Selective isolation from soil and separation in vitro of P and Q strains of Trichoderma virens with differential media

Strains of the biocontrol fungus Trichoderma virens may be separated into P (gliovirin producing) or Q (gliotoxin producing) groups by culture of coni dial inoculum on agar media containing selective amendments. Strains of the P group will grow on PDA amended with chlorothalonil or thiabendazole, but not on PDA amended with gliotoxin or fludioxonil, and they do not inhibit the growth of Bacillus subtilis in culture. Strains of the a group will gro w on gliotoxin and fludioxonil, but not on chlorothalonil or thiabendazole, and they inhibit the growth of B. subtilis in culture. Strains of T. viren s can also be isolated from natural soil with selective media. A PDA medium containing rifampicin (50 mu g mL(-1)), chlorothalonil (1.25 mu g mL(-1)) and thiabendazole (0.6 mu g mL(-1)) can be used to selectively isolate P st rains from soil. PDA containing rifampicin (50 mu g mL(-1)), gliotoxin (50 mu g mL(-1)) and low chlorothalonil (0.75 mu g mL(-1)) will selectively iso late a strains from soil. Since P and Q strains of T. virens are known to d iffer in their biocontrol efficacy toward different soil-borne diseases, th eir separation into groups and isolation from soil on selective agar media should allow the development of more focused and efficient screening proced ures.