Effects of relative source-sink position within peach trees on fruit growth under water stress conditions

SummaryThe source-sink position of 3-year-old, potted ‘O’Henry’ peach trees was manipulated by arranging the sources and sinks in opposite positions in order to investigate the effect of directional movement of assimilates from source leaves to fruit sinks. Six different treatments were applied: 1) control-fully irrigated (C-FI), in which irrigation was applied to achieve non-stress conditions, without removal of either leaves or fruit; 2) control-deficit irrigated (C-DI), in which irrigation was reduced to obtain a moderate deficit, without removal of either leaves or fruit; 3) downward movement of assimilates-deficit irrigated (Down-DI), in which fruits from the upper part and leaves from the lower part of the tree were removed; 4) upward movement of assimilates-deficit irrigated (Up-DI), in which fruits from the lower part and leaves from the upper part of the tree were removed. The last two treatments [(5) and (6)] were identical to the Down-DI and Up-DI treatments, but source leaves and fruit sinks were isolated by girdling. Changes in stem water potential ( stem) and transpiration rate (T) were evaluated. Fruit growth analysis was based on the expected theoretical response of fruit dry mass gain to stem. The experimental conditions allowed expression of potential differences in carbon transport efficiency (i.e., the distance between leaves and fruits was sufficient to cause limitations on fruit growth) and the reserves originating from fruit-bearing shoots were relatively small (20%) in comparison with the requirements for optimum fruit growth. Under these conditions, fruits on Down-DI trees did not exhibit significant differences in their capacity to accumulate carbohydrates with respect to Up-DI fruits. The data appear to indicate that, under moderate water stress conditions, resistance to assimilate transport does not differ greatly between upward and downward movement within trees.