Resistance of gibberellin-treated persimmon fruit to Alternaria alternata arises from the reduced ability of the fungus to produce endo-1,4-β-glucanase.

ABSTRACT Black-spot symptoms, caused by Alternaria alternata, developed in persimmon fruits during prolonged storage at -1°C. A preharvest treatment with gibberellic acid (GA3) extended the storage life of the fruit by delaying both black-spot development and fruit softening. Conversely, treatment of persimmon fruits with paclobutrazol (PBZ), an inhibitor of gibberellin (GA) synthesis, enhanced black-spot development and fruit softening during storage. Production of endo-1,4-β-glucanase (EC 3.2.1.4, EG) by A. alternata in culture and in the presence of cell walls from PBZ-treated fruits as the carbon source, was enhanced by 150% over production in the presence of cell walls from control fruits, whereas endoglucanase (EG) production in the presence of cell walls from GA3-treated fruits was reduced by 49% relative to controls. To determine the importance of EG in symptom development, A. alternata EG was purified from a culture-inducing medium. It had a molecular mass of 41 kDa, its optimal pH and temperatur...