Water relations, photosynthesis, growth, yield and fruit size of ‘Braeburn’ apple: Responses to deficit irrigation and to crop load

Abstract

SummaryInteractions were investigated between irrigation and crop load on photosynthesis, fruit growth and size, and fruit water relations of ‘Braeburn’ apple. The irrigation treatments were a commercially irrigated control (CI) and deficit irrigation (DI) applied throughout the season. The crop load treatments were commercial crop load (CCL) having six fruit per cm2 of trunk cross-sectional area and light crop load (LCL) having four. There were interactions between irrigation and crop load on fruit water potential (Ψfw), fruit turgor potential (Ψfp), and photosynthetic rate (Pn) during mid and late season, and on mean fruit weight at harvest. These parameters were the same for CCL and LCL under CI except for Ψfp which was lower in CCL. Under DI they were lower in CCL than in LCL. For both crop loads DI reduced Ψfw and Ψfp early in the season but from mid-season Ψfp was maintained through osmotic adjustment. Photosynthetic rates were lower in DI than in CI for both crop loads but differences late in the season were significant only for CCL. Mean fruit weight at harvest was similar for CI and DI for LCL, but was lower in DI for CCL. Interactions between irrigation and crop load on fruit size could be due to effects on fruit water relations and photosynthesis.