Ascospores of the Japanese pear scab fungus (Venturia nashicola Tanaka & Yamamoto) are discharged during the day

Abstract

We investigated the diurnal pattern of ascospore discharge of the Japanese pear scab fungus (Venturia nashicola Tanaka & Yamamoto) in an orchard. Ascospores of V. nashicola were mainly discharged during the day. Most ascospores were discharged from 7:00 to 19:00: 99.6% in 2001, 99.3% in 2002, and 93.8% in 2005. Because the ascospores were discharged only when the fallen diseased leaves were wet from precipitation, the wetness of these leaves is probably imperative for spore discharge. Ascospore discharge began immediately after precipitation in the daytime. When it rained at night, however, ascospore discharge did not begin until the following morning and never began immediately after precipitation. We also investigated other meteorological factors. When fallen diseased leaves were wet, the percentage of ascospore discharge was positively correlated with the amount of solar radiation and atmospheric temperature and negatively correlated with relative humidity. Ascospore discharge was interrupted by a decrease in solar radiation and atmospheric temperature and by increased relative humidity at night. This report is the first that V. nashicola discharges ascospores primarily during the day.