Control of alternaria black spot in persimmon fruit by a mixture of gibberellin and benzyl adenine, and its mode of action

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In Israel, alternaria black spot (ABS) disease, caused by Alternaria alternata, is the main postharvest factor that reduces quality and impairs storability of persimmon fruit Diospyros kaki cv. Triumph. The fungus infects the fruit in the orchard and remains quiescent until harvest, or renews its development just before harvest, following rain or high humidity; it then preferentially colonizes the stem-end of the fruit. Recent findings suggest the importance of ethylene and respiration during early fruit growth as factors influencing maturity, crack development, and occurrence of ABS in the stem end of the fruit. We tested the effects of the growth regulator Superlon, a mixture of gibberellin (GA4+7) and benzyl adenine (BA), applied at 40μgmL−1 once a month during three consecutive months, on fruit physiological responses during growth and on ABS occurrence during storage at 0°C. Superlon treatments during the early stages of fruit growth, i.e., starting 40 days after fruit set (daf), applied once monthly during three consecutive months, inhibited ethylene and CO2 production in the stem end. Treatments applied starting 100daf enhanced cell proliferation under the fruit cuticle. Regardless of application timing, Superlon delayed chlorophyll degradation, and reduced fruit cuticle cracking and ABS susceptibility during the late stages of fruit growth and during storage. Present results suggest that the phytohormone, acting as a modulator of host physiological responses that result in delayed fruit maturation, is a main factor in enhanced resistance to ABS at harvest and during storage.