Abstract: The aims of this study were to optimize the culture conditions of Monilinia fructicola for the production of cell wall degrading enzymes (CWDE) and to clarify the role of the culture supernatant obtained as crude CWDE in the pathogenesis of brown rot caused by Monilinia fructicola in postharvest plums. The optimization of the culture conditions was carried out using one-factor-at-a-time and orthogonal array design methods. Besides, the pathogenesis was investigated by wounding and inoculating plum fruits with the crude CWDE and observing the incidence of brown rot. The results showed that the optimal culture conditions were as follows: culture time, 6 d; pH, 6.0; 3.5% sucrose as carbon source; and 2.5% KNO3 as nitrogen source. The crude enzymes produced by M. fructicola could cause brown rot of plum fruits. In addition, the activities of polygalacturonase (PG), pectin methylgalacturonase (PMG) in the fruits inoculated with the crude enzymes were enhanced, thereby leading to the conversion of insoluble protopectin to soluble pectin and cellulose reduced cellulose content and consequently accelerating the softening and rotting process.

Key words: brown rot, cell wall degrading enzymes, plum, pathogenesis