Effects of crop load on fruit water relations and fruit growth in peach

Many studies have reported the effect of crop load on leaf water relations of fruit trees but none have dealt with the effect of crop load on water relations of the fruit and how such an effect might influence fruit growth. This is of interest because it could improve our understanding of the relationship between crop load and fruit size. In this study, we measured fruit water potential, fruit osmotic potential, fruit turgor potential and fruit growth, and leaf water potential and leaf conductance on nine-year-old 'Yanco Queen' peach 'Prunus persica (L) Batsch' trees carrying different levels of crop load. The trees were trained on Tatura trellis and had been either left unthinned (heavy crop load: 450 fruit per tree in 1986 and 560 fruit per tree in 1987) or were thinned (light crop load: 310 fruit per tree). Trees carrying the heavy crop load had lower fruit water potential and higher fruit osmotic potential, and consequently lower fruit turgor potential compared with trees carrying a light crop load. Fruit growth during the day was also less and fruit shrinkage was greater in the heavy crop than in the light crop, and this appeared to be correlated with the lower fruit water potential and turgor potential in the heavy crop. Leaf water potential was also lower in the heavy crop compared with the light crop but crop load did not appear to influence tree water relations significantly through changes in leaf conductance. It was concluded that increased crop load increased fruit water deficit which reduced fruit growth. Hence, the reduction in fruit size commonly associated with increased crop load may be due, at least in part, to the effect of crop load on fruit water relations. It is possible that more frequent irrigation or even misting of trees could improve fruit water relations and increase fruit size in heavily cropped trees to a greater extent than in lightly cropped trees.