Effect of Fruiting on Net CO2 Assimilation Rates of Peach and Nectarine Trees
Growth of peach fruits is characterized by a double-sigmoid curve; two periods of rapid enlargement (stages I and III) separated by a lag phase (stage II). Seasonal net CO2 assimilation rates (NAR) were compared in leaves from fruiting and non-fruiting (deblossomed) trees of `Harrow Diamond' (early), and `Vivid' (mid-summer) peach (Prunus persica L. Batsch.) and `Fantasia' (late) nectarine (P. persica) to determine 1) the influence of fruits on photosynthesis and 2) the relationship between NAR and fruit growth. Seasonal trends in NAR tended to be qualitatively similar among the three cultivars, despite genotypic and phenotypic differences. There was a distinct increase in NAR at the time of horticultural fruit maturity (stage III) of each cultivar. Shortly after harvest, NAR rates declined. The average seasonal NAR of fruiting `Harrow Diamond', `Vivid', and `Fantasia' trees was 9%, 11%, and 10% higher, respectively, than that of corresponding non-fruiting trees. Parallel data for total chlorophyll was 28%, 20%, and 19% higher, and specific leaf weight (SLW) was 3%, 5%, and 6% lower, respectively. A negative correlation between NAR and SLW may indicate a feedback inhibition of photosynthesis.