Pear fruit growth under regulated deficit irrigation in container-grown trees

Abstract

The effect of regulated deficit irrigation (RDI) on fruit growth was studied for pear trees ( Pyrus communis L. ‘Barlett’) grown in 120 l isolated containers. Two irrigation treatments were applied in consecutive seasons (1996 and 1997) but on different trees each year. The Control treatment was watered to non-stress conditions using stem water potential (Ψ stem) and Penman ETo as a guide for the application of water. The RDI treatment received an average of 15% of the Control applied water from 32 to 60 DAFB (days after full bloom), the latter part of pear fruit development Stage I. Before 32 DAFB and after 60 DAFB, RDI was irrigated as the Control. Tree water status (leaf and stem water potential, leaf conductance and net assimilation rate at midday) and fruit growth parameters were measured periodically during both years. Additionally, in 1997, anatomical measurements of fruit growth (radial distance along fruit cortex tissue, cell number per radial distance and cross-sectional area) were made at the end of the deficit period and at harvest. Minimal Ψ stem values during the RDI deficit period were about −1.4 MPa, indicative of moderate stress, and fruit growth was less in RDI than in the Control. The integral of water stress during the deficit period was linearly correlated with smaller cell size in the fruit cortex, whereas cell number was unaffected. When full irrigation was resumed and during Stage II fruit development, the fruit growth rate remained higher in the Control than in RDI, despite fruit osmotic adjustment and slightly higher tree water status of RDI. At harvest, RDI fruit size was smaller than the Control. The apparent contradiction between these results and studies which report a recovery of fruit growth after deficit irrigated period may be caused by differences in growth conditions.