MAXIMUM VEGETATIVE GROWTH-POTENTIAL AND SEASONAL PATTERNS OF RESOURCE DYNAMICS DURING PEACH GROWTH

The maximum vegetative growth potential of two peach [Prunus persica (L.) Batsch] cultivars that differ in the timing of resource demand for reproductive growth was determined in terms of stem extension, stem and leaf dry weight accumulation, and trunk radial increment on defruited trees. The maximum vegetative growth potentials were similar on the two cultivars indicating that the greater partitioning of dry weight to vegetative growth frequently observed on early maturing cultivars compared to late maturing cultivars is the result of a shorter period of competition between reproductive and vegetative growth, rather than a genetic difference in vegetative growth potential. On both cultivars, stem extension and leaf dry weight accumulation ceased in mid-summer, however stem dry weight accumulation and trunk radial increment increase continued through the autumn. The presence of fruit did not have a detectable effect on the final stem length, stem dry weight or leaf dry weight on the early maturing cultivar, but it reduced final stem length and dry weight by 43 and 56%, respectively on the late maturing cultivar. The presence of fruit did decrease stem length, stem dry weight and leaf dry weight on the early maturing cultivar for 1 month prior to and 1 month after fruit harvest. Fruit decreased final trunk radial increment by 42 and 77 % on the early and late maturing cultivars, respectively. These reductions in vegetative growth indicate that resource partitioning to vegetative growth was reduced by competition with fruit growth. Comparison of stem relative extension rates and stem and leaf relative growth rates on fruited and defruited trees indicated that vegetative growth was resource-limited shortly after vegetative bud break on fruited trees of both cultivars. This period of resource-limited vegetative growth corresponded to a period of resource-limited fruit growth identified in an earlier study. During the period of resource-limited vegetative growth, assimilate supply was low due to low leaf area index, and carbohydrate demand was relatively high due to high vegetative and reproductive growth potentials, creating resource-limited growth conditions. (C) 1995 Annals of Botany Company