Modulation of tolerance of Hamlin sweet orange grown on three rootstocks to on-tree oleocellosis by summer plant water balance supply

Citrus fruit is prone to on-tree oleocellosis (OTO), which decreases its fresh market value due to deterioration in the fruit peel. This study aimed to evaluate the effects of Lichi16-6 trifoliata (Poncircus trifoliate, LC), Goutoucheng sour orange (Citrus aurantiunt, GT), and Rangpur lime (C. limonia Osbeck, RI) rootstocks on the occurrence of OTO, plant water status, reactive oxygen species (ROS) scavenging capacity of 12-year-old Hamlin sweet orange (C. sinensis Osbeck) trees in both 2014 and 2015 cropping seasons. The results showed that Hamlin trees grown on RI. maintained higher water potential and relative water content (RWC) in leaves and fruit peels as well as higher transpiration in the morning and afternoon compared with scions grown on the other two rootstocks. This improved water status in the morning resulted in a lower diurnal range of rind oil release pressure (Delta RORP) and the incidence of OTO per tree (IOPT). However, although Hamlin trees grown on GT had a significantly higher transpiration in the morning, leaves of Hamlin trees grown on GT had the lowest transpiration in the afternoon compared with those grown on the other two rootstocks. This exacerbated water status in the afternoon resulted in higher malondialdehyde and ROS in leaves and severity of OTO per tree (SOPT). In conclusion, the tolerance of Hamlin sweet orange grown on three rootstocks to OTO was modulated by plant water balance supply during OTO-sensitive stage. Also, the Delta RORP and ROS scavenging capacity could be selected as indicators to assess IOPT and SOPT, respectively.