VIEW ARTICLE

Ecology and Epidemiology

Environmental Factors Affecting Survival of Ascospores of Sclerotinia sclerotiorum. A. J. Caesar, Graduate research assistant, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; R. C. Pearson, associate professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 73:1024-1030. Accepted for publication 11 February 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1024.

Laboratory studies showed that temperatures of 25 C or greater combined with relative humidities in excess of 35% were most detrimental to Sclerotinia sclerotiorum ascospore survival. Generally, ascospore mortality increased as temperature and relative humidity increased. Temperature correlated most closely with ascospore mortality on the topmost leaves of the bean (Phaseolus vulgaris) canopy in field studies. Ascospore mortality on the topmost leaves during a 48-hr period was significantly positively correlated with the number of hours at or above 21.1 C during the same period (r = 0.678 in 1980 and r = 0.766 in 1981). Ascospore survival on shaded leaves ~12- 15 cm above ground within a dense canopy averaged 21.5% greater than on topmost leaves. Few ascospores survived on topmost leaves after 6 days in the field, with ascospore viability ranging from 7 to 0% after 6 and 14 days, respectively. Shelters of plastic films differentially transmissive of ultraviolet (UV) radiation significantly reduced ascospore mortality on bean leaves in the field. After 224 hr of irradiation with two FS-40 Sunlamp tubes in the laboratory, ascospore survival was 49.0 and 13.4% under plastic films that transmitted 10 and 50- 60% UV radiation in the 300- 400 nm range, respectively.