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

Interactions were investigated between irrigation and crop load on photosyn thesis, fruit growth and size, and fruit water relations of 'Braeburn' appl e. The irrigation treatments were a commercially irrigated control (CI) and deficit irrigation (DI) applied throughout the season. The crop load treat ments were commercial crop load (CCL) having six fruit per cm(2) of trunk c ross-sectional area and light crop load (LCL) having four. There were inter actions between irrigation and crop load on fruit water potential (Psi (fw) ), fruit turgor potential (Psi (fp)), and photosynthetic rate (Pn) during m id and late season, and on mean fruit weight at harvest. These parameters w ere the same for CCL and LCL under CI except for Psi (fp) which was lower i n CCL. Under DI they were lower in CCL than in LCL. For both crop loads DI reduced Psi (fw) and Psi (fp) early in the season but from mid-season Psi ( fp) was maintained through osmotic adjustment. Photosynthetic rates were lo wer 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 fo r CI and DI for LCL, but was lower in DI for CCL. Interactions between irri gation and crop load on fruit size could be due to effects on fruit water r elations and photosynthesis.