VIEW ARTICLE

Ecology and Epidemiology

Eutypella Canker of Maple: Ascospore Discharge and Dissemination. David W. Johnson, Plant pathologist, U.S. Forest Service, U.S. Department of Agriculture, Denver, CO 80225; James E. Kuntz, professor, Departments of Plant Pathology and Forestry, University of Wisconsin, Madison, 53706. Phytopathology 69:130-135. Accepted for publication 30 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-130.

Free moisture on mature perithecia of Eutypella parasitica induced discharge of viable ascospores in groups of eight (spore octads). At least 0.03 cm of rain penetrating the tree crown canopy was required to initiate discharge; high relative humidity alone was not sufficient, but did prolong the spore ejection from moist perithecia. Previous moisture content of stromata determined the magnitude of spore discharge. In the laboratory, spores were discharged from moistened perithecia at 4–36 C. Discharge from perithecia under controlled laboratory conditions resembled that observed in the field. Stromata collected during any season ejected spores when bark was moistened. Storage of stromata at –24 C for 72 wk did not affect spore discharge or germination adversely. Ascospore octads were trapped with a Hirst spore trap and with Rotorod samplers 25 m downwind from maple cankers in a mixed hardwood stand in northern Wisconsin. The number of spores trapped decreased rapidly with increasing distance from the source. The general dispersal pattern depended upon wind direction, but was modified by updrafts and other types of turbulence within the stand.