Wound-induced H2O2 and resistance to Botrytis cinerea decline with the ripening of apple fruit

Fruit ripening is a developmental process and is associated with increased susceptibility to mechanical injury, which favours Botrytis cinerea infection. Using ‘Gala’ apples harvested at different stages of ripening, we demonstrated that wounding can activate initial H₂O₂ accumulation and wound healing ability to defend against B. cinerea penetration. Delaying the harvest date attenuated those responses. Superoxide dismutase, peroxidase and catalase, which are all involved in H₂O₂ metabolism, were differentially activated by wound stress depending on the stage of fruit maturity. Mature fruit were less able to respond to wounding by increasing phenylalanine ammonia lyase and peroxidase activity, which are associated with reduced phenolics and lignin content in local wound sites. The reduced response in late-harvested fruit contributes to the fruit ripening-induced loss of wound healing ability and increases susceptibility to B. cinerea. In addition, the rapid increase of H₂O₂ content immediately after wounding in early-harvested fruit was followed by increased phenylalanine ammonia lyase and peroxidase activity. In late-harvested fruit, the reduced ability to increase phenylalanine ammonia lyase and peroxidase activity in response to wounding was consistent with ripening-reduced generation of H₂O₂ early after wounding, leading to reduced resistance to B. cinerea. Thus, H₂O₂ accumulation in response to wounding is modulated by fruit maturity and is required for efficient wound healing and resistance to B. cinerea.