Scientia Horticulturae, 39 (1989) 201-209 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
201
Orchard Response of Micropropagated Sour Cherry and Apple Cultivars P. ROSATI' and DARIA GAGGIOLI2
~Centro Studi Tecnica, Frutticola C.N.R., Bologna, (Italy) 2Istituto di Coltivazioni Arboree, Universitd, Bologna (Italy) (Accepted for publication 26 October 1988 )
ABSTRACT Rosati, P. and Gaggioli, D., 1989. Orchard response of micropropagated sour cherry and apple cultivars. Scientia Hortic: 39: 201-209. The field performance of sour cherry and apple tissue -cultured (TC) trees has been investigated in comparison with standard-propagated (SP) trees. In sour cherry, TC trees were compared with trees grafted on mazzard and on the clonal rootstock cultivars 'Colt', CAB 6P and CAB l l E . The TC trees were the less productive and had the lowest production efficiency. The canopies of all the trees reached the same size at the end of the fifth season in the field. The CAB 6P clonal rootstock appeared the most interesting for high yield and good fruit size. In apple, the TC trees were the most vigorous and had the same cumulative production ( 19811986) as the trees on MM106 because of high yields from TC trees in 1985 and 1986. A noticeable difference between TC trees and those on MM106 existed in production efficiency and canopy size in favour of the trees on MM106. Only in 1986 the TC trees lost the juvenile character shown in the early years in the field. Keywords: Sour cherry trees; spur apple trees; tissue culture. Abbreviations: SP = standard propagated trees, grafted on rootstocks; TC = tissue culture propagated trees on their own roots.
INTRODUCTION
T h e t r a d i t i o n a l w a y t o p r o d u c e t h e t r e e s u s e d t o e s t a b l i s h f r u i t o r c h a r d s is by grafting the rootstock with a scion cultivar either in the nursery or directly i n t h e o r c h a r d s . T h i s t i m e a n d m o n e y - c o n s u m i n g t e c h n i q u e is r e l a t e d t o t h e f a c t t h a t s c i o n c u l t i v a r s a r e n o t t r u e t o t y p e if r a i s e d f r o m s e e d s a n d d o n o t propagate easily by layering or cuttings. In recent years micropropagation through axillary bud proliferation has become a useful tool to multiply both rootstock and scion cultivars of several top
202
fruit species. This technique shows great potential for mass propagation at lower cost and in a shorter time than traditional methods. The micropropagation of scion cultivars has given rise to questions concerning self-rooted, tissue-culture-originated (TC) trees, namely: (1) their correspondence to the phenotype shown by standard propagated trees; (2) their capacity to resist soil-borne diseases and to affect tree vigour in comparison to the traditional rootstocks; (3) their bearing capacity and cropping efficiency in comparison to SP trees. Fairly good information exists on the field performance of TC originated strawberries and Rubus, while more limited information is available on fruit trees. This may be related to the fact that a definite statement on woody plants performance requires a longer period of time. Flowering and fruiting of TC apple trees of the cultivar 'Stayman' planted in the orchard in spring 1982 after growing for 1.5 years in the nursery were delayed by at least 1 year compared with SP trees of similar age and compared with sibling TC trees that were not pruned back at the time of planting (Zimmerman, 1986). Since the TC scions were larger at planting than the SP ones, it could be envisaged that the same heading back applied to all the scions could have delayed the TC scions more than the SP ones. On the other hand, it appears that peach trees do not behave in the same way (as reported by Martin et al., 1983 ), because TC peaches and nectarines bore an important crop 1 year after planting. TC pear trees cultivar 'Bartlett', in comparison with SP trees on quince rootstocks (Sansavini et al., 1985), lost their initial higher vigour and lower production efficiency only when they reached their sixth year. We have already shown that the TC trees of 2 sour cherry cultivars and of the 'Perleberg 3' strain (spur-type) of cultivar 'Golden Delicious' apple begin to bear fruit later than SP trees, in spite of the fact that TC cherry trees had a smaller trunk size compared with SP. TC apple trees, by contrast, were much more vigorous than trees grafted on MM106 and M M l l l (Rosati and Gaggioli, 1987). After 5 years of experimenting with apple cultivars ('Cox's Orange Pippin', 'James Grieve', 'Greensleeves' and 'Golden Delicious'), the initial differences between TC and SP plants showed a tendency to disappear (Webster et al., 1985 ). Flowering of TC trees was delayed for 1-2 years compared with SP trees. It is possible that the initial negative traits of TC plants could have been influenced by their smaller size when planted, as they were 1 year younger than the SP (budded on rootstocks which were 2 years older). We report here the 1986 results of our trials initiated in 1981-1982 to compare the effect of the propagation method (SP sv. TC ) on orchard performance of sour cherry and apple cultivars.
203 MATERIAL AND METHODS S o u r c h e r r y . - TC plants (15-20-cm tall) of cultivars 'Meteor' and 'Montmorency' sour cherries, established out of sterile culture in the fall 1980 and overwintered in the open, were planted in the nursery in February 1981. At the same time, 4 rootstocks (mazzard, and the clonal 'Colt', CAB l l E and CAB 6P, the latter two being semi-dwarfing clones of P r u n u s c e r a s u s selected at Bologna University) were grafted with propagating material collected from the same tree used for the collection of the TC explants. The scions were transplanted from nursery to orchard using a split-plot design involving the 2 cultivars, the 5 root systems (4 rootstocks and the own-rooted TC trees) with 5 replications of 1 tree. Trees were spaced 4 X 4 m and trained as free spindles. - The explants of 'Perleberg 3' strain (spur-type) of 'Golden Delicious' apple were collected in 1979 from a tree showing definite spur habit. In February 1980, established plants obtained in vitro were planted in the nursery and at the same time the two clonal rootstocks (MM106 and M M l l l ) were grafted, collecting the grafting material from other trees of the same clone showing a definite spur habit. All mother trees are still consistent, to date, in their spur habit. Trees were transplanted from the nursery to the orchard in January 1981 using a randomized block design with 6 replications of 10 trees spaced 4 X 2 m and trained as free spindles. We did not cut back the scions at planting and subsequent pruning was limited to the minimum. Data collected in 1986 included trunk diameter, as previously measured each year, measured in February, 15 cm above the union, and the calculated trunk cross-section area. The total production picked from each tree was weighed and the apples picked in each tree were counted. As in 1985, the flowers were counted in the central 4 apple trees of each plot and classified on the basis of the age of the supporting wood as: spurs (2 or more years old) and brindilles or long shoots ( 1 year old). The percentage of flowers carried in the lower part of the canopy (less than 120 cm from ground level) was calculated. In October the maximum extension reached by the tree canopies was measured: on the row, across the row and height. The canopy volume was calculated as follows: 4/3 n a b 2 (where a 1/2 height, b = 1/2 average tree diameter; Westwood, 1978). Apple.
RESULTS S o u r c h e r r y . - The lower production shown, previously up to 1985, by the TC trees compared with the SP trees, as a combined effect of later bearing and juvenility, was confirmed in 1986. We found no differences among the 4 rootstocks as total crop per tree. The cumulative 1983-1986 production enhanced this trend (Table 1). Tissue culture trees produced only half as much as the
2O4 TABLE 1 Sour cherry fruit production (kg tree - 1), 1986 and cumulative fruit production ( kg tree - 1), 19831986. Cultivar
Rootstock TC
Mean Mazzard
'Colt'
llE
6P
1986
8.3 8.8
16.1 20.2
14.4 18.5
18.6 23.3
18.9 23.7
15.3 b
'Montmorency' 1986 1983-1986
9.7 12.8
12.2 17.5
13.6 19.9
12.6 17.1
14.2 20.6
12.5"
Mean 1983 1983-1986
9.0 a 10.8 a
14.1 b 18.8 b
14.0 b 19.2 b
15.6 b 20.2 b
16.5 b 22.1 b
'Meteor' 1986 1983-1986
1983-1986
18.9"
17.6 ~
Mean separation in rows (among rootstocks) and in columns (between cultivars) by Duncan's multiple range test, 5% level. TABLE 2 Sour cherry trunk cross-section area (cm 2) and weight of pruning material (kg t r e e - 1), 1986 Cultivar
Rootstock
Mean
TC
Mazzard
'Colt'
' 11E'
6P
cm 2
'Meteor' cm ~ kg
77.1 3.9
89.1 3.8
115.0 3.9
102.3 3.6
88.4 3.9
94.4 b
'Montmorency' cm 2 kg
86.3 6.9
71.7 5.9
86.0 7.2
74.6 7.7
88.9" 7.7
81.5 a
Mean cm 2 kg
81.7 ~ 5.4"
80.4" 4.8 a
100.5 b 5.6"
88.5 ab 5.6"
88.7 "b 5.8"
kg
3.8"
7.1 b
Mean separation in rows (among rootstocks) and in columns (between cultivars) by Duncan's multiple range test, 5% level.
trees on mazzard, 6P and l l P clonal rootstocks in spite of the fact that they attained the same trunk size and the same weight of pruning material (Table 2). As a combined effect of these two factors, the TC trees had the lowest production index (Table 3 ). This negative fact was supported by the fact that,
205 TABLE3 Productivity index of sour cherries (cumulative production (kg tree -1) 1983-1986/trunk crosssection area (cm 2) 1986 Cultivar
Rootstock
'Meteor' 'Montmorency' Mean
Mean
TC
Mazzard
'Colt'
11E
6P
0.11 0.15 0.13 a
0.23 0.24 0.23 b
0.16 0.23 0.19 ab
0.23 0.23 0.23 b
0.27 0.25 0.26 b
0.20 a 0.22 ~
Mean separation in row (among rootstocks) and in column (between cultivars) by Duncan's multiple range test, 5% level. TABLE 4 Apple, 1986, weight of pruning material and trunk cross-section area. Tree canopy: spread in and across the row, height and volume
TC MM106 MMlll
Pruning weight (kg t r e e - 1)
Trunk cross-section (cm 2)
Tree canopy
Volume (m 3)
In the row (cm)
Across the row (cm)
Height (cm)
4.3 b 1.4 a 1.5 a
58.3 b 28.1 a 30.2 a
227 b 180 a 190 a
238 b 156 a 167 a
487 c 356 ~ 389 b
13.8 b 5.3 ~ 6.5 a
Mean separation within columns by Duncan's multiple range test, 5% level.
in October 1986, we found no differences (data not shown) among the canopy sizes of the different cultivar/rootstock combinations. Tree vigour, after 6 years, is shown by the average 4.3-m height and 3.2-m spread. Among the different rootstocks, 6P tended to combine the highest total production and production index with good fruit size. - Tissue culture trees in 1986 were the most vigorous, considering weight of pruning material, trunk cross-section and canopy expansion (Table 4 ); the TC trees also reached, in 1986, the highest production per tree, while their cumulative production, over the 5 trial years, did not differ from the trees on MM106 (Table 5 ). The production index of trees on MM106 Was much greater owing to the larger canopy size and volume of TC trees. In 1986, for the first time, we did not find any differences among the percentages of flowers in the lower part of the canopies between TC and grafted trees (Table 6); a progressive increase of the ratios between the percentages concerning TC and MM106 trees could be observed over the period 1984-1986 (0.44, 0.50 and 0.87 in the 3 years, respectively), showing a gradual disappearance of the juvenility trait in the TC trees. Apple.
206 TABLE 5 Apple, total production and fruit weight, 1986. Cumulative production 1982-1986 and productivity index (cumulative production/trunk cross-section area) 1986
TC MM106 MM111
1982-1986
Production (kg t r e e - ~)
Fruit weight (g)
Production (kg t r e e - 1)
Productivity index
30.0 b 20.4 a 15.3 a
220 a 207 ~ 214 ~
83.7 ~' 74.9 ~ 59.5 H
1.44 a 2.66" 1.97 ~
Mean separation within columns by Duncan's multiple range test, 5% level. TABLE 6 Apple, 1986, total number of inflorescences per tree, percentage in the lower part of the canopy (below 120 cm from ground) and distribution on wood of different ages: 2 or more years old, spurs, and 1 year old, brindilles and long shoots ( > 30 cm ) Inflorescences per tree
TC MM106 MMlll
Total no. tree -~
Below 120 cm (%)
On spurs (%)
On brindilles (%)
On long shoots (%)
237 b 135 ~ 150 a
49 a 56 a 56 ~
44 a 61 ~) 655
31 b 24 ~ 21 a
255 15a 14a
Mean separation within columns by Duncan's multiple range test, 5% level. TABLE 7 Number of laterals per tree (0.6-2.0 m from ground level) angle formed by the laterals and diameter of the laterals at 15 cm from their insertion on the central leader
TC MM106 MMlll
No. of laterals
Laterals/leader angle
Laterals diameter (mm)
24.75 21.7 a 24.35
60 a 64 b 61 a
16 b 11a 11"
Mean separation within columns by Duncan's multiple range test, 5% level. Inflorescence distribution in 1986 on wood of different ages confirms the previous year's results and points out that, for this important character, the TC trees perform as the standard trees of 'Golden Delicious' and differ from the trees with spur-growing habit (Rosati, 1975). The TC trees had a higher number of laterals, as reported also for 'Stayman'
207 by Zimmerman (1986), forming a smaller angle with the central leader, than the trees on MM106, while no differences were found with the trees on M M l l l . The laterals of the TC trees were thicker at their base than those of the grafted trees (Table 7). DISCUSSION The TC sour cherry trees showed the lowest cumulative production as a consequence of their delayed coming-into-bearing compared with SP trees and of their continued low production efficiency as expressed by the production/ trunk cross-section ratio. Also their efficiency per hectare is low because their canopy reaches the same size as that of the more productive trees on the other rootstocks, so production can not be increased through closer spacing. The TC apple trees had, as the TC cherry trees, the same 1-2-year delay in coming-into-bearing combined with vigorous vegetative growth. As a result of the large canopy at the end of fifth crop, they reached a very good value for production per tree, although it was not matched by a high production efficiency, expressed either by the production/trunk cross-section ratio or potential production per hectare. The vigorous growth was probably caused by the combined effect of the lack of production the TC trees had in the first 2 years (Fig. 1 ) and of the loss of the spur habit, which appeared evident from visual observation, from the distribution of the flowers on wood of different ages (which confirms what we observed in 1985) and from the size reached by the tree canopy. Such vigorous trees have to be more widely spaced than the much more efficient trees on MM106. Naturally, the loss of spur habit also affected the production efficiency of TC trees negatively. We recently observed TC trees of the same strain, originated by several explants we excised in 1983 from one tree showing a definite spur habit, and these 3~,~ D TF I
II MM 106
~ I~IM ',I '~ "--,
F
Fig. 1. Yearlyproduction (kg tree- 1) from 1982to 1986of TC appletreesand SP trees on MM106 and MM111clonalrootstocks.
208 young TC trees had already lost their spur habit. The same loss of spur habit (which was not observed, by contrast, in trees of 'Wellspur', a spur strain of 'Delicious' apple) was reported (Faedi and Cobianchi, 1986) in trees of'Starkspur Golden', another spur-type strain of 'Golden Delicious' apple, originated by hardwood cuttings; on the contrary, grafted trees originated by propagating material taken from the same mother trees were consistent in their spur habit. The reversion from spur to standard growth habit had been for a long time the major problem of the spur strains of 'Golden Delicious' apple. The 'Perleberg 3' strain has proven to be the most stable when compared with two other strains: 'Yellospur' and 'Starkspur Golden' (Faedi and Rosati, 1984), the percentage of reversion observed being very close to that recorded in the spur strains of 'Delicious' in which the phenomenon has negligible importance. The loss of the spur habit is most probably related to the differing chimeral structure of all these spur strains, and has not been sufficiently investigated up to now. It appears that trees are unable to keep their spur habit stable when vigorous vegetative growth occurs. This could also raise the question whether, at least in some strains, the spur habit is only an expression of a morphological determinism recalling epigenetic variance. We consider that, in the sixth year of growth, the TC apple trees finally lost their "juvenile" habit as, for the first time, flowers, in the lowest part of the canopy, had the same frequency as shown in SP trees on MM106 and M M l l l . From all available information it appears that orchard performance of selfrooted TC trees may be species (and probably cultivar) dependent. This means, particularly for apple trees, that further research and field evaluations are needed to sort out the advantages connected with the use of such vigorous trees that can be of particular interest in all areas where land shortage and cost do not represent a major problem. The research will need to point out cultivar response to this technique. Improvement to tree field performance may come using a different TC explant source (petals, as in some ornamentals, inducing TC plants to early blooming, Gimelli et al. ( 1984 ). ACKNOWLEDGEMENTS Research work supported by CNR, Italy. Special grant IPRA - - Sub-project 1, Paper no. 1225. D. Gaggioli was funded from 1 J a n u a r y 1982 with a grant from E.R.S.O., Cesena.
REFERENCES Faedi, W. and Cobianchi, D., 1986. Comportamento vegeto-produttivo di alberi autoradicati di melo. Atti Conv. La Coitura del Melo verso gli Anni '90. S.O.I., Cordenons, pp. 301-306. Faedi, W. and Rosati, P., 1984. Reversion in spur clones of'Delicious' and 'Golden Delicious'apple trees. Acta Hortic., 159: 57-61.
209 Gimelli, F., Ginatta, G., Venturo, R., Positano, S. and Buiatti, M., 1984. Plantlet regeneration from petals and floral induction "in vitro" in the mediterranean carnation (Dianthus caryophyllus L.). Riv. Ortoflorofruttic. Ital., 68: 107-121. Martin, C., Carre, M. and Vernoy, R., 1983. La multiplication v~g~tative in vitro des v~g~taux ligneux cultiv~s: cas des arbres fruitiers et discussion g~n~rale. Rev. Agron., 3: 303-306. Rosati P., 1975. Regression in 'Golden Delicious' spur apple trees. Ann. Ist. Sper. Fruttic., Roma, VI: 101-109. Rosati, P. and Gaggioli, D., 1987. Field performance of micropropagated peach rootstocks and scion cultivars of sour cherry and apple. Acta Hortic., 212: 379-390. Sansavini, S., Neri, D., Grandi, M. and Lane, W.D., 1985. Confronto fra portinnesti nanizzanti e alberi micropropagati di pero. Atti Inc. Frutt. I1 Rilancio della Coltura del Pero. S.O.I. Ferrara, pp. 23-30. Webster, A.D., Oehl, W.H., Jackson, J.E. and Jones, O.P., 1985. The orchard establishment, growth and precocity of four micropropagated apple scion cultivars. J. Hortic. Sci., 60: 169-180. Westwood, M.N., 1978. Temperate-zone pomology. Freeman, San Francisco, CA, p.223. Zimmerman, R.H., 1986. Propagation of fruit, nut, and vegetable crops - overview: 183-200. In: R.H. Zimmerman, R.J. Griesbach, F.H. Hammerschlag and R.M. Lawson {Editors), Tissue Culture as a Plant Production System for Horticultural Crops. Martinus Nijhoff, Dordrecht, pp. 183-200.