title: Cell wall-degrading enzymes ofDidymella bryoniaein relation to fungal growth and virulence in cantaloupe fruit.
abstract: Didymella bryoniaeis an important pathogen of cucurbits worldwide. Virulence factors ofD. bryoniaewere investigated in regard to fungal growth and the production of cell wall-degrading enzymes, polygalacturonase (PG), pectate lyase (PL), pectin lyase (PNL), β-galactosidase (β-Gal) and cellulase (Cx). Virulence levels of fiveD. bryoniaeisolates were determined by the severity of inoculated cantaloupe fruit decay. The highly virulent isolates had more mycelial growth than the moderately virulent isolates in different media. PG activities produced by the highly virulent isolates in shake cultures and in decayed fruit were greater than those of the moderately virulent isolates. PNL, but not PL, in decayed fruit was higher with the highly virulent isolates compared to the moderately virulent ones. The highly virulent isolates showed higher Cx activity than the moderately virulent ones in decayed fruit and in fruit tissue shake culture. β-Gal activities of the highly virulent isolates in pectin shake culture and in decayed fruit were greater than those of the two moderately virulent isolates although fruit also produced β-Gal. Protein analysis showed two fungal β-Gal isozymes in decayed fruit compared to those of healthy fruit. Correlation analysis indicated that the activities of PG, PNL, β-Gal and Cx in cultures and in decayed fruit positively correlated with fungal growth and fruit decay severity. The results of this study suggest that PG, PNL, β-Gal, and Cx appear to be virulence factors ofD. bryoniaein cantaloupe decay with PG and β-Gal as the most predominant fruit decay enzymes.
authors.affiliation: USDA-ARS, South Central Agricultural Research Laboratory, Lane, OK 74555.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.affiliation: USDA-ARS, South Central Agricultural Research Laboratory, Lane, OK 74555.
authors.forename: B D
authors.initials: BD
authors.lastname: Bruton
authors.affiliation: Department of Biology, East Central University, Ada, OK 74820.
authors.forename: C L
authors.initials: CL
authors.lastname: Biles
keywords: Cucumis melo; black rot; cellulase; pectate lyase; pectin lyase; pectolytic enzymes; polygalacturonase; β-galactosidase.