Selective Isolation and Enumeration of Gliocladium virens and G. roseum from Soil. Yong- Ha Park, Former Graduate Research Assistant, Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843-2132. James P. Stack, and Charles M. Kenerley. Former Assistant Professor, and Associate Professor, Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843-2132. Plant Dis. 76:230-235. Accepted for publication 8 September 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0230.

Selective media were developed for the isolation and enumeration of Gliocladium virens and G. roseum from soil. The basic antibiotic medium consisted of 3.0 g of glucose, 0.2 g of MgSO₄·7H₂O, 1.0 g of K₂HPO₄, 0.5 g of KCl, 1.0 g of NaNO₃, 0.01 g of FeSO₄ · 7H₂O, 50 mg of chloramphenicol, 50 mg of rose bengal, 50 mg of streptomycin sulfate, 500 μg of benomyl (50WP), 500 mg of sodium propionate, and 20 g of Bacto agar in 1 L of distilled water. The medium was adjusted to pH 6.0 with 25% phosphoric acid before autoclaving. By the dilution plate method, selective isolation of G. virens or G. roseum was achieved from natural soil infested with Rhizoctonia solani, Fusarium oxysporum f. sp. vasinfectum, and Pythium ultimum either by adding 20 mg of gliotoxin (a secondary metabolite of G. virens) or 1.0 mg of gliotoxin, 20 mg of pentachloronitrobenzene (75WP), and 60 mg of acriflavine to 1 L of basic antibiotic medium, respectively. At 3 days after plating, selective isolation and quantification of G. virens was achieved on the selective medium for G. virens (GVSM). From nonsterile soil infested with the strains of G. virens, recovery of four gliotoxin-producing strains of G. virens on GVSM was significantly greater than or equal to recovery on three other media that have been used to isolate G. virens. However, these previously developed media did not discriminate G. virens from other fungi, including Trichoderma spp. Recovery of two non-gliotoxin-producing strains of G. virens was lower on GVSM than on other media tested. Total colony-forming units of G. virens from three natural soils was significantly higher on GVSM than on other media tested. At 4 days after dilution plating, selective isolation of G. roseum was achieved on the selective medium for G. roseum (GRSM). Recovery of five strains of G. roseum on GRSM was higher than or equal to the recovery on another medium that has been used to isolate G. roseum.