Báo cáo lâm nghiệp: "Correlative control of early stages of flower bud initiation in ’bourse’ shoots of apple (Malus x domestica Borkh. cv. Golden Deliciou"

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Nội dung Text: Báo cáo lâm nghiệp: "Correlative control of early stages of flower bud initiation in ’bourse’ shoots of apple (Malus x domestica Borkh. cv. Golden Deliciou"

Correlative control of early stages of flower bud initiation in ’bourse’ shoots of apple (Malus x domestica Borkh. cv. Golden Delicious) J. Crabbé J. Escobedo agronomiques, Gembloux, Belgique Facult6 des Sciences Morphog6n6se v6g6tale appliqu6e, renewed floral induction. There may be Introduction year-to-year irregularities due to competi- at the same site tion with fruit growing in fruit A better of flowering understanding (alternate bearing) or with nearby vegeta- trees would be obtained if we could pre- tive growth. dict where and when a flower is to appear. Our objectives were to determine what This is particularly true in those locations treatments could cause 90-100% of for the first time: where flowering occurs bourse buds to shift from the vegetative to predicted (Crabbe, 1984) with be they can the floral state and to define precocious a satisfying probability for fruit growers’ signs of this change in meristematic ac- purposes, but any precise physiological or tivity. biochemical approach requires more than probability. Consequently, although mere the start of floral initiation is rather accu- rately known in fruit species, sound Materials and Methods information about floral induction and evocation is still lacking. Six yr old apple trees, cv. Golden delicious, As a preliminary to this necessary pre- were used throughout. Bourses formed in the current year, on which young fruits were deve- diction problem, we began experimenting loping, were labeled in early spring. Later, some on apple ’bourse’ shoots. The bourse is bourses with short arrested shoots (i.e., spurs) the swollen basal part of an inflorescence and others with long shoots (ca 20-30 cm) axis at the onset of fruit development; it were further selected and treated separately. bears leaves whose axillary buds differen- Treatments, generally known to increase tiate and may grow out as shoots. The flower formation, though imperfectly interpreted on physiological grounds, were: branch ringing, bourse shoot can flower again in the young fruit removal from the treated bourse following years and so, by repeated and, on the long bourse shoots, summer prun- flowering, a cluster of stacked similar ing. These treatments were applied alone or in structures appears on old trees. Once combination, at different dates from mid-May to formed, a bourse is thus a known site for September.
Buds were sampled fortnightly on treated and (Fig. 3, top) and, together with ringing and control branches for dissection and primordia fruit removal, enabled full completion of counting, until the plastochron decrease floral initiation (Fig. 3, bottom). However, appeared as the earliest sign of floral initiation when applied too early, pruning made the (Fulford, 1966a, b, c; Abbott, 1977). Terminal uppermost buds break out immediately as buds of spurs and terminal and lateral buds on long shoots, intact or pruned, were considered leafy shoots. Depending upon the inser- separately. tion level of the bud, the best time for pruning shifted from late June for the lower buds to late July for the upper ones. Results Discussion and Conclusion The terminal buds of spurs began to form in early May. So all treatments from mid- May to early July appeared to increase A complete shift of the bourse buds to node formation within the bud. Neverthe- flower formation was thus obtained by fruit less, branch ringing and fruit suppression suppression on the bourse plus branch needed to be combined to obtain over ringing, when applied at a time compatible 90% flowering (Fig. 1, bottom). The most with the need to shorten the plastochron. precocious treatments seemed the most For lateral buds on long shoots, pruning active in terms of percentage of flowering, was a further requisite. although those applied from mid-June to The enhanced accumulation of nodes early July yielded the fastest response in within the bud was a good early marker of node number increase (Fig. 1, top). On this shift. But rneristematic activation was the average, a bud which reached over 18 itself a consequence of even more preco- nodes at the end of July presumably cious changes. Our results, repeated became floral. during 3 successive years, suggest that In the selected long shoots, growth we have the experimental system neces- arrest occurred after mid-June. At that sary to proceed further in this research. time, bud formation had already started in lateral buds. However, the terminal bud formed much faster so that, by late References August, it already had about 15 nodes, while the laterals lingered around 10-13 (Fig. 2, top). Once again, branch ringing Abbott D.L. (1977) Fruit bud formation in Cox’s and fruit removal combined, applied in Orange Pippin. Annu. Rep. Long Ashton Res. Sta. 1976 167-l,76 July, brought the terminal to 90% flow- ering, but failed to do so for the laterals Crabbe J. (1983) Vegetative vigor control over location and fate of flower buds in fruit trees. (Fig. 2, bottom). Acta Hortic. 149, 55-63 But pruning those long shoots, right Fulford R.M. (19 b, c) The morphogenesis 66a, 1 above the median lateral buds, remarka- of apple buds. I, II, III. Ann. Bot. 29, 167-180; bly increased node formation within these 30, 25-38; 209-2199