Verticillium wilt of tomatoes—the role of pectic and cellulolytic enzymes

Abstract

SUMMARYAn isolate of Verticillium albo‐atrum, highly pathogenic to tomato plants, secreted polygalacturonase (PG) on a variety of synthetic media. Particularly active filtrates were obtained from cultures on media containing mineral salts, casamino acids and pectin or polypectate. Pectates were degraded more rapidly than pectin. None of the filtrates had high cellulase or pectinesterase activity; the most active were from cultures with carboxymethyl cellulose or pectin as carbon sources.The fungus made little growth in exudates from xylem sap unless carbon sources were added, and then culture filtrates had appreciable PG and cellulase activity but very little pectinesterase activity. Saps from susceptible and resistant varieties gave similar results.The fungus was also grown on a synthetic sap based upon an analysis of xylem exudate. Results similar to those for xylem sap were obtained.Filtrates from cultures on dead stems of both varieties had little pectinesterase activity and a definite but relatively low PG and cellulase activity.Extracts from diseased plants had no PG or cellulase activity but had a considerably higher pectinesterase activity on fresh and dry weight bases. Exudates from xylem of diseased plants had no PG or cellulase activity but had a low pectinesterase activity which was slightly higher than that from healthy plants.The effects of different culture filtrates on cuttings is described. Filtrates with high PG activity produced some of the symptoms found in naturally diseased plants.Solutions of pectin, polypectate and carboxymethyl cellulose caused cuttings to wilt in very low concentrations; much higher concentrations were needed after solutions of these substances had been degraded by PG or cellulase.