Mechanisms of resistance to Botrytis cinerea in wounds of cured kiwifruits

Storage rot due to Botrytis cinerea is the major cause of postharvest losses in kiwifruit. Curing for 48 h at 15°C with high RH before storage at 0°C markedly improved the resistance of kiwifruits to Botrytis infections. The aim of this study was to investigate on the resistance mechanisms involved. In cured fruits, histological observations revealed the presence of an electron-opaque lamellar structure near the cell wall in a few cell layers close to the artificial wound where a positive reaction was observed due to suberin and also phenolics. Phenolic substances also observed in the cells under the pedicel scar of cured fruits were higher than in the uncured ones. Negative reactions were obtained for lignin, callose and gums. The activity of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO) as well as the concentration of endogenous phenolics were determined in the tissues close to the wounds. Compared to uncured fruits, PAL and PPO activities were higher (about ten times) in cured ones, followed by an increased level of soluble cinnamic acid derivatives.