GENOTYPIC DIFFERENCES IN THE LEAF EMERGENCE RATE OF YOUNG PEACH-TREES

Leaf emergence was studied on main and first-order shoots of peach and nectarine [Prunus persica (L.) Batsch.] trees belonging to nine stand ard cultivars, during their first growing season. The number of emerge d leaves was recorded on main shoots (originating from the grafted bud s) and on first-order shoots (inserted directly on main shoots). Simil arly shaped leaf emergence curves were observed on main and first-orde r shoots for all the cultivars. Leaf emergence rate decreased graduall y as the number of leaves increased. The number of emerged leaves coul d be modeled as a monomolecular function of accumulated thermal units. Significant differences were found between cultivars in a multiple an alysis of variance of the model parameters, for main and first-order s hoots. The ranking of the cultivars was similar for both types of shoo ts. Leaf emergence rate was lower on first-order shoots than on main s hoots. Differentiating between shoot types is necessary for a reliable comparison of genotypes.