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scion relations in horticultural crop physiology
Scientia Horticulturae, 2 ( 1 9 7 4 ) 2 2 1 - - 230. Elsevier Scientific P u b l i s h i n g C o m p a n y , A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s
ROOTSTOCK/SCION
RELATIONS
IN HORTICULTURAL
CROP
PHYSIOLOGY
F.R. T U B B S
John Innes Institute, Norwich (Great Britain) F o r m e r l y of East Malling R e s e a r c h S t a t i o n , M a i d s t o n e ( G r e a t B r i t a i n ) ( R e c e i v e d J a n u a r y 16, 1 9 7 4 )
ABSTRACT T u b b s , F.R., 1 9 7 4 . R o o t s t o c k / s c i o n r e l a t i o n s in h o r t i c u l t u r a l c r o p p h y s i o l o g y . Scientia Hort., 2: 2 2 1 - - 2 3 0 . A p r e l i m i n a r y r e p o r t is m a d e of t h e results o f g r o w t h studies o n c o m p o u n d t r e e s f o r m e d o f all c o m b i n a t i o n s , as scion a n d as r o o t s t o c k , o f t h r e e clones, c h o s e n t o cover a wide r a n g e o f vigour, o f apple, quince, a n d cherry. U n d e r t h e c o n d i t i o n s o f t h e o r c h a r d e x p e r i m e n t a n d w i t h t h e clones used, n o d i s t i n c t i o n was f o u n d b e t w e e n i n f l u e n c e o n t r e e size of a n y a p p l e c l o n e w h e n p r e s e n t as t h e scion or w h e n p r e s e n t as t h e r o o t s t o c k . Major d i s t i n c t i o n s in i n f l u e n c e as s c i o n or as r o o t s t o c k were, h o w e v e r , f o u n d in t h e case o f c e r t a i n q u i n c e a n d c h e r r y clones. E v i d e n c e as t o t h e p r e c o c i t y o f f l o w e r i n g of t h e scions o f c o m p o u n d t r e e s i n d i c a t e s t h a t p r e c o c i t y m a y o c c u r i n d e p e n d e n t l y o f a d w a r f i n g influence.
INTRODUCTION Scion/rootst0ck effects,'proven or reported by experienced horticulturalists, have been recorded among woody perennials over a very wide range of orders and families. The great range of rootstock/scion interaction in all aspects of growth and reproduction of the compound tree is well illustrated in pomological literature. A general survey of the whole field has recently been published by Tubbs (1973) as two review articles in Horticultural Abstracts, to which reference should be made for relevant citations. The early workers at East Mailing, vied with by Dutch and German horticulturalists and disputed by those in America who placed all emphasis on the importance of scion influence or of stem tissues, laid the foundations of further critical study of such effects. They enabled clear recognition of the problems posed by the major interactions they found between the characteristics of growth and fruiting of the scion on the one hand and the "vigour" of the rootstock on the other. Growth studies early indicated the need for explanation of the means whereby rootstock and scion mutually adjusted their growth such 'that, whether fruiting on the one hand, or non-fruiting on
222
the other, under given environmental and cultural conditions, the ratios of scion weight to rootstock weight were independent of the size of the tree resulting from t h a t mutual interaction. We are now entering the exciting stages when explanation can be sought through painstaking analysis of those hormonal relations adumbrating or controlling the seasonal and correlated activity of meristems together with the a m o u n t and ultimate distribution in tissue formation or energy reserves, in roots as in shoots, of the nett assimilate of the tree. The experiments now reported will, it is hoped, later provide unique material for further such analysis by those who are undertaking the basic studies in this field at East Malling. It was here that Vyvyan (1955) early recognised the need for critical growth studies as basic to the search for verifiable hypotheses as to the mechanisms of the striking mutual influences exerted by rootstock and scion. His experiments from 1927 onwards were later developed by Maggs (1962) on a longer term basis; these in turn have been succeeded by the meticulous and even longer term experimentation now being carried out by Barlow (1971), Dudney (1971), and Trowell (1972). Vyvyan's main approach was based on the then novel procedure of studying the growth of c o m p o u n d trees formed by the use, both as scions and as rootstocks, of clonal apples (rootstocks) in all combinations. Such experiments clearly required longer duration than the two years of Vyvyan's first experiment, as was recognised later. The studies of Trowell (1972) are entirely of the vegetative growth of deblossomed trees, the role of fruiting in the growth of root and shoot being now well d o c u m e n t e d (Barlow, 1971). It is to be noted, however, t h a t the emphasis in such studies had always been on apple with its established clones of k n o w n vigour, rather than on quince, plum or cherry. MATERIALS AND METHODS Experiments are in progress on all four species, apple, quince, plum, cherry, based on well replicated comparisons of three clones of each, in all their nine possible combinations. The tree-size data (October 1972) are from freely growing trees of three seasons' growth from working, deblossomed but unpruned save for the formation in the nursery year of a clean scion stem of at least 60 cm above the union. The apples were budded high (25 cm) in summer 1969, the quinces and cherries bench-grafted winter 1969/1970 on rooted stool or layer-bed shoots of one year's growth, as were the plums, to be reported later, in 1971/ 1972. The rootstock was thus a year (quince and cherry) or two years (apple) old when the scion started into growth. It is considered that the subsequent three seasons' growth was sufficient to allow of the c o m p o u n d trees reaching mutual adjustment between rootstock and scion over initial size and 'age' inequalities but not necessarily, of course, a final size relationship. The flowering records, taken in spring 1973, are in all cases the first flowering
223 save for one or two isolated blossoms on occasional trees of M9a/M9a in spring 1972 - - t o o few to justify inclusion. All clones, save M9a (carrying the three latent apple viruses only), were free of k n o w n viruses. The conclusions t o be drawn f r o m experiments of this t y p e are restricted t o evidence as to t h e behaviour of each clone: (1) as a scion above its own r oot s and also above the roots of, here, t he two o t h e r genotypes; (2) as a r o o t s t o c k , below its own scion and also below the scions of, here, the two o th er genotypes; (3) in interaction o f r o o t s t o c k and scion i.e. behaviour of particular rootstock/scion combinations departing f r om the consistency t o be e x p e c t e d f r o m (1) and (2). An efficient e x p e r i m e n t of this t y p e should thus include all combinations of genotypes selected as examples covering a wide range of vigour and o f potential p r eco city and fruitfulness. It m a y be recalled t hat among the apple ro o t s to ck s first studied b y V y v y a n was M4, which was included following Halton (1923) in order t o test (though w i t h o u t conclusive result) the then novel possibility that the r o o t and s hoot of the same clonal g e n o t y p e might differ in their intrinsic growth potential and t h e r e b y also in their growth controlling influence in t he m ut ual interaction of r o o t s t o c k and scion in the c o m p o u n d tree. However, it was n o t until 1950 t h a t the possibility received s u p p o r t f r o m the w or k of Sax (1950); Maggs (1957) r e p o r t e d striking experimental evidence from plums. T he experimental results comprise observations on vegetative growth and on first flowering T he f o r m e r ones, to be presented in Tables I--VI, were subjected to logarithmic t r a n s f o r m a t i o n and back-transformation according t o Pearce (1953). This is a statistical device making use of the fact t hat the distribution of data, o f t e n departing f r o m normal as to t r e a t m e n t effects in small samples, mo re nearly approaches normal when t ransform ed in this way. The data in Tables I--VI are f r o m back-transformation. EXPERIMENTAL RESULTS Vegetative g r o w th in apple
The apple e x p e r i m e n t consists o f the nine possible combinations o f three genotypes with ninefold replication, widely spaced in single tree plots. These were the dwarfing M9a; the m o d e r a t e l y dwarfing, after initial vigorous growth, M26; and the semi-vigorous MMlll. Table I shows the mean total length of all scion stems and branches achieved after three growing seasons o f the scion. It is immediately apparent t h a t n o t only are there distinct differences in vigour b etween th e three genotypes, but that these are of the same order w h e t h er as scion or as r o o t s t o c k . Main effects and differences are all significant, save t h a t as r o o t s t o c k s M26 is just n o t significantly different f r o m MMlll at this stage of growth of t he
224 TABLEI Total length (m) of scion extension growth in apple after three growing seasons October, 1972
R•
M9a M26 MMlll
M9a
M26
MMlll
4.0 9.3 9.1
8.4 13.4 18.2
8.7 20.1 25.2
Weighted means for each, as scion and as rootstock As scion 6.6 13.6 16.1 As rootstock 7.0 12.7 16.4 t r e e s . B e h a v i o u r o f i n d i v i d u a l c l o n e s as r o o t s t o c k a n d as s c i o n is v e r y similar. This c o n c l u s i o n is s u p p o r t e d b y t h e d a t a f o r h e i g h t of s c i o n a b o v e t h e u n i o n ( T a b l e II). Main effects of scion and r o o t s t o c k varieties are very highly significant and clear cut, there being no interaction specific to particular combinations. B e h a v i o u r as s c i o n o r as r o o t s t o c k is a g a i n similar. TABLE II Height of scion above union (m) in apple after three growing seasons October, 1972
M9a M26 MMlll
M9a
M26
MMlll
1.08 1.61 1.55
1.55 2.05 2.09
1.42 1.80 1.94
Weighted means for each, as scion and as rootstock As scion 1.39 1.88 1.71 As rootstock 1.34 1.81 1.84
We c a n c o n c l u d e , t h e r e f o r e , t h a t h e r e t h e r e is no e v i d e n c e of d i f f e r e n t i a l v i g o u r b e t w e e n tissues o f t h e s e t h r e e g e n o t y p e s (i.e. in t r e e s t h r e e y e a r s o l d a n d u n i n f l u e n c e d b y d i f f e r e n t i a l p r e c o c i t y o f f r u i t i n g ) w h e n p r e s e n t as s c i o n or as r o o t s t o c k r e s p e c t i v e l y in t h e c o m p o u n d t r e e . T h i s is n o t , of c o u r s e , evidence t h a t such differences w o u l d n o t occur with o t h e r clones t h a n these, o r u n d e r d i f f e r e n t c i r c u m s t a n c e s e.g. Mg ( V y v y a n , 1 9 5 5 ; Maggs, 1 9 6 2 ) .
225
Vegetative growth in quinces T u r n i n g t o quinces, all c o m b i n a t i o n s o f t h r e e clones w e r e used w i t h 18 f o l d r e p l i c a t i o n , w i d e l y spaced, in single t r e e plots. T h e s e were: Q u i n c e A, Q u i n c e C, and Q u i n c e C84, all virus free. R e f e r e n c e s t o t h e t w o f o r m e r a b o u n d in p o m o l o g i c a l literature; P a r r y ( 1 9 7 0 ) has s h o w n t h a t t h e d w a r f i n g e f f e c t , relative t o Q u i n c e A, o f Q u i n c e C w h e n use~d as a r o o t s t o c k f o r p e a r cultivars arises n o t so m u c h f r o m d i f f e r e n c e s in vigour i n f l u e n c e in t h e earlier years b u t r a t h e r f r o m t h e heavier and earlier c r o p p i n g o f t h e scion i n d u c e d b y Q u i n c e C as r o o t s t o c k . Q u i n c e C84 is an East Malling s e l e c t i o n , b y far t h e m o s t vigorous (in its e f f e c t o n t h e C o n f e r e n c e pear scions) o f all t h o s e studied. T h e b u s h y g r o w t h o f quinces p r e c l u d e d such detailed measurem e n t s a f t e r t h r e e growing seasons as f o r apple and cherry. D a t a are, h o w e v e r , available f o r t o t a l length o f t h e t h r e e longest laterals and f o r height o f scion a b o v e u n i o n a f t e r t h r e e growing seasons f r o m grafting. Table III s u m m a r i z e s t h e d a t a f o r t o t a l length. TABLE III Total length of three longest laterals (m) in quince after three growing seasons October, 1972
A C C84
A
C
C84
1.79 1.81 1.81
1.42 1.45 1.54
1.76 1.93 1.95
Weighted means for each, as scion and as rootstock As scion 1.81 1.47 1.88 As rootstock 1.65 1.72 1.76 T h e r e is n o i n t e r a c t i o n , i.e. n o e f f e c t specific to p a r t i c u l a r c o m b i n a t i o n s . T h e overall e f f e c t s o f scion, t o g e t h e r w i t h t h o s e o f r o o t s t o c k , are highly significant, P = 0.001 and P = 0.01, respectively. Clearly, t h e g e n o t y p e s behave q u i t e d i f f e r e n t l y in their t w o roles, Q u i n c e A being more vigorous as a scion t h a n as a r o o t s t o c k , Q u i n c e C being less vigorous in its i n f l u e n c e as a scion t h a n as a r o o t s t o c k (c.f. H a l t o n , 1 9 2 8 ) , and Q u i n c e C84 resembling t h e t h r e e apple g e n o t y p e s studie~l in t h e similarity o f its i n f l u e n c e in t h e t w o roles. This c o n c l u s i o n is strongly r e i n f o r c e d b y t h e d a t a f o r scion h e i g h t (Table IV). T h e b e h a v i o u r s o f differing c o m b i n a t i o n s are highly individual ( i n t e r a c t i o n P = 0.001). Again Q u i n c e A and Q u i n c e C e x e r t q u i t e d i f f e r e n t influences o n t h e c o m p o u n d tree, a c c o r d i n g as t o w h e t h e r t h e y are p r e s e n t as scion or as r o o t s t o c k . Q u i n c e C84 e x e r t s similar influences in b o t h roles.
226 TABLE IV H e i g h t o f s c i o n a b o v e u n i o n ( m ) in q u i n c e a f t e r t h r e e growing seasons O c t o b e r , 1 9 7 2
\-~Scion
Quince A
Quince C
Quince C84
1.67 1.70 1.78
1.34 1.28 1.32
1.51 1.76 1.61
Rootstock \`
Quince A Quince C Quince C84
W e i g h t e d m e a n s f o r each, as s c i o n a n d as r o o t s t o c k As scion 1.72 1.31 1.63 As rootstock 1.50 1.57 1.56
Again, these data provide no evidence t h a t some ot her three quince genotypes might n o t behave as did the three chosen apples. What t h e y do is to provide evidence of c o m p l e x i t y in r o o t s t o c k / s c i o n relations n o t previously apparent, i.e. the possible occurrence o f differential influence, as scion and as r o o t s t o c k , by a single g e n o t y p e of quince. Vegetative g r o w t h in cherry
The evidence obtained f r om the cherry experiment was even m o r e striking. The trees were planted in a widely spaced eightfold replication of the nine combinations o f three genotypes, with num e rous b o u n d a r y guards. Owing to bad weather conditions after planting, during the 1 9 6 9 / 1 9 7 0 winter, the original design was severely compromised. However, thereafter all surviving trees grew and developed normally and well. I am particularly indebted to Dr. Pearce and his staff of the Statistics Section of East Malling Research Station for their comprehensive study of all the data presented, but particularly for enabling the following summaries of the cherry growth to be drawn despite such initial difficulties. The three clones were the well-known East Malling F 1 2 / 1 , of m o d e r a t e vigour, and two recent selections, t he very dwarf Fb 2/58 (15) and the vigorous Fb 2/58 (48), now to be referred to as " 1 5 " and " 4 8 " , whose capabilities as r oot s t oc ks are as y e t largely u n e x p l o r e d The figures for F 1 2/ 1 on its o w n roots must be regarded as indicative only, owing t o low replication of this one combination. Data are available for t he total length of scion growth produced in three scion growing seasons and for height of scion above union by the same date, O c t ob er 1972. Table V presents the data for total length. The overall significance of t he differences shown is again high (P = 0.001). There are clear overall differences between scions, while in root st ocks it is F 1 2 / 1 that stands out as the m or e dwarfing. The outstanding contrast is b e t ween the respective influences o f " 1 5 " as scion and as r o o t s t o c k . The sheer magnitude o f this difference is very striking; in F12/1 and " 4 8 " the same effect is observable, though to lesser e x t e n t and of opposite sign.
227 TABLE V Total length (m) of scion growth in cherry after three growing seasons October, 1972 ~Scion
F12/1
"15
48"
Rootstoc~-F12/1 "15" "48"
6.3 12.6 12.6
2.1 6.2 5.8
19.5 35.5 35.5
Weighted means for each, as scion and as rootstock As scion 10.0 4.2 29.0 As rootstock 6.4 14.0 13.7 Arithmetic means for each, as scion and as rootstock As scion 10.5 ' 4.7 30.2 As rootstock 9.3 18.2 18.0 T h e r e is c l e a r e v i d e n c e h e r e , n o t a l o n e o f b o t h s c i o n a n d r o o t s t o c k d i f f e r ences and of that individuality of each combination of pairs of genotypes to which we are accustomed, but also both that a dwarf clone may possess a p o t e n t i a l l y v i g o r o u s r o o t s y s t e m as i n " 1 5 " a n d a l s o t h e r e v e r s e , as in " 4 8 " . The highly significant effects for height of scions in Table VI are here associated with scion differences, rootstock differences being insignificant. Again both F12/1 and "15" exert markedly different influences in the comp o u n d t r e e as s c i o n a n d as r o o t s t o c k : o t h e r d a t a i n d i c a t e t h a t t h e c o n t r a s t o f r o o t s t o c k e f f e c t s s h o w n b y T a b l e s V a n d V I m a y a r i s e in p a r t f r o m t h e relatively small number of extension shoots and greater mean length on scions over F12/1 and, with "15" (over F12/1 especially) their relatively very small length. TABLE VI Weight of sciona ~ b ~ v e union (m) in cherry after three growing seasons October, 1972 ion
F12/1\ "'-
"15 . . . .
2.23 2.63 2.57
0.89 1.05 1.07
48"
Rootstock~ F12/1 "15" "48"
2.00 1.99 2.14
Weighted means for each, as scion and as rootstock As scion 2.47 1.00 2.08 As rootstock 1.58 1.79 1.81 Arithmetic means for each, as scion and as rootstock As scion 2.48 1.00 2.04 As rootstock 1.71 1.89 1.93
228 We m a y n o t e here t h a t , g r o w i n g freely, t h e vigour o f t h e " 1 5 " r o o t as o p p o s e d to t h a t of t h e s h o o t w o u l d be expressed b y multiple s h o o t s at the collar or as suckers. It is possible, t h e r e f o r e , t h a t a m u l t i - s t e m m e d b u s h f o r m m a y , in s o m e cases, be associated w i t h a r o o t s y s t e m o f sharply greater g r o w t h p o t e n t i a l t h a n t h a t o f t h e same c l o n e as a stem. First flowering
Most o f us have n o t i c e d t h e association with d w a r f i n g r o o t s t o c k s o f p r e c o s i t y in flowering and c r o p p i n g o f t h e scion. Here again, o u r impressions are based o n relatively few g e n o t y p e s , e.g. the apples M9, M26 and -MM106 and, less directly, Q u i n c e C. Tables V I I a n d V I I I give flowering r e c o r d s f o r spring 1 9 7 3 o f the e x p e r i m e n t s a l r e a d y described f o r apple a n d cherry. O f the q u i n c e s o n l y C 8 4 scions in 1 9 7 3 f l o w e r e d save f o r a single f l o w e r o n o n e Q u i n c e A. T h e m e a n n u m b e r s o f flowers per tree f o r C 8 4 / A , C 8 4 / C and C 8 4 / C 8 4 were 12, 19 a n d 2.5, respectively. These n u m b e r s are in inverse o r d e r o f vegetative vigour o f r o o t s t o c k , b u t t h e m o s t v i g o r o u s scion g e n o t y p e is t h e first to flower. Q u i n c e C is sterile. The data p r e s e n t e d indicate t h a t p r e c o c i t y , t h o u g h o f t e n associated w i t h r e d u c e d vegetative vigour, m a y be d e t e r m i n e d i n d e p e n d e n t l y in t h e individual TABLE VII First flowering in apple, 1973. Mean number of inflorescences per tree
~
Scion \RootstockS<
M9a
M26
M M l l l Rootstock means
M9a M26 MMlll
55 14 3
1 3 0
0 0 0
Scion means
24
1
0
19 6 1
TABLE VIII First flowering in cherry, 1973. Mean number of flowers per tree
F1~2/1
"A5 . . . .
48"
Rootstock means
1 7 11
3 3 4.5
2.5 6 3.5
2 5 6
6
3.5
2
--
Rootstock F12/1 "15" "48" Scion means
229 g e n o t y p e : in t h e e x a m p l e s q u o t e d , p r e l i m i n a r y t h o u g h t h e d a t a are, a full range is a p p a r e n t f r o m close inverse c o n n e c t i o n with vigour to i n d e p e n d e n c e a n d also, possibly, o f differences in g e n o t y p e influence a c c o r d i n g t o w h e t h e r it is p r e s e n t as r o o t s t o c k o r scion respectively. DISCUSSION T h e results o f t h e e x p e r i m e n t s m u s t n o t be r e g a r d e d as c o n v e y i n g w i t h e x a c t i t u d e t h e relative vigour o f t h e individual g e n o t y p e studied w h e n p r e s e n t either as s h o o t , or as r o o t , in t h e c o m p o u n d trees. Nevertheless, w h a t is clearly a p p a r e n t is striking c o n f i r m a t i o n t h a t while such relative vigour m a y a p p r o a c h the e x p e c t e d u n i t y in s o m e g e n o t y p e s , it m a y d e p a s t m a r k e d l y in others. S u c h p h e n o m e n a will p r o v e o f considerable interest to p h y s i o l o g i s t s and h o r t i c u l t u r a l i s t s alike and, in fact, also t o all w h o use grafting t e c h n i q u e s in research, e.g. virologists and physiologists. It appears, t h e r e f o r e , t h a t t h e practical potentialities o f r o o t s t o c k research, and especially of t h e use o f n e w g e n o t y p e s as r o o t s t o c k s , has y e t t o be fully e x p l o r e d and, f u r t h e r , t h a t we shall n o t fully u n d e r s t a n d , and t h e r e b y use t o fullest p o t e n t i a l , either o u r r o o t s t o c k s or o u r scions w i t h o u t m o r e basic, r a t h e r t h a n p u r e l y applied, s t u d y . This has lessons, f o r all p o m o l o g i c a l research, f o r such e x a m p l e s c o u l d be r e p e a t e d endlessly. I pose a final q u e s t i o n : are field, as distinct f r o m l a b o r a t o r y , studies in basic c r o p p h y s i o l o g y , t o o heavily o v e r - s h a d o w e d , o n t h e o n e h a n d , b y applied c r o p - a r e a e x p e r i m e n t a t i o n , a n d o n the o t h e r b y l a b o r a t o r y - s c a l e studies o f t o o r e s t r i c t e d scopes or o n trees t o o y o u n g t o r e p r e s e n t t h e d e v e l o p e d n o r m a l tree? REFERENCES Barlow, H.W.B., 1971. Effect of cropping on growth of the apple tree. Annu..Rep. E. Malling Res. Stn for 1970, 52--53. Dudney, P.J., 1971. The effect of rootstock on pruning on the growth pattern of an apple tree. Annu. Rep. E. Malling Res. Stn for 1970, 60--63. Halton, R.G., 1923. The influence of rootstock upon tree fruits. Proc. VIIth Int. Hort. Cong., Amsterdam, 94--112. Halton, R.G., 1928. The behaviour of certain pears on quince rootstocks. J. Pore. Hort. Sci., 7: 216--233. Maggs, D.H., 1957. Extreme growth rates of scions. Ann. Bot., London, 21 : 539--554. Maggs, D.H., 1962. A constant pattern of growth in young apple trees. Nature, 194: 250--252. Parry, M.S., 1970. Heat-treated clone of East Malling Quince C as a pear rootstock. Proc. 18th Int. Hort. Congr. Tel-Aviv 1,170, abstr. 333. Pearce, S.C., 1953. Field experimentation with fruit trees and other perennial plants. Technol. Comm. Commonw. Bur. Hort. and Plant. Crops, 23: 70p. Sax, K., 1950. The effect of the rootstock on the growth of seedling trees and shrubs. Proc. Amer. Soc. hort. Sci., 56: 166--168. Trowell, G.F., 1972. The stock/stock experiment. Annu. Rep. E. Malling Res. Stn for 1971, 56--57.
230
Tubbs, F.R., 1973. Research fields in the interactions of rootstocks and scions in woody perennials. Hort. Abstr., 4 3 : 2 4 7 - - 2 5 3 and 325--335. Vyvyan, M.C., 1955. Inter-relation of scion and rootstock in fruit trees. Ann. Bot. N.S., 19: 401--423.
ROOTSTOCK/SCION
RELATIONS
IN HORTICULTURAL
CROP
PHYSIOLOGY
F.R. T U B B S
John Innes Institute, Norwich (Great Britain) F o r m e r l y of East Malling R e s e a r c h S t a t i o n , M a i d s t o n e ( G r e a t B r i t a i n ) ( R e c e i v e d J a n u a r y 16, 1 9 7 4 )
ABSTRACT T u b b s , F.R., 1 9 7 4 . R o o t s t o c k / s c i o n r e l a t i o n s in h o r t i c u l t u r a l c r o p p h y s i o l o g y . Scientia Hort., 2: 2 2 1 - - 2 3 0 . A p r e l i m i n a r y r e p o r t is m a d e of t h e results o f g r o w t h studies o n c o m p o u n d t r e e s f o r m e d o f all c o m b i n a t i o n s , as scion a n d as r o o t s t o c k , o f t h r e e clones, c h o s e n t o cover a wide r a n g e o f vigour, o f apple, quince, a n d cherry. U n d e r t h e c o n d i t i o n s o f t h e o r c h a r d e x p e r i m e n t a n d w i t h t h e clones used, n o d i s t i n c t i o n was f o u n d b e t w e e n i n f l u e n c e o n t r e e size of a n y a p p l e c l o n e w h e n p r e s e n t as t h e scion or w h e n p r e s e n t as t h e r o o t s t o c k . Major d i s t i n c t i o n s in i n f l u e n c e as s c i o n or as r o o t s t o c k were, h o w e v e r , f o u n d in t h e case o f c e r t a i n q u i n c e a n d c h e r r y clones. E v i d e n c e as t o t h e p r e c o c i t y o f f l o w e r i n g of t h e scions o f c o m p o u n d t r e e s i n d i c a t e s t h a t p r e c o c i t y m a y o c c u r i n d e p e n d e n t l y o f a d w a r f i n g influence.
INTRODUCTION Scion/rootst0ck effects,'proven or reported by experienced horticulturalists, have been recorded among woody perennials over a very wide range of orders and families. The great range of rootstock/scion interaction in all aspects of growth and reproduction of the compound tree is well illustrated in pomological literature. A general survey of the whole field has recently been published by Tubbs (1973) as two review articles in Horticultural Abstracts, to which reference should be made for relevant citations. The early workers at East Mailing, vied with by Dutch and German horticulturalists and disputed by those in America who placed all emphasis on the importance of scion influence or of stem tissues, laid the foundations of further critical study of such effects. They enabled clear recognition of the problems posed by the major interactions they found between the characteristics of growth and fruiting of the scion on the one hand and the "vigour" of the rootstock on the other. Growth studies early indicated the need for explanation of the means whereby rootstock and scion mutually adjusted their growth such 'that, whether fruiting on the one hand, or non-fruiting on
222
the other, under given environmental and cultural conditions, the ratios of scion weight to rootstock weight were independent of the size of the tree resulting from t h a t mutual interaction. We are now entering the exciting stages when explanation can be sought through painstaking analysis of those hormonal relations adumbrating or controlling the seasonal and correlated activity of meristems together with the a m o u n t and ultimate distribution in tissue formation or energy reserves, in roots as in shoots, of the nett assimilate of the tree. The experiments now reported will, it is hoped, later provide unique material for further such analysis by those who are undertaking the basic studies in this field at East Malling. It was here that Vyvyan (1955) early recognised the need for critical growth studies as basic to the search for verifiable hypotheses as to the mechanisms of the striking mutual influences exerted by rootstock and scion. His experiments from 1927 onwards were later developed by Maggs (1962) on a longer term basis; these in turn have been succeeded by the meticulous and even longer term experimentation now being carried out by Barlow (1971), Dudney (1971), and Trowell (1972). Vyvyan's main approach was based on the then novel procedure of studying the growth of c o m p o u n d trees formed by the use, both as scions and as rootstocks, of clonal apples (rootstocks) in all combinations. Such experiments clearly required longer duration than the two years of Vyvyan's first experiment, as was recognised later. The studies of Trowell (1972) are entirely of the vegetative growth of deblossomed trees, the role of fruiting in the growth of root and shoot being now well d o c u m e n t e d (Barlow, 1971). It is to be noted, however, t h a t the emphasis in such studies had always been on apple with its established clones of k n o w n vigour, rather than on quince, plum or cherry. MATERIALS AND METHODS Experiments are in progress on all four species, apple, quince, plum, cherry, based on well replicated comparisons of three clones of each, in all their nine possible combinations. The tree-size data (October 1972) are from freely growing trees of three seasons' growth from working, deblossomed but unpruned save for the formation in the nursery year of a clean scion stem of at least 60 cm above the union. The apples were budded high (25 cm) in summer 1969, the quinces and cherries bench-grafted winter 1969/1970 on rooted stool or layer-bed shoots of one year's growth, as were the plums, to be reported later, in 1971/ 1972. The rootstock was thus a year (quince and cherry) or two years (apple) old when the scion started into growth. It is considered that the subsequent three seasons' growth was sufficient to allow of the c o m p o u n d trees reaching mutual adjustment between rootstock and scion over initial size and 'age' inequalities but not necessarily, of course, a final size relationship. The flowering records, taken in spring 1973, are in all cases the first flowering
223 save for one or two isolated blossoms on occasional trees of M9a/M9a in spring 1972 - - t o o few to justify inclusion. All clones, save M9a (carrying the three latent apple viruses only), were free of k n o w n viruses. The conclusions t o be drawn f r o m experiments of this t y p e are restricted t o evidence as to t h e behaviour of each clone: (1) as a scion above its own r oot s and also above the roots of, here, t he two o t h e r genotypes; (2) as a r o o t s t o c k , below its own scion and also below the scions of, here, the two o th er genotypes; (3) in interaction o f r o o t s t o c k and scion i.e. behaviour of particular rootstock/scion combinations departing f r om the consistency t o be e x p e c t e d f r o m (1) and (2). An efficient e x p e r i m e n t of this t y p e should thus include all combinations of genotypes selected as examples covering a wide range of vigour and o f potential p r eco city and fruitfulness. It m a y be recalled t hat among the apple ro o t s to ck s first studied b y V y v y a n was M4, which was included following Halton (1923) in order t o test (though w i t h o u t conclusive result) the then novel possibility that the r o o t and s hoot of the same clonal g e n o t y p e might differ in their intrinsic growth potential and t h e r e b y also in their growth controlling influence in t he m ut ual interaction of r o o t s t o c k and scion in the c o m p o u n d tree. However, it was n o t until 1950 t h a t the possibility received s u p p o r t f r o m the w or k of Sax (1950); Maggs (1957) r e p o r t e d striking experimental evidence from plums. T he experimental results comprise observations on vegetative growth and on first flowering T he f o r m e r ones, to be presented in Tables I--VI, were subjected to logarithmic t r a n s f o r m a t i o n and back-transformation according t o Pearce (1953). This is a statistical device making use of the fact t hat the distribution of data, o f t e n departing f r o m normal as to t r e a t m e n t effects in small samples, mo re nearly approaches normal when t ransform ed in this way. The data in Tables I--VI are f r o m back-transformation. EXPERIMENTAL RESULTS Vegetative g r o w th in apple
The apple e x p e r i m e n t consists o f the nine possible combinations o f three genotypes with ninefold replication, widely spaced in single tree plots. These were the dwarfing M9a; the m o d e r a t e l y dwarfing, after initial vigorous growth, M26; and the semi-vigorous MMlll. Table I shows the mean total length of all scion stems and branches achieved after three growing seasons o f the scion. It is immediately apparent t h a t n o t only are there distinct differences in vigour b etween th e three genotypes, but that these are of the same order w h e t h er as scion or as r o o t s t o c k . Main effects and differences are all significant, save t h a t as r o o t s t o c k s M26 is just n o t significantly different f r o m MMlll at this stage of growth of t he
224 TABLEI Total length (m) of scion extension growth in apple after three growing seasons October, 1972
R•
M9a M26 MMlll
M9a
M26
MMlll
4.0 9.3 9.1
8.4 13.4 18.2
8.7 20.1 25.2
Weighted means for each, as scion and as rootstock As scion 6.6 13.6 16.1 As rootstock 7.0 12.7 16.4 t r e e s . B e h a v i o u r o f i n d i v i d u a l c l o n e s as r o o t s t o c k a n d as s c i o n is v e r y similar. This c o n c l u s i o n is s u p p o r t e d b y t h e d a t a f o r h e i g h t of s c i o n a b o v e t h e u n i o n ( T a b l e II). Main effects of scion and r o o t s t o c k varieties are very highly significant and clear cut, there being no interaction specific to particular combinations. B e h a v i o u r as s c i o n o r as r o o t s t o c k is a g a i n similar. TABLE II Height of scion above union (m) in apple after three growing seasons October, 1972
M9a M26 MMlll
M9a
M26
MMlll
1.08 1.61 1.55
1.55 2.05 2.09
1.42 1.80 1.94
Weighted means for each, as scion and as rootstock As scion 1.39 1.88 1.71 As rootstock 1.34 1.81 1.84
We c a n c o n c l u d e , t h e r e f o r e , t h a t h e r e t h e r e is no e v i d e n c e of d i f f e r e n t i a l v i g o u r b e t w e e n tissues o f t h e s e t h r e e g e n o t y p e s (i.e. in t r e e s t h r e e y e a r s o l d a n d u n i n f l u e n c e d b y d i f f e r e n t i a l p r e c o c i t y o f f r u i t i n g ) w h e n p r e s e n t as s c i o n or as r o o t s t o c k r e s p e c t i v e l y in t h e c o m p o u n d t r e e . T h i s is n o t , of c o u r s e , evidence t h a t such differences w o u l d n o t occur with o t h e r clones t h a n these, o r u n d e r d i f f e r e n t c i r c u m s t a n c e s e.g. Mg ( V y v y a n , 1 9 5 5 ; Maggs, 1 9 6 2 ) .
225
Vegetative growth in quinces T u r n i n g t o quinces, all c o m b i n a t i o n s o f t h r e e clones w e r e used w i t h 18 f o l d r e p l i c a t i o n , w i d e l y spaced, in single t r e e plots. T h e s e were: Q u i n c e A, Q u i n c e C, and Q u i n c e C84, all virus free. R e f e r e n c e s t o t h e t w o f o r m e r a b o u n d in p o m o l o g i c a l literature; P a r r y ( 1 9 7 0 ) has s h o w n t h a t t h e d w a r f i n g e f f e c t , relative t o Q u i n c e A, o f Q u i n c e C w h e n use~d as a r o o t s t o c k f o r p e a r cultivars arises n o t so m u c h f r o m d i f f e r e n c e s in vigour i n f l u e n c e in t h e earlier years b u t r a t h e r f r o m t h e heavier and earlier c r o p p i n g o f t h e scion i n d u c e d b y Q u i n c e C as r o o t s t o c k . Q u i n c e C84 is an East Malling s e l e c t i o n , b y far t h e m o s t vigorous (in its e f f e c t o n t h e C o n f e r e n c e pear scions) o f all t h o s e studied. T h e b u s h y g r o w t h o f quinces p r e c l u d e d such detailed measurem e n t s a f t e r t h r e e growing seasons as f o r apple and cherry. D a t a are, h o w e v e r , available f o r t o t a l length o f t h e t h r e e longest laterals and f o r height o f scion a b o v e u n i o n a f t e r t h r e e growing seasons f r o m grafting. Table III s u m m a r i z e s t h e d a t a f o r t o t a l length. TABLE III Total length of three longest laterals (m) in quince after three growing seasons October, 1972
A C C84
A
C
C84
1.79 1.81 1.81
1.42 1.45 1.54
1.76 1.93 1.95
Weighted means for each, as scion and as rootstock As scion 1.81 1.47 1.88 As rootstock 1.65 1.72 1.76 T h e r e is n o i n t e r a c t i o n , i.e. n o e f f e c t specific to p a r t i c u l a r c o m b i n a t i o n s . T h e overall e f f e c t s o f scion, t o g e t h e r w i t h t h o s e o f r o o t s t o c k , are highly significant, P = 0.001 and P = 0.01, respectively. Clearly, t h e g e n o t y p e s behave q u i t e d i f f e r e n t l y in their t w o roles, Q u i n c e A being more vigorous as a scion t h a n as a r o o t s t o c k , Q u i n c e C being less vigorous in its i n f l u e n c e as a scion t h a n as a r o o t s t o c k (c.f. H a l t o n , 1 9 2 8 ) , and Q u i n c e C84 resembling t h e t h r e e apple g e n o t y p e s studie~l in t h e similarity o f its i n f l u e n c e in t h e t w o roles. This c o n c l u s i o n is strongly r e i n f o r c e d b y t h e d a t a f o r scion h e i g h t (Table IV). T h e b e h a v i o u r s o f differing c o m b i n a t i o n s are highly individual ( i n t e r a c t i o n P = 0.001). Again Q u i n c e A and Q u i n c e C e x e r t q u i t e d i f f e r e n t influences o n t h e c o m p o u n d tree, a c c o r d i n g as t o w h e t h e r t h e y are p r e s e n t as scion or as r o o t s t o c k . Q u i n c e C84 e x e r t s similar influences in b o t h roles.
226 TABLE IV H e i g h t o f s c i o n a b o v e u n i o n ( m ) in q u i n c e a f t e r t h r e e growing seasons O c t o b e r , 1 9 7 2
\-~Scion
Quince A
Quince C
Quince C84
1.67 1.70 1.78
1.34 1.28 1.32
1.51 1.76 1.61
Rootstock \`
Quince A Quince C Quince C84
W e i g h t e d m e a n s f o r each, as s c i o n a n d as r o o t s t o c k As scion 1.72 1.31 1.63 As rootstock 1.50 1.57 1.56
Again, these data provide no evidence t h a t some ot her three quince genotypes might n o t behave as did the three chosen apples. What t h e y do is to provide evidence of c o m p l e x i t y in r o o t s t o c k / s c i o n relations n o t previously apparent, i.e. the possible occurrence o f differential influence, as scion and as r o o t s t o c k , by a single g e n o t y p e of quince. Vegetative g r o w t h in cherry
The evidence obtained f r om the cherry experiment was even m o r e striking. The trees were planted in a widely spaced eightfold replication of the nine combinations o f three genotypes, with num e rous b o u n d a r y guards. Owing to bad weather conditions after planting, during the 1 9 6 9 / 1 9 7 0 winter, the original design was severely compromised. However, thereafter all surviving trees grew and developed normally and well. I am particularly indebted to Dr. Pearce and his staff of the Statistics Section of East Malling Research Station for their comprehensive study of all the data presented, but particularly for enabling the following summaries of the cherry growth to be drawn despite such initial difficulties. The three clones were the well-known East Malling F 1 2 / 1 , of m o d e r a t e vigour, and two recent selections, t he very dwarf Fb 2/58 (15) and the vigorous Fb 2/58 (48), now to be referred to as " 1 5 " and " 4 8 " , whose capabilities as r oot s t oc ks are as y e t largely u n e x p l o r e d The figures for F 1 2/ 1 on its o w n roots must be regarded as indicative only, owing t o low replication of this one combination. Data are available for t he total length of scion growth produced in three scion growing seasons and for height of scion above union by the same date, O c t ob er 1972. Table V presents the data for total length. The overall significance of t he differences shown is again high (P = 0.001). There are clear overall differences between scions, while in root st ocks it is F 1 2 / 1 that stands out as the m or e dwarfing. The outstanding contrast is b e t ween the respective influences o f " 1 5 " as scion and as r o o t s t o c k . The sheer magnitude o f this difference is very striking; in F12/1 and " 4 8 " the same effect is observable, though to lesser e x t e n t and of opposite sign.
227 TABLE V Total length (m) of scion growth in cherry after three growing seasons October, 1972 ~Scion
F12/1
"15
48"
Rootstoc~-F12/1 "15" "48"
6.3 12.6 12.6
2.1 6.2 5.8
19.5 35.5 35.5
Weighted means for each, as scion and as rootstock As scion 10.0 4.2 29.0 As rootstock 6.4 14.0 13.7 Arithmetic means for each, as scion and as rootstock As scion 10.5 ' 4.7 30.2 As rootstock 9.3 18.2 18.0 T h e r e is c l e a r e v i d e n c e h e r e , n o t a l o n e o f b o t h s c i o n a n d r o o t s t o c k d i f f e r ences and of that individuality of each combination of pairs of genotypes to which we are accustomed, but also both that a dwarf clone may possess a p o t e n t i a l l y v i g o r o u s r o o t s y s t e m as i n " 1 5 " a n d a l s o t h e r e v e r s e , as in " 4 8 " . The highly significant effects for height of scions in Table VI are here associated with scion differences, rootstock differences being insignificant. Again both F12/1 and "15" exert markedly different influences in the comp o u n d t r e e as s c i o n a n d as r o o t s t o c k : o t h e r d a t a i n d i c a t e t h a t t h e c o n t r a s t o f r o o t s t o c k e f f e c t s s h o w n b y T a b l e s V a n d V I m a y a r i s e in p a r t f r o m t h e relatively small number of extension shoots and greater mean length on scions over F12/1 and, with "15" (over F12/1 especially) their relatively very small length. TABLE VI Weight of sciona ~ b ~ v e union (m) in cherry after three growing seasons October, 1972 ion
F12/1\ "'-
"15 . . . .
2.23 2.63 2.57
0.89 1.05 1.07
48"
Rootstock~ F12/1 "15" "48"
2.00 1.99 2.14
Weighted means for each, as scion and as rootstock As scion 2.47 1.00 2.08 As rootstock 1.58 1.79 1.81 Arithmetic means for each, as scion and as rootstock As scion 2.48 1.00 2.04 As rootstock 1.71 1.89 1.93
228 We m a y n o t e here t h a t , g r o w i n g freely, t h e vigour o f t h e " 1 5 " r o o t as o p p o s e d to t h a t of t h e s h o o t w o u l d be expressed b y multiple s h o o t s at the collar or as suckers. It is possible, t h e r e f o r e , t h a t a m u l t i - s t e m m e d b u s h f o r m m a y , in s o m e cases, be associated w i t h a r o o t s y s t e m o f sharply greater g r o w t h p o t e n t i a l t h a n t h a t o f t h e same c l o n e as a stem. First flowering
Most o f us have n o t i c e d t h e association with d w a r f i n g r o o t s t o c k s o f p r e c o s i t y in flowering and c r o p p i n g o f t h e scion. Here again, o u r impressions are based o n relatively few g e n o t y p e s , e.g. the apples M9, M26 and -MM106 and, less directly, Q u i n c e C. Tables V I I a n d V I I I give flowering r e c o r d s f o r spring 1 9 7 3 o f the e x p e r i m e n t s a l r e a d y described f o r apple a n d cherry. O f the q u i n c e s o n l y C 8 4 scions in 1 9 7 3 f l o w e r e d save f o r a single f l o w e r o n o n e Q u i n c e A. T h e m e a n n u m b e r s o f flowers per tree f o r C 8 4 / A , C 8 4 / C and C 8 4 / C 8 4 were 12, 19 a n d 2.5, respectively. These n u m b e r s are in inverse o r d e r o f vegetative vigour o f r o o t s t o c k , b u t t h e m o s t v i g o r o u s scion g e n o t y p e is t h e first to flower. Q u i n c e C is sterile. The data p r e s e n t e d indicate t h a t p r e c o c i t y , t h o u g h o f t e n associated w i t h r e d u c e d vegetative vigour, m a y be d e t e r m i n e d i n d e p e n d e n t l y in t h e individual TABLE VII First flowering in apple, 1973. Mean number of inflorescences per tree
~
Scion \RootstockS<
M9a
M26
M M l l l Rootstock means
M9a M26 MMlll
55 14 3
1 3 0
0 0 0
Scion means
24
1
0
19 6 1
TABLE VIII First flowering in cherry, 1973. Mean number of flowers per tree
F1~2/1
"A5 . . . .
48"
Rootstock means
1 7 11
3 3 4.5
2.5 6 3.5
2 5 6
6
3.5
2
--
Rootstock F12/1 "15" "48" Scion means
229 g e n o t y p e : in t h e e x a m p l e s q u o t e d , p r e l i m i n a r y t h o u g h t h e d a t a are, a full range is a p p a r e n t f r o m close inverse c o n n e c t i o n with vigour to i n d e p e n d e n c e a n d also, possibly, o f differences in g e n o t y p e influence a c c o r d i n g t o w h e t h e r it is p r e s e n t as r o o t s t o c k o r scion respectively. DISCUSSION T h e results o f t h e e x p e r i m e n t s m u s t n o t be r e g a r d e d as c o n v e y i n g w i t h e x a c t i t u d e t h e relative vigour o f t h e individual g e n o t y p e studied w h e n p r e s e n t either as s h o o t , or as r o o t , in t h e c o m p o u n d trees. Nevertheless, w h a t is clearly a p p a r e n t is striking c o n f i r m a t i o n t h a t while such relative vigour m a y a p p r o a c h the e x p e c t e d u n i t y in s o m e g e n o t y p e s , it m a y d e p a s t m a r k e d l y in others. S u c h p h e n o m e n a will p r o v e o f considerable interest to p h y s i o l o g i s t s and h o r t i c u l t u r a l i s t s alike and, in fact, also t o all w h o use grafting t e c h n i q u e s in research, e.g. virologists and physiologists. It appears, t h e r e f o r e , t h a t t h e practical potentialities o f r o o t s t o c k research, and especially of t h e use o f n e w g e n o t y p e s as r o o t s t o c k s , has y e t t o be fully e x p l o r e d and, f u r t h e r , t h a t we shall n o t fully u n d e r s t a n d , and t h e r e b y use t o fullest p o t e n t i a l , either o u r r o o t s t o c k s or o u r scions w i t h o u t m o r e basic, r a t h e r t h a n p u r e l y applied, s t u d y . This has lessons, f o r all p o m o l o g i c a l research, f o r such e x a m p l e s c o u l d be r e p e a t e d endlessly. I pose a final q u e s t i o n : are field, as distinct f r o m l a b o r a t o r y , studies in basic c r o p p h y s i o l o g y , t o o heavily o v e r - s h a d o w e d , o n t h e o n e h a n d , b y applied c r o p - a r e a e x p e r i m e n t a t i o n , a n d o n the o t h e r b y l a b o r a t o r y - s c a l e studies o f t o o r e s t r i c t e d scopes or o n trees t o o y o u n g t o r e p r e s e n t t h e d e v e l o p e d n o r m a l tree? REFERENCES Barlow, H.W.B., 1971. Effect of cropping on growth of the apple tree. Annu..Rep. E. Malling Res. Stn for 1970, 52--53. Dudney, P.J., 1971. The effect of rootstock on pruning on the growth pattern of an apple tree. Annu. Rep. E. Malling Res. Stn for 1970, 60--63. Halton, R.G., 1923. The influence of rootstock upon tree fruits. Proc. VIIth Int. Hort. Cong., Amsterdam, 94--112. Halton, R.G., 1928. The behaviour of certain pears on quince rootstocks. J. Pore. Hort. Sci., 7: 216--233. Maggs, D.H., 1957. Extreme growth rates of scions. Ann. Bot., London, 21 : 539--554. Maggs, D.H., 1962. A constant pattern of growth in young apple trees. Nature, 194: 250--252. Parry, M.S., 1970. Heat-treated clone of East Malling Quince C as a pear rootstock. Proc. 18th Int. Hort. Congr. Tel-Aviv 1,170, abstr. 333. Pearce, S.C., 1953. Field experimentation with fruit trees and other perennial plants. Technol. Comm. Commonw. Bur. Hort. and Plant. Crops, 23: 70p. Sax, K., 1950. The effect of the rootstock on the growth of seedling trees and shrubs. Proc. Amer. Soc. hort. Sci., 56: 166--168. Trowell, G.F., 1972. The stock/stock experiment. Annu. Rep. E. Malling Res. Stn for 1971, 56--57.
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Tubbs, F.R., 1973. Research fields in the interactions of rootstocks and scions in woody perennials. Hort. Abstr., 4 3 : 2 4 7 - - 2 5 3 and 325--335. Vyvyan, M.C., 1955. Inter-relation of scion and rootstock in fruit trees. Ann. Bot. N.S., 19: 401--423.