THE RELATION OF BARK MOISTURE TO THE DEVELOPMENT OF CANKER DISEASES CAUSED BY NATIVE, FACULTATIVE PARASITES: I. CRYPTODIAPORTHE CANKER ON WILLOW

Abstract

A close correlation was found to exist between the development of the willow bark canker, caused by Cryptodiaporthe salicina (Curr.) Weh., and the moisture content of the bark. When this was expressed as a percentage of the amount of water required to saturate the sample under experimental conditions, relative turgidities of 80% or more inhibited canker development which, however, occurred normally at lower percentages. Studies of the epidemiology of this disease in the Vancouver area afforded evidence in support of the limiting effect of bark moisture on canker development. Thus during the dormant season of 1957–58 the monthly average temperature was significantly higher than the minimum temperature for the growth of C. salicina on potato dextrose agar and the relative turgidity did not reach the inhibiting value of 80%. Cankers continued to develop throughout this period. During the growing season while temperatures were still more favorable for fungus development no extension of cankers occurred, apparently because, during the growing period, the relative turgidity was in excess of 80%. Canker development was prevented during the winter by placing dormant twigs in water, which likewise increased the moisture content of the bark above the 80% level.