Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: January 12, 1996
Publication Date: N/A
Technical Abstract: Phytotoxin (viridiol) production by Trichoderma (Gliocladium) virens is thought to be a limiting factor in seed treatment for disease control. In order to test this hypothesis and obtain more effective biocontrol strains, mutants, putatively deficient in viridiol production, were made by irradiating T. virens conidia with 254 nm UV light for 55 seconds. The survivors were incubated for 5 days on PDA containing 0.25 ug ml-1 of the sterol-inhibiting fungicide flusilazole (NUSTAR). Mutants, which produced diffuse and spreading colonies, were transferred to a liquid medium containing 5% ground millet and 1% ground peat moss and shake incubated for 4 days. After harvest, the culture filtrates were extracted with chloform and the extracts were fractionated via TLC and analyzed by HPLC. Approximately 20% of the mutants trans- ferred from assay plates were deficient for viridiol production, while maintaining production of gliotoxin and viridin. When mutant strains were compared to the parent for efficacy against soreshim incited by Rhizoctonia solani, many mutants showed reduced biocontrol activity. However, some showed activity equivalent to that of the parent strains. Furthermore, suppression of viridiol production in mutant strains virtually eliminated the phytotoxicity to cotton radicles exhibited by parent strains, although some delay in root development was noted when compared to nontreated control seedlings. The use of viridiol- deficient mutants of T. virens to treat cotton seed should result in seedling disease control without adverse phytotoxic effects on the developing root system.