Assessment of Extracellular Enzymes Produced by Fungi Isolated from Muscadine Grapes

Muscadine grapes are a climacteric fruit and therefore post-harvest storage can be problematic due to latent fungal infections. Berry rot has been attributed to the fungus Colletotrichum gleosporides. However, we also consistently isolated Pestalotia sp. from rotten berries. Rots can be caused by the actions of extracellular hydrolytic enzymes that degrade plant cell walls. This study sought to characterize the extracellular enzymes produced by C. gleosporides and Pestalotia sp. The fungi were assessed for the ability to produce pectinases, cellulases, amylase and lipases, all hydrolytic enzymes. Additionally, they were tested for the production of (poly)phenol oxidases. Assessments of enzyme activities were completed with growth of the pathogens on solidified medium amended with the substrate as well as total protein containing the target enzymes isolated from liquid induction medium. All isolates of both fungi produced amylase and lipase. Pestalotia sp isolates generally exhibited higher cellulolytic and pectinolytic activity than C. gleosporides. Both fungi exhibited (poly) phenol oxidase activity, but Pestalotia sp. isolates consistently showed two isozymes (bands) compared to the one band produced by C. gleosporides isolates using gel electrophoresis. Precision breeding of muscadine grapes (cisgenics) for resistance to infection by fungal pathogens is in progress. When successful, extracellular wall-degrading enzymes, from berry rot fungi will be eliminated and longevity of postharvest storage of muscadine grapes improved.