Agronomic and physiological responses of mature ‘Rojo Brillante’ persimmon grafted onto Diospyros lotus and Diospyros virginiana under spring-regulated deficit irrigation in Mediterranean conditions

Abstract

This study assessed the effects of spring-regulated deficit irrigation (RDI) strategies on the physiological and agronomic performance of a ‘Rojo Brillante’ persimmon (Diospyros kaki) orchard grafted onto Diospyros lotus and D. virginiana rootstocks. The trial was conducted from 2016 to 2019 in a commercial orchard located in Llíria (Valencia, Spain), under Mediterranean climate conditions. RDI was applied during late spring at increasing water restriction levels, while control treatments received non-limited irrigation. Results showed that RDI did not reduce yield per tree, even under severe water deficits, and consistently improved irrigation water productivity by up to 21 % in D. lotus and 31 % in D. virginiana compared to fully irrigated controls. The reduction in fruit drop observed in RDI treatments led to a 30 % increase in harvested fruits in D. lotus and 42 % in D. virginiana. On average, fruit drop-to-flowering ratios were lower under RDI (36.5 % in D. lotus, 68.6 % in D. virginiana) than in fully irrigated controls (49.9 % and 81.6 %, respectively). D. lotus trees showed more stable yields and a favourable vegetative-reproductive balance, while D. virginiana exhibited a different water stress response pattern in the seasonal dynamics of stem water potential, which is used to characterise differences in plant water status rather than intrinsic drought tolerance. Still, D. virginiana trees produced lower and more variable yields under both irrigation regimes, likely due to higher fruit drop and a potential biennial bearing pattern. Overall, the findings support spring RDI as a viable strategy to enhance irrigation water productivity in persimmon orchards.