Evaluation of two methods for assessing ascospore productivity of the apple scab pathogen, Venturia inaequalis

Abstract

The standard water bubbler and a modified tower aspirator for quantifying ascospore productivity were compared. Samples, each consisting of 50 discs, were cut randomly from scab-infected McIntosh apple leaf litter in the spring and 18 samples were processed by each method. The square roots of hemocytometer counts adjusted for unit area or gram dry weight of leaf samples were found to be normally distributed. More spores were harvested from the same amount of leaf material with the bubbler than with the tower. The coefficient of variation for spore yields expressed on a per area or a per gram dry weight basis was smaller for the tower method than for the bubbler, although the values were not significantly different. Where detection of low ascospore productivity is not essential, the tower method is preferable in terms of ease, speed of operation, and the potential for electronic enumeration of harvested ascospores.