Effect of relative humidity on production of extracellular pectolytic enzymes by Botrytis cinerea and Sclerotinia sclerotiorum

Abstract

B. cinerea and S. sclerotiorum growing in a nutrient medium on the surface of carrots at 20 °C produced significantly more extracellular pectolytic enzymes when the carrots were exposed to 94–96% relative humidity than when exposed to 98–100% relative humidity. Tests in which these organisms were grown in a nutrient solution containing pectic substances showed that they produced pectolytic enzymes in significant quantities only when readily metabolizable sources of energy (e.g. ethanol, carbohydrates) were not available. These results suggest that the low relative humidity increased enzyme production by concentrating nutrients on the carrot surface to the point where they inhibited growth of the organisms and stimulated enzyme production. Tests also showed that pectolytic enzyme activity on the surface of unwashed carrots stored 9 months at 0–1 °C was substantially higher at 90–95% relative humidity than at 98–100% relative humidity. The results indicated that reduced decay at 98–100% relative humidity was largely due to lower pectolytic enzyme production.