THE RELATION OF BARK MOISTURE TO THE DEVELOPMENT OF CANKER DISEASES CAUSED BY NATIVE, FACULTATIVE PARASITES: VII. SOME EFFECTS OF THE SAPROPHYTES ON THE BARK OF POPLAR AND WILLOW ON THE INCIDENCE OF HYPOXYLON CANKER

Abstract

It has been shown that saprophytes were prevalent at the nodes, lenticels, and other irregularities on 1-, 2-, and 3-year-old bark of Populus trichocarpa Torrey and Gray and Salix sp. Antagonism tests demonstrated that the extracts of natural bark and two of the most common saprophytes inhibited the growth of Hypoxylon pruinatum (Klotzsch) Cke. However, the extracts of surface-sterilized bark were found to promote the cultural growth of the pathogen. No differences were observed in the behavior of the extracts obtained from dormant and actively growing bark tissues.The results of inoculation experiments demonstrated that Hypoxylon canker did not develop when the saprophytes were present on watered greenwood cuttings of black Cottonwood and willow. However, the saprophytes were not effective in preventing infection and canker growth on cuttings with below-normal levels in bark turgor. Surface-sterilized cuttings proved susceptible to the disease at all levels of bark turgor.Possible relationships between the temperature and moisture requirements of the pathogen and representative bark antagonists, and the epidemiology of canker diseases caused by facultative parasites, are discussed.