IMPLICATIONS OF PRUNING AND TRAINING PRACTICES TO CARBON PARTITIONING AND FRUIT DEVELOPMENT IN APPLE
Studies of apple carbon production, partitioning and fruit development in relation to canopy microclimate and time of season were conducted with ‘Empire’ apple over several years. Fruit growth rates within thinning trials demonstrated the importance of early growth during the first 4 to 6 weeks after bloom (AFB), to fruit set and final fruit size potential. Maintenance of fruit growth rates appears to be required for fruit set, and fruit abscission rates are correlated to fruit growth rates. Seasonal shading studies have shown that moderate shade had clearly detrimental effects on fruit growth rates at 4 weeks AFB, and just before harvest. Shade at 2 weeks AFB and in midseason at 10 and 14 weeks AFB, however, had little effect on fruit growth. Results from 14CO2 labeling and shoot carbon balance studies confirm earlier reports that exposed growing extension shoots begin carbon export after about 10 to 12 leaves have unfolded. Shading can markedly delay onset of export from extension shoots. Early cessation of shoot growth allows more rapid export from extension shoots. In an average canopy it appears that fruit growth during the critical cell division period (the first 4 to 5 weeks AFB) is supported primarily by spur leaves and short, terminated extension shoots. These results suggest some goals of pruning and training for optimizing fruit set and fruit size that are consistent with both empirically developed pruning and training rules and carbon balance/partitioning. The primary emphases are on 1) obtaining high exposure of the spur canopy at 3 to 4 weeks AFB, 2) controlling extension shoot vigor and inducing a high percentage of new shoots to terminate early, and 3) avoiding excessive shade on spurs and shoots.
Lakso, A.N. and Corelli Grappadelli, L. (1992). IMPLICATIONS OF PRUNING AND TRAINING PRACTICES TO CARBON PARTITIONING AND FRUIT DEVELOPMENT IN APPLE. Acta Hortic. 322, 231-240