2017 ASHS Annual Conference

Hormesis is a phenomenon that describes various adaptive and beneficial responses of organisms to low levels of stressors of chemical, biotic or abiotic in nature. This phenomenon has been reported in plants since 1900’s, where herbicides such as glyphosate enhanced the accumulation sucrose in sugar cane plant. The application of UV-C hormetic phenomenon to fresh produce began in the 1990’s as a tool initially to reduce decay and later to delay senescence. Since the last decade, this concept is being investigated for improving and maintaining the quality of fresh fruits and vegetables, and more recently for enhancement and maintenance of phytochemical compounds in fresh produce during storage. The physiological and biochemical basis of induced disease resistance by UV-C hormesis has been established in a few crops, tomato fruit and carrot root that involves a multi-component system including hypersensitive-like reaction and phytoalexins, ultra-structural modification leading to the formation of a physical barrier reinforced with phenolic compounds, lignin and suberin, and pathogenesis-related proteins. Furthermore, UV-C hormesis has been shown to improve microbiological safety of minimally processed vegetables, and to enhance specific phytochemicals that are potentially beneficial to human health. Other abiotic stresses have also been examined as means of increasing phytochemicals; the most recurrent in the literature are UV-B, heat and ozone. Treatments with UV-B have been shown to increase the titers of flavonoids and glucosinolates in Brassica. Likewise, the application of heat and low doses of ozone have elevated the levels of total phenols in fruits. Despite these findings, the application of abiotic stresses, in most cases, is performed arbitrarily without clearly defining the hormetic dose for stresses for a specific crop leading to significant variations in the responses. Consequently, there is a need for standardization with respect to hormetic doses of abiotic stresses as well as a need to establish the biochemical mechanisms underlying the hormetic effects in postharvest crops.