Evaluation of microclimatic factors affecting ascospore release ofGremmeniella abietinavar.balsamea

Abstract

The ascospore release of G. abietina var. balsamea was measured every hour for a period of 1339 hours; it was analyzed with regard to microclimatic factors, such as rain, relative humidity, air temperature, wind speed, and leaf wetness, which were also recorded on an hourly basis. The spore dispersal period started in the middle of July and ended in October, with a peak of spore release during the first 3 weeks of August. Leaf wetness measurements were best correlated with spore dispersal. Relative humidity and rain also showed a good correlation with spore dispersal but not as good as leaf wetness. Dew was not responsible for ascospores release. Mist or fog were most probably the cause of free water deposition and, as a result, the cause of spore release when no rain was recorded. Mist and fog were not measured directly but could be inferred from leaf wetness readings. Temperature had no direct effect on spore release.