The effect of irrigation regime on histological parameters of Japanese plum fruits (‘Angeleno’).

The response of fruit growth to irrigation depends on the cellular processes which form the fruit. We compared plum mesocarp (pulp) growth and development under two irrigation regimes: full irrigation (FI) that provided 100% of estimated crop evapotranspiration (ETc) and regulated deficit irrigation (RDI) without irrigation from 56 to 120 days after full bloom (DAFB) and full irrigation for the rest of the season. The experiment was performed in 2012 in a high-density plum (Prunus salicina ‘Angeleno’, on Mariana 2624 rootstock) orchard in La Orden regional experimental station (Extremadura, southwest Spain). Fruit central transverse mesocarp sections were observed by microscope, and mesocarp area, mesocarp cell number and mesocarp cells area determined at the onset of the deficit period (70 DAFB), the end of that period (120 DAFB) and at harvest (180 DAFB). Following the deficit period, fruit fresh weight in the deficit treatment was 68% of fully irrigated and mesocarp area, mesocarp cell number and mesocarp cells area were 31, 17 and 18% less, respectively. At harvest the deficit irrigated fruits had partially recovered, reaching 80% fresh weight of the control, and all cellular parameters and tissue sizes were similar to the fully irrigated fruits. These results confirm the capacity for plum fruit growth recovery following mid-season water stress, and that both cell and tissue processes contribute to recovery.