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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1.0 g of NaNO₃ per liter, drying of the sporulation medium superseded the influence of nitrogen nutrition.