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Environmental Factors Influencing the Formation of Basidia and Basidiospores in Thanatephorus cucumeris. Gerard C. Adams, Jr., Research assistant, Department of Plant Pathology, University of California, Davis 95616; Edward E. Butler, professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 73:152-155. Accepted for publication 16 June 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-152.

Isolates of Thanatephorus cucumeris, anastomosis group (AG) AG-1 and AG-4, each capable of sporulation on agar media, were grown in different environments. The influence of aeration, relative humidity (RH), carbon dioxide (CO2) concentration, and substrate drying on formation of basidia and basidiospores was analyzed. Fruiting occurred in 3-L chambers, containing 15 cultures each in a 15 100-mm petri plate, only when ventilation was adequate. Isolates of AG-1 formed basidia when air (99% RH) circulated through chambers at 20 L/hr while AG-4 isolates required 45 L/hr. Incubating cultures in the presence of alkali and in CO2-enriched environments suggested that the accumulation of respiratory CO2 within chambers receiving air flow rates <45 L/hr inhibited fruiting. Isolates of AG-1 formed basidia at 0.06%, but not at 0.10%, CO2 while AG-4 isolates did not form basidia at CO2 concentrations above 0.03%. Incubation of cultures in different relative humidities had little effect on fruiting unless low RH caused agar medium to visibly shrink from evaporative loss of water. Isolates of AG-1 were stimulated to produce abundant basidia by slow drying of the sporulation medium while AG-4 isolates were unaffected. Although isolates of AG-1 usually did not produce basidia after growth on media containing <1.0 g of NaNO3 per liter, drying of the sporulation medium superseded the influence of nitrogen nutrition.