Changes in primary and secondary growth as influenced by crop load in 'Fantasmes((R))' apricot trees

The effect of crop load on the growth dynamics of individual shoots was ana lysed in apricot trees in the third growing season, comparing their develop ment at two initial locations dong the bearing branch. Growth dynamics were observed throughout the growing season, from April to August, and took int o account both primary growth (i.e. number of expanded leaves) and secondar y growth (i.e. basal diameter increment). Crop load influenced primary grow th rhythmicity and more precisely growth resumption within the growing seas on. The length of the growing period and the number of expanded leaves were more significantly reduced on shoots originated from a proximal position a long the branch than in a distal position. Thus, crop load enhanced the acr otonic distribution of branching. The allometric relationship between the b asal diameter and the number of expanded leaves per shoot was not dependent upon shoot type, location or crop load treatment. Arguments are provided s upporting the hypothesis that cambial growth occurring soon after the expan sion of the preformed leaves is responsible for cessation of primary growth . This competition was shown to be independent of crop load and to involve only vegetative organs. These results indicate that the sink demand of the secondary growth and the resulting competition with the primary growth shou ld be taken into account in the carbon economy of fruit trees, and that the competition between organs is not equally distributed between the organs o f a given type but depends on their relative location.