Jujube fruit water relations at fruit maturation in response to water deficits

The fruit maturation stage is considered the optimal phenological stage for implementing water deficit in jujube (Zizyphus jujuba Mill.), since a low, moderate or severe water deficit at this time has no effect on yield, fruit volume or eating quality. However, no information exists at fruit water relations level on the mechanisms developed by Z. jujuba to confront drought. The purpose of the present study was to increase our understanding of the relationship between leaf and fruit water relations of jujube plants under different irrigation conditions during fruit maturation, paying special attention to analysing whether fruit size depends on fruit turgor. For this, adult jujube trees (cv. Grande de Albatera) were subjected to five irrigation treatments. Control plants (T0) were irrigated daily above their crop water requirements in order to attain non-limiting soil water conditions in 2012 and 2013. T1 plants were subjected to deficit irrigation throughout the 2012 season, according to the criteria frequently used by the growers in the area. T2 (2012), T3 and T4 (2013) were irrigated as T0 except during fruit maturation, in which irrigation was withheld for 32, 17 and 24 days, respectively. The results indicated that the jujube fruit maturation period was clearly sensitive to water deficit. During most of this stage water could enter the fruits via the phloem rather than via the xylem. From the beginning of water withholding to when maximum water stress levels were achieved, fruit and leaf turgor were maintained in plants under water deficit. However, a direct relation between turgor and fruit size was not found in jujube fruits, which could be due to an enhancement of a cell elasticity mechanism (elastic adjustment) which maintains fruit turgor by reducing fruit cells size or to the fact that jujube fruit growth depends on the fruit growth-effective turgor rather than just turgor pressure.