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.

► H2O2 accumulation in response to ‘Gala’ apple fruit wounding was modulated by fruit maturity.
► Efficient wound healing was associated with production of H2O2 upon wounding.
► More mature fruit showed a loss in the ability to produce H2O2 upon wounding.
► Wound-healing ability declined with fruit ripening.
► Fruit ripening attenuated wound-induced defense resistance.