Branch development in custard apple (cherimoya 'Annona cherimola' Miller X sugar apple 'A. squamosa' L.) in relation to tip-pruning and flowering, including effects on production

Abstract

Custard apple has cryptic axillary buds, hidden from view by the base of the petiole. This has led to confusion about custard apple’s flowering habit. Flowering only occurs during early branch development, and can be forced at any time of the growing season simply by removing leaves. Here, we show that flowering is terminal, not extra-axillary, and that the apparent continuation of the main stem beyond the flower is, instead, a sympodial branch. Secondary (including sympodial) branching only occurs during early branch development. Thereafter, axillary bud release is inhibited by the subtending leaf. Here, we show that summer tip-pruning of all branches arrests canopy development until the following spring owing to this inhibition. Although summer tip-pruning prevented new vegetative growth in the canopy, fruit size decreased relative to the control trees by ca. 23%. The reason for this decrease was probably related to increased carbon limitation to growth given that dawn water soluble and total nonstructural carbohydrate concentrations were lower in the tip-pruned trees. Thus, it appears that the reduced competition between fruit development and new vegetative growth in the tip-pruned trees was more than matched by lower photosynthetic capacity in the arrested canopy. Trees grown inside a shade-house were more vigorous than those grown outside. The difference in vigour had little effect on fruit size.