l b e d i s c u s s e d l a t e r i n t h i s r e v i e w .

T h e p a u c i t y o f i n f o r m a t i o n o n t h e r e l a t i o n s h i p b e -

t w e e n w a t e r s t r e s s a n d f r u i t f u l n e s s o f l a t e n t b u d s i s

d u e p r i m a r i l y t o t h e d i f f ic u l t y o f s e p a r a t i n g t h e s p ec i fi c

e f f ec t s o f w a t e r s t r e s s f r o m th o s e o f t e m p e r a t u r e a n d

l i g h t i n t e n s i t y .

M i n e r a l n u t r i t i o n : M o s t s t u d ie s on t h e m i n e r a l

n u t r i t i o n o f g r a p e s h a v e b e e n c o n c e rn e d w i t h b e r r y

d e v e l o p m e n t a n d w i n e q u a l i t y , a n d t h e r e a r e f e w r e -

p o r t s o n t h e e f f ec t s o f m i n e r a l n u t r i t i o n o n f lo w e r f or -

m a t i o n .

A n a d e q u a t e s u p p l y o f n i t r o g e n i s n e c e s s a r y f o r i n-

f l o r es c e n c e p r i m o r d i u m f o r m a t i o n a n d f o r th e d i f f er -

e n t i a t i o n o f f l o we r s (7 ). S iz e o f i n f l o r e s c e n c e p r i m o rd i a

i s g e n e r a l l y l i t tl e a f f e c t e d b y N n u t r i t i o n ( 15 9 ), b u t a n

i n c r e a s e i n t h e n u m b e r o f i n f l o re s c e n c e p r i m o r d i a f ol -

l o w i n g N a p p l i c a t i o n i s f o u n d w h e n t h e i n i t i a l N s t a t u s

o f t h e v i n e i s lo w (17 ) . Ho w e v e r , u n d e r s p e c i a l c i r c u m -

s t a n c e s , a p p l i c a t i o n o f n i t r o g e n c a n r e s u l t i n a r e d u c -

t i o n i n f r u i tf u l n e s s . A s u r v e y o f t h e p e t i o l e n u t r i e n t

s t a t u s i n 3 0 t r o p i c a l v i n e y a r d s s h o w e d a s i g n i f i c a n t

n e g a t i v e c o r r e l a t i o n ( r = - 0 . 9 4 6 ) b e t w e e n p e t io l e - N

a n d f r u i t f u l n e s s ( 1 0 0 ) . T h e r e i s a l s o e v i d e n c e t h a t t h e

N r e s e r v e s o f t h e c a n e a r e p r e f e r e n t i a l l y u t i l i z e d f or

t h e g r o w t h o f t h e s h o o t r a t h e r t h a n a d d e d n i t r o g e n ,

e v e n wh e n e x c e s s N f e r t i l i z e r i s s u p p l i e d (1 1 1 ) . T h i s

c o u l d e x p l a i n w h y s o i l a p p l i e d n i t r o g e n s e l d o m h a s a n

e f fe c t o n in f l o r e sc e n c e p r i m o r d i u m f o r m a t i o n i n

g r a p e s .

O p t i m u m p h o s p h o r u s ( P) n u t r i t io n p r o m o t e d bu d

f r u i t f u l n e s s b y i n c r e a s i n g t h e v i n e v i g o r ( 6 8 ) , a n d

p h o s p h a t e d e f i c i e n c y i s d e t r i m e n t a l t o i n f l o r e s c e n c e

f o r m a t i o n ( 60 ). L ow N , h i g h P a n d w a t e r s t r e s s a r e t h e

f a c t o r s a s s o c i a t e d w i t h h i g h f e r t i l i t y i n S u l t a n a v i n e s

(1 7 ) . Un d e r t r o p i c a l c o n d i t i o n s , p e t i o l e P c o n t e n t i s

p o s i t i v e l y c o r r e l a t e d w i t h t h e y i e l d o f g r a p e s (1 0 0) .

S t u d i e s w i t h r a d i o a c t i v e P i n d i c a t e d a p r e f e r e n t i a l a c -

c u m u l a t i o n o f P i n a c t i v e l y g r o w i n g s h o o t ti p s a n d i n

y o u n g b u d s w h i c h s u b s e q u e n t l y b e c a m e f r u i t f u l

( 5 3 , 7 2 , 1 2 3 ) . P i s p r e s e n t i n x y l e m s a p i n m i n e r a l f o r m

a t th e b e g i n n i n g o f t h e s o -c a l le d b l e e d i n g p e r i o d b u t

i t i s m o s t l y i n a n o rg a n i c fo rm d u r i n g f l o we r d i f f e r -

e n t i a t i o n a n d b u d b u r s t ( 6 7 ) .

T h e r e h a v e b e e n s e v e r a l s u g g e s t i o n s f o r a r o l e f o r

p o t a s s i u m ( K ) i n i n f l o r e s c e n c e f o r m a t i o n i n t h e

g r a p e v i n e ( 1 4 5 ,1 5 6 ). S o il a p p l i c a t i o n o f K i n K - d e -

f i c ie n t v i n e y a r d s i n M i c h i g a n a n d i n th e N i a g a r a

P e n i n s u l a c a u s e d a m a r k e d i n c r e a se i n t h e f r u it f u l n e ss



10/17

56 FLOWERING IN GRAPEVINE

of lat ent buds of Concord (75). Sim ila r effects of

K-nutrition were found in Sultana vines in California

(41). Potassium application increased the fruitfulness

and yield by 45% in the f irst year and 156% in the

second year. This large increase in yield may have

been related to the larger size of inflorescence primor-

dia which are produced by latent buds of K-fertilized

vines (159). Potassium is implicated in enzyme activa-

tion and carbohydrate mobilization in grapes (21). The

positive response of vines to potassi um ma y be related

to the fact that grapevines utilize the soil-applied K for

growth and bud development rather than the K stored

in the cane (111).

The growing of vine seedlings in mineral nutr ient

solutions induces precocious flowering (59,125,171)

and hydroponic culture forms part of a breeding strat-

egy for the g rape vine proposed by Bouquet (22). Op-

tim um levels of N, P and K are associated w ith

maximum cytokinin production by grape roots (65).

P H Y T O H O R M O N E S N D F L O W E R I N G

External factors are thought to exert their influ-

ence on flowering by modifying the internal chemical

makeup of the plant, particularl y t he balance of en-

dogenous hormones (161). Proof of this supposition re-

quires estab lishment of the necessary relationship be-

tween levels of endogenous hormones and the flower-

ing response. Information on endogenous hormones in

relation to flowering is especially difficult to obtain in

the grapevine. The organs of interes t, the Anl agen, are

very small and inaccessible, and the extraction and

estimation of auxins, gibberellins and cytokinins from

latent buds presents many technical problems. There-

fore, most conclusions on the role of phytohor mones in

flowering in grapes have been based on inferences from

the effects of exogenous hormones and gr owth reg-

ulators.

Gibberellins: Gibberellins are the only chemicals

known, so far, that are capable of inducing flower for-

mat ion in numerous p lan ts under s t r ic t ly non-

inductive conditions (185). Howev er, gibberellins are

inhibit ory to flower formation in the gra pevine (5), and

other fruit trees (62). Endogenous gibberellins have

been dete cted in xylem sap of grap evin es (101,109,134)

and te nta tivel y ident ified as GAI, GA3, GAs and GA9

(51,134). Lilov and Christov (77) found no close rela-

tionship between endogenous gibberellin levels and

grape flower formation. Nevertheless, grapevines are

very sensitive to exogenous gibberellins (143,173,176).

Appl icat ion of GA3 or GA4 + 7 at con cen trati ons as low

as 3 t~mol/L induced bur stin g of late nt buds in t he cur-

ren t season and inhi bited the fo rmation of inflores-

cence from Anlagen (150). However, gibberellins seem

to favor initi ation of Anlag en (150). In GA3-treated

plants Anlagen were formed precociously at normal

node positions and at nodes more proximally situated

than is normal (146). These GA-induced Anlagen did

not develop into inflorescences but gave rise to tendri ls

(150).

Grape tendrils usually contain a higher gibberellin

content t han other or gans (92). The elongation of ten-

drils results from the activity of a subapical meris tem

(167), and applications of gibberellin, a stim ulat or of

subapical meristem activity, greatly promote the

growt h of tendr ils (146,173). Exogenous gibberell in

also brings about the transformation of inflorescences

into tendrils or tendril-like structures (92,98).

Gr owt h r eta rd ant s: Complete or partial cessation

of vegetative growth favors flower initiation in many

orchard species (62). Accordingly, chlormequat, a

growth retardant, was used by several workers to re-

duce the vegetative growth and to induce flowering in

grapes (42,49,81,117,164,172,174). Besides promoting

inflorescence primordium formation in latent buds,

chlo rme quat induced ~'secondary inflorescences by

transform ing the tendrils of the prim ary shoot and lat-

eral shoots into inflorescences (42,78,150,163). Pinch-

ing and chlormequat treatment had additive effects in

promoting the flowering of lateral shoots of Muscat of

Alexandria (169).

The promotive effect of chlor mequat on flowering in

grapes was attributed by some workers to early shoot

maturation (73,83,113). Chlormequat not only retards

vegetative growth and induces flowering but also in-

creases fru it-set and chlorophyll content of leaves (43).

The wide spectr um of effects caused by chlormeq uat led

Coombe (43) to suggest that this chemical could induce

~Tar-reaching alter atio ns in cell metabolism in the

grapevine.

Anlagen formation and tendril elongation are inhi-

bited by chlormequ at (150), an inhibi tor of gibberellin

biosynthesis (74). Chlormequat induced the formation

of inflorescences in place of tendrils (150), a response

which may be rel ated to effects of this growth re tar-

dant on cytokinin synthesis (135). It is probable that

chlor mequat exerts a dual role in the control of flower-

ing in grapes, viz., inhibiti on of gibberell in biosyn-

thesis an d the elevati on of cytokini n levels. Validation

of this hypot hesis aw aits t he av ailabi lity of precise in-

formation on changes in the endogenous levels of

cytokinins and gibberellins in response to chlormequat

treatment.

Applications of chlormequat stimulat e biosynthesis

of cyto kinins not only in grapes (135,136,139) but also

in Vicia faba (48) and in apical buds of henopodium

rubrum during floral induction (165). Chlormequat in-

duced swel ling of roots (136) and doubled the vo lume of

bleeding sap (xylem sap) of grap evin es (107). Besides

an increase in total cyto kinin conten t of xylem sap

(176) and leaves (11), an unusual cytokinin was also

found in xylem sap of chlor mequa t-tr eated vines (107).

Chlor mequa t did not induce precocious flowering in

grape seedlings, but mi xtur es of the cytoki nin, PBA,

and chlormequat induced precocious flowering and

fruiting in Muscat Hamburg seedlings (153). Another

growth retarda nt, Amo-1618 [ Ammon ium (5-hydroxy:

carvacryl) trimethyl chloride piperidine carboxylate]

also induced precocious flowering in Muscat Hamburg

seedlings when applied with PBA (153).

Daminozide and the growth inhibitors, maleic hy-

drazide, ethephon and morphactin, do not promote

flowering in the grapevine in vivo (172,174) or in vitro

(146).



11/17

F L O W E R I N G I N G R A P E V I N E m 7

C y t o k i n i n s :

The role of cytokini n in t he control of

flowering in plants is not well understood and only a

few species have been made to flower by treatment

with exogenous cytokinin (185). Zeatin, zeatin

riboside, and zeat in ribotide are found in the xylem sap

of grapevines before bud burst and dur ing th e period of

active shoot growth (80,110,137,138,140). Root apices

are a major source of cytokinins in plan ts (139), but the

relationship between cytokinin and flowering in

grapes has only recently been the subject of investiga-

tion.

From st udies of bud anat omy by scanning electron

microscopy, it is now clear that Anlagen which

undergo extensive bra nchi ng give rise to inflorescences

and that Anlagen which produce only two or three

branches grow into tendrils (149). It follows that the

control of inflorescence formation in grapes hinges

upon the control of bran chin g of Anlag en or thei r de-

rivatives, the tendrils. Isolated tendrils were induced

to branch profusely and they grew into inflorescences

when cultured

i n v i t r o

with benzyladenine (BA),

6- (ben zy 1 mi no )- 9-( 2- t et r ah y dro py r an y 1 - 9 H- purl ne

(PBA) or zeatin riboside (148). In intact vines, and in

partially defoliated vines, repeated applications of

PBA to shoot apices, caused inflorescences to be formed

in place of tendri ls and t his effect of cytokin in was

found in 12 cultivars of V i t i s v i n i f e r a in six other V i t i s

species, and in

M u s c a d i n i a r o t u n d i f o l i a

(149,154).

Moreover, these cytokinin-induced inflorescences pro-

duced ripe fruits which contained viable seeds. Ten-

drils of cytokinin-treated plants were transformed into

inflorescences regardles s of the sex of the vine - - male,

female or hermaphrodite (154). Male vines were more

susceptible to cytokinin-directed conversion of tendrils

into inflorescences than female m or hermaphrodite

vines. Mixtu res of cytokini n (BA) and chlor mequat in-

duced inflorescence formation in vines grown under

non-inductive temperatures (18C to 21C) (150).

The ability of cytokini n to tran sfor m tendri ls into

inflorescences is not restricted to cultivars but is found

also in seedlings. Repeated t rea tm ent of shoot apices

and young tendrils of grape seedlings with cyt okinins

(PBA or BA), induced the first-formed tendrils to ini-

tiate flowers wit hin four weeks of germin ation. Seed-

lings of Cabernet S auvignon and Muscat Hamb urg

were induced to flower and to develop bunches of

grapes with viable seeds with cytokinin (PBA) within

eight months of germination (153).

The differentiation of grape flowers from inflores-

cence primordia is also a cytokinin-requiring process

(97,98,116) and there is evidence that cytokinins pro-

duced in roots are involved in flower development. In-

florescence primordia in lat ent buds of hardwood cut-

tings fail to develop and atr ophy if bud burst precedes

the emergence of adventitious roots but normal in-

florescences are retained when cuttings are made to

form roots in adv ance of bud bur st (95). In rootless

cuttings exogenous cytokinins are needed for normal

development of inflorescences. Grape leaves are strong

sinks for root-produced cytokinin (54). In cuttings, re-

moval at bud burst of the young l eaves formed basal to

the inflorescence seems to enhance t he si nk-capacity of

inflorescence for cytokinin and inflorescences develop

in normal manner (97).

Exogenous cytokinins (PBA, BA, zeatin and dihy-

drozeatin) induced pistil development in male vines of

several Vitis species and interspecific hybrids

(46,50,52,93,102,103,104,105). Cytokini ns are thou ght

to promote pistil development in male vines by coun-

teracting the effects of a postulated inhibitor (104).

Cytokini ns are impli cated in the control of man y

aspects of grape reproduction including inflorescence

form atio n (148,149,150,153); diffe rent iat ion of flowers

(97,98); pistil development (102); fruitset (178); fruit

development (175) and somatic embryogenesis in un-

fertilized ovules

in vi tro

(99,152). These findings, to-

gether w ith the knowledge of high cytokini n activity in

xylem sap during bud burst and flowering and high

cytokinin activity in fruits (38,110), strongly suggest

that endogenous cytokinin is a primary regulator of

reproductive growth in the grapevine.

The mechanism by which cytokinins control flower

formation is unknown. Cytokinin is regarded as a

mitotic component of the floral stimulus in S i n a p i s

a l b a

(20) and was also shown to be involved in photo-

periodic induction in P h a r b i t i s n i l by promoting the

transl ocation of the floral stim ulus (112). Cytokinins

increase the permea bilit y of cell mem bran es (130,168),

and exogenous cytokinins are strong mobilizers of

photosynthates in grapes (131,132,177). Sachs and

Hackett (126) have provided evidence that flower for-

mation in Bougainvillea is related to the gibberellin:

cytokinin balance and that these hormones control

flowering by affecting the di stribu tion of metabolites.

It needs to be stressed, however, that the relationship

of the various biochemical functions of cytokinins to

cytokinin-directed flower formation is not yet clear.

Othe r classes of plant h ormones are also known to

promote mitosis, membrane permeability and the dis-

trib utio n of metabolites, but the compounds concerned

have n ot been closely linked with t he control of flower-

ing.

D E V E L O P M E N T A L P A T H W A Y S O F T H E

G R A P E V I N E A N L A G E

As will be clear from the foregoing sections of this

review, the Anlagen and tendril primordia (branched

Anlagen) possess a remarkable morphogenetic plastic-

ity. Tendril primordia and tendrils give rise to inflores-

cences when treated with cytokinin (148,149,150,153)

and inflorescences are converted into tendrils or

tendril-like organs by gibberellin (92,98). In addition,

inflorescences have been induced to form from tendr ils

with cytokinin treatment both

in v i t ro

(96) and

in vivo.

Alth ough Anlag en n ormal ly give rise eit her to in -~

florescences or to tendrils, they may also be made to

grow into shoots. Exposure to low temperatures ( 1 mM) of exogen-

ous cytokinins and/or chlormequat caused several

A n



12/17

5 8 m F L O W E R I N G IN G R APEV I N E

lagen to form shoots, both in cultivars and in seedlings

(150,155). Excised tendrils grew into inflorescences

when cultured n v tro with PBA or BA (5-10 t~mol/L),

but if these tendril-derived inflorescences were treated

subsequentl y with a high concent ration of PBA (> 20

t~mol/L) they, too, grew into shoots (146).

The available information on the developmental

path ways of Anla gen have been combined and pre-

sented in diagrammatic form (Fig. 5). For purposes of

description, Anlagen which have produced a bract and

two branches (inner arm and outer arm) are referred to

as tendril primordia (Fig. 3, Stage 4).

[ I

V E G E T T I V E P E X

I

ENDRIL

oO PRIM ORD IUM

oO . . [

[ s . o o

l

i n v i v o i n v i t r o

~ , ,O N , V i n v i t r o

ON,V in v i vo

Fig. 5. Developmental pathways of the Anlage.

T H E P H Y S I O L O G I C A L B A S I S O F F L O W E R

F O R M A T I O N I N T H E G R A P E V I N E

Flowering in plants is believed by many workers to

be induced by a single substance, '~florigen (180,185),

but others have suggested that the floral stimulus con-

sists of two comp lementary com ponent s (37,39). Ac-

cording to Thimann (166), flowering is merely a devel-

opmental process under t he control of the in terpl ay of

hormones, and Zeevaart (184) has proposed that the

req uir eme nt for a specific balance of hormo nes for

flower formation is more readily applicable to woody

perennials than to herbaceous annual plants.

In su mmar izi ng 40 years of research on the ~'hor-

mona l concept of flowering Ch ail akh yan (39) con-

cluded that the main function of gibberellins is to con-

trol the f ormatio n and grow th of floral stems or in-

florescence axes. The responses of grape vines to

exogenous gibberellins and chlormequat are consistent

with this view. Gibberellins are involved in the initia-

tion of Anlagen (formation of inflorescence axes) and

are necessary for the growth of inflorescence axes, i.e.,

the extension growth of the two-br anched Anlagen

(Stage 4).

According to Carr (37) two different inductive

stimuli could be involved in the flowering of plants.

One is the ~'primary induction which is %ontagiousl y

propagated and the other is a ~secondary induction

which occurs locally. Initia tion of Anla gen an d tendri l

formation could be regarded as the ~primary induc-

tion , a condition which is permanent in grape cul-

tivars which are perpetuated by vegetative propaga-

tion. The secondary stimulus , which is requir ed an-

nuall y for the direction of Anla gen into the pat hway of

inflorescence development, is probably cytokinin.

In nature, grapevines produce numerous Anlagen

but most grow into tendrils and only a few Anlagen

give rise to inflorescences. This suggests that gibberel-

lin is readily available for initiatio n of Anlag en and for

elongation of tendri ls and t hat inflorescence formation

is normally limited by the cytokinin supply (149,154).

The finding that repeated applications of cytokinin are

requir ed for trans form atio n of tendri ls into inflores-

cences suggests th at a continuous inf lux of endogenous

cytokinins into Anlagen is needed for flower formation

in the grapevine. A hypothetical scheme for the hor-

monal control of Anlage, t endril and inflorescence for-

mation in the grapevine is presented in Fig. 6. The

postulated inhibitors in this scheme are endogenous

compounds which mimic the effects of the synthet ic

growth ret ard ant , chl ormequat, i.e., inhibition of gib-

berell in bi osynthesis and promotion of cytokinin

biosynthesis.

v e g e t a t i v e a p e x [

A n l a g e n

T e n d r i l s

G I B B E R E L L I N S

C Y T O K I N I N

[ I n f l o r e s c e n c e s

INCRE SE INHIBIT PROMO TE

F ig . 6 . A hy pothe t ica l sche me fo r t he hormo na l con t ro l o f An lage ,

tendr i l and inf lorescence format ion in the grapevine Vit is v in i fera L.).



13/17

FLOWE RING IN GRAPEV INE m 9

C O N C L U S I O N

T h e e x t e r n a l f a c t o r s w h i c h p r o m o t e f l o w e r i n g i n

g r a p e s , s u c h a s s h o r t t e r m e x p o s u r e t o h i g h t e m p e r a -

t u r e , h i g h l i g h t i n t e n s i t y a n d o p t i m u m l e v e l s o f s o i l

m o i s t u r e a n d m a c r o n u t r i e n t s , a r e a l s o f a c t o r s w h i c h

p r o m o t e c y t o k i n i n b i o s y n t h e s i s i n p l a n t s ( 1 4 , 6 5 , 9 1 ,

1 4 1 , 1 7 9 , 1 8 3 ) . C o n v e r s e l y , f a c t o r s w h i c h d e p r e s s f l o w e r

f o r m a t i o n , s u c h a s l o w l i g h t i n t e n s i t y , l o w t e m p e r a t u r e

a n d w a t e r s t r e s s , h a v e a n i n h i b i t o r y e f f e c t o n e n d o g e n -

o u s c y t o k i n i n p r o d u c t i o n ( 6 1 , 7 9 ). M o r e o v e r , e x o g e n o u s

c y t o k i n i n s p r o m o t e f l o w e r f o r m a t i o n i n g r a p e v i n e s

g r o w n a t n o n - i n d u c t i v e l o w t e m p e r a t u r e s , a n d p la n t s

g r o w n i n t h e d a r k ( 1 4 6 ). I t i s c l e a r t h a t c y t o k i n i n i s o f

c e n t r a l i m p o r t a n c e i n t h e c o n t r o l o f f l o w e r i n g i n t h e

g r a p e v i n e .

L I T E R A T U R E C I T E D

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E f f e c t o f m i n e r a l f e r t i l i z e r s o n n u c l e i c a c i d c o n t e n t i n v i n e s h o o t s .

A g r o k h i m i y a N o . 4 : 9 1 - 3 ( 1 9 7 6 ) .

2 . A g a o g l u , Y . S . A s t u d y o f t h e d i f f e r e n t i a t i o n a n d t h e

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7 . A l l e w e l d t , G . D i e B e e i n f l u s s i n g d e r E r t r a g s b i l d u n g b e i

R e b e n d u r c h T a g e s l ~ n g e u n d T e m p e r a t u r . K a l i - B r i e fe , F a c h g e b i e t

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8 . A l l e w e l d t , G . , a n d G . H . B a l k e m a . U b e r d i e A n l a g e v o n

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9 . A l l e w e l d t , G . , a n d W . H o f a c k e r . I n f l u e n c e o f e n v i r o n m e n -

t a l f a c t o r s o n b u d b u r s t f l o w e r i n g f e r t i l i t y a n d s h o o t g r o w t h o f

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1 1 . A n d a n o v a , T . A . , a n d D . T . L i l o v . C h a n g e s o f t h e f r e e

c y t o k i n i n s i n t h e s h o o t s a n d l e a v e s i n p l a n t d i f f e r i n g i n t h e i r

grow th . C .R . A c a d . Bulg . Sc i . 30 :905-8 (1977) .

1 2 . A n g y a n , F . , P. M . K o p c s a i , a n d D . P o l y a k . B u d t e s t i n g i n

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1 3. A n t c l i f f, A . J . , a n d W . J . W e b s t e r . S t u d i e s i n t h e S u l t a n a

v i n e . 1 . F r u i t b u d d i s t r i b u t i o n a n d b u d b u r s t w i t h r e f e r e n c e t o

f o r e c a s t i n g p o t e n t i a l c r o p . A u s t . J . A g r i c . R e s . 6 : 5 6 5 -8 8 ( 1 9 5 5) .

14 . A t k in , R . K . , G . E . Ba r ton , a nd D . K . Robin son . E f fe c t o f

r o o t - g r o w i n g t e m p e r a t u r e o n g r o w t h s u b s t a n c e s i n x y l e m e x u d a t e

o f Z e a m a y s . J . Exp . Bot . 79 :259-66 (1973) .

1 5 . B a l a s u b r a m a n y a m , V . R . , a n d S . D . K h a n d u j a . E f f e ct o f

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a n d p r o t e i n c o n t e n t o f l e a v e s a n d f r u i t i n g o f T h o m p s o n S e e d l es s

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t r o g e n a n d f r u i t f u l n e s s i n t h e S u l t a n a v i n e . A m . J . E n o l . V i t i c .

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t o g e t h e r w i t h a n a c c o u n t o f t h e d i f f e r e n t i a ti o n a n d d e v e l o p m e n t o f

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M . B o d s o n . C y t o k i n i n a s a p o s s i b le c o m p o n e n t o f t h e f l o r a l

s t i m u l u s i n

Sinapis a lba .

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2 1 . B o u a r d , J . I n f l u e n c e o f m a n u r i n g o n s o m e m o r p h o l o g i c a l

a n d b i o c h e m i c a l c h a r a c t e r i s t i c s o f c a n e s o f Vitis vinifera L . V a r i e t y

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d ~ f i n i ti o n d u n s c h e m a d e s ~ l e c t i o n a p p l i c a b l e a l a c r e a t i o n d e

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l e a v e s a n d t h e d e g r e e o f d i f f e r e n t i a t i o n o f w i n t e r b u d s i n

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g r a p e v i n e s . H o r t i c . A b s t r . 4 4 : 3 1 9 - 2 5 ( 1 9 7 4 ) .

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Physiology of Flowering in the Grapevine

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