Maximum Fruit Growth Potential and Seasonal Patterns of Resource Dynamics During Peach Growth

Abstract

Maximum fruit growth potential, the growth attained by fruits when they are grown under optimal environmental conditions in the presence of a non-limiting supply of resources, was estimated for two peach [ Prunus persica (L.) Batsch] cultivars that differ in the timing of resource demand for reproductive growth. Maximum potential fruit growth was estimated on trees that were heavily thinned at bloom. On these trees, resource availability exceeded resource demand for fruit growth. For both cultivars, the mean dry weights of fruits grown on unthinned trees were approximately half the mean dry weights of fruits grown on trees that were heavily thinned at bloom, indicating that fruit growth was source-limited on unthinned trees. Comparison of the seasonal patterns of relative growth rate of fruits on unthinned and heavily thinned trees indicated the source-limited fruit growth occurred during distinct periods of the growing season. On the early maturing cultivar, source-limited fruit growth occurred from 300 degree-days after bloom until harvest (4·5-10 weeks after bloom). On the late maturing cultivar, source-limited fruit growth occurred from 200-900 and 1600-1900 degree-days (3·5-12 and 18-20 weeks) after bloom. Although the final dry weight of fruits on the early maturing cultivar was only half that of fruits on the late maturing cultivar, the potential net sink strength of fruits was significantly higher on the early than the late maturing cultivar throughout the entire growth period of the early maturing cultivar. Resource availability for fruit growth was similar on the early and late maturing cultivars, indicating that selection for early maturing fruits has not changed the patterns of resource availability for fruit growth.