Physiological and biochemical mechanisms leading to blossom-end rot in greenhouse-grown peppers, irrigated with saline solution

Blossom-end rot (BER) is a fruit physiological disorder that occurs under salinity stress and is known to be associated with impairment of calcium translocation to the fruit tip. In the present study we investigated the possibility that oxidative stress is part of the causative mechanism of BER in pepper (Capsicum annuum L.). Pepper plants of two cultivars; ('Silica', not sensitive to BER and '107', sensitive) were grown in a greenhouse and irrigated with nutrient solution made up with either desalinated water (control - E.C 1.9), or saline water (salinity - E.C. 3.7-7.0). Irrigation was applied by a circulation system. BER symptoms were observed in '107' throughout the experiment while in 'Selica' the amount of BER was minimal. BER occurrence was significantly increased under salinity in the sensitive but not in the insensitive cultivar. The fruit calcium concentration in both sensitive and resistant cultivars was not changed by salinity. The oxidative stress-related enzymatic activities in the fruit were dependent on the fruit developmental stage. Under salinity, oxygen radical and hydrogen peroxide production, and NAD(P)H oxidase activity were all enhanced at the most sensitive developmental stage. In contrast, the anti-oxidative activities of superoxide dismutase (SOD) and catalase were not affected by salinity. The results suggest that generation and scavenging of oxygen free radicals may be part of the mechanism that leads to the appearance of BER symptoms in pepper fruits under saline conditions. We suggest that measures to alleviate oxidative stress in greenhouses would reduce the risks of blossom-end rot in peppers.