Factors Affecting Cytosporo Canker Occurrence on Aspen

"Experiments were designed to determine how moisture content of aspen trees is related to infection and expansion of Cytospora cankers, whether Cytospora chrysosperma propagules are found on or in aspen bark, and if there is variation in virulence among C. chrysosperma isolates. Cankers were significantly larger on drought-stressed trees than on nonstressed trees. In the spring, wounds on drought-stressed, potted aspen trees, Populus tremuloides, were susceptible to infection by C. chrysosperma for at least 10 days after wounding. Wounds on nonstressed trees were susceptible for about 4 days. Resistance to canker initiation, as measured by the number of expanding cankers, was expressed about 7 days after wounding on stressed trees. Resistance in nonstressed trees was observed within 2 days. Cytospora was not found on asymptomatic trees as an inner bark inhabitant but was found on bark surfaces. Virulence of C. chrysosperma isolates was significantly different among isolates from 8 different hosts and 5 isolates from aspen when inoculated on aspen."