Influence of crop load on maximum daily trunk shrinkage reference equations for irrigation scheduling of early maturing peach trees

The effects of high crop load (unthinned trees, 22-23 fruits cm(-2) of trunk cross-sectional area (TCSA)), commercial crop load (3-4 fruits cm(-2) of TCSA), and no crop load (all fruitlets removed) on maximum daily trunk shrinkage (ME)S), trunk growth rate (TGR) and stem water potential (Psi(stem)) were studied during the fruit growth period and 20 days following harvest in fully irrigated early maturing peach trees, Prunus persica (L.) Batsch, cv. Flordastar. Even though crop load did not affect plant water status, the MDS and TGR values increased and decreased, respectively, as a result of the crop load effect. In this sense, for the same Psi(stem) value, there was a linear increase in MDS with crop load, with a slope of 6.6 mu m MPa-1 per unit of crop load increment. The effects of environmental conditions on daily MDS values were also dependent on crop load, suggesting that MDS reference values should be obtained by representing the relations between MDS and the climatic variables (daily mean air temperature, daily mean vapour pressure deficit and daily crop reference evapotranspiration) for a given crop load. The constancy of the relation between MDS and psi(stem) across crop load underlined the constancy of the elastic properties of the bark tissues. (C) 2009 Elsevier B.V. All rights reserved.