PMAX AS RELATED TO LEAF - FRUIT RATIO AND FRUIT ASSIMILATE DEMAND IN PEACH

To estimate the effect of leaf:fruit ratio on peach leaf light-saturat ed photosynthesis, experiments were conducted on the early maturing cv . Alexandra in 1992 and late maturing cv. Suncrest in 1992, 1993 and 1 994. In early May, the leaf:fruit ratios of bearing shoots were adjust ed. The exchange of assimilate between the shoot and the rest of the t ree was prevented by girdling the base of the shoot. Leaf photosynthes is measurements were made under saturating irradiance using a portable leaf photosynthesis system. Our results show that there was a signifi cant effect of the leaf:fruit ratio on leaf light-saturated photosynth esis (Pmax). There was a reduction of Pmax when the leaf:fruit ratio was high. To describe the effect of fruit demand on photosynthesis, we : developed a hyperbolic model in which we assumed that Pmax is a func tion of fruit demand. The model is defined by two parameters: Pmax, th e potential light-saturated photosynthesis, and K-D, the initial slope of the response curve of Pmax vs. fruit demand. We found no differenc e between cultivars and among years, so we developed a model which uti lized all data.