Protective role of foliar-applied melatonin against gray mold (Botrytis cinerea) in gerbera cut flower: A biochemical and pathological Insight

Gray mold (Botrytis cinerea), a major necrotrophic pathogen, significantly impairs the quality and postharvest longevity of cut flowers. This study investigated the protective effects of melatonin on the physiological, biochemical, and pathological responses of Gerbera jamesonii ‘Red Italian’ to B. cinerea. Gerbera plantlets, cultivated in a soilless system, were treated with foliar-applied melatonin at concentrations of 0, 100, 200, or 300 μM prior to inoculation with B. cinerea. Melatonin application, particularly at 200 μM, significantly enhanced chlorophyll content, stomatal conductance, and relative leaf water content, all of which declined markedly in non-inoculated controls. Furthermore, melatonin reduced ion leakage and lipid peroxidation in inoculated plants compared to non-treated inoculated plants. Antioxidant enzyme activities, including catalase and peroxidase, were significantly elevated in melatonin-treated, B. cinerea inoculated relative to non-treated plants. Notably, 100 μM melatonin doubled the total phenolic content (from 7.1 to 15.4 mg GAE/g FW) in inoculated plants compared to non-treated controls. Melatonin also increased phenylalanine ammonia-lyase activity and lignin accumulation, contributing to reduced disease severity. Consequently, these physiological and biochemical enhancements extended the vase life of cut flowers from 8.3 to 14.8 days. These findings position melatonin as a sustainable bioregulatory agent for enhancing disease resistance and postharvest quality in ornamental plants, supporting eco-friendly floriculture practices.