Eutypella Canker of Maple: Ascospore Discharge and Dissemination

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Abstract
Free moisture on mature perithecia of E. parasitica induced discharge of viable ascospores in groups of 8 (spore octads). At least 0.03 cm of rain penetrating the tree [Acer saccharum and A. rubrum] crown canopy was required to initiate discharge; high relative humidity alone was not sufficient, but did prolong the spore ejection from moist perithecia. Previous mositure content of stromata determined the magnitude of spore discharge. In the laboratory, spores were discharged from moistened perithecia at 4-36.degree. 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.degree. C for 72 wk did not adversely affect spore discharge or germination. Ascospore octads were trapped with a Hirst spore trap with Rotorod samplers 25 m downwind from maple cankers in a mixed hardwood stand in northern Wisconsin [USA]. The number of spores trapped decreased rapidly with increasing distance from the source. The general dispersal pattern depended on wind direction, but was modified by updrafts and other types of turbulence within the stand.

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