INVASIVENESS OF ASPERGILLUS-FLAVUS ISOLATES IN WOUNDED COTTON BOLLS IS ASSOCIATED WITH PRODUCTION OF A SPECIFIC FUNGAL POLYGALACTURONASE

Aspergillus flavus produces several pectolytic enzymes during invasion of cotton bolls. To investigate the importance of pectinases in this process, pectinase production by 16 isolates of A. flavus, with known ability to spread between cotton boll locules and rot them, was quantified by a cup-plate assay. Aggressiveness of isolates during the infection process was correlated with their ability to secrete pectinase(s) on sterilized cotton-seed, on pectin-containing liquid media, and in living host tissues. Four isolates with reduced ability to spread through boll tissues and rot them lacked a major endopolygalacturonase activity that always was present in highly aggressive isolates. Thus, certain pectolytic enzymes produced by A. flavus during host infection contribute to fungal aggressiveness.