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item Howell, Charles - Charlie
item DEVAY, J
item GARBER, R
item WEIR, B

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Mutants of the biocontrol fungus Trichoderma virens that are deficient for production of the phytotoxin viridiol cause much less harm to the root system of developing cotton seedlings than do preparations of the parent strains. In order to determine if this phenomenon extended to the root systems of mature plants and might result in higher stands and lint yields, field tests were conducted on seed treated with preparations made from parent and viridiol-deficient mutant strains of T. virens in California cotton fields heavily infested with seedling disease pathogens. The results showed that seed treatment with parent and mutant strains of T. virens, gave significantly higher plant stands than nontreated or chemically treated controls. Although not significant, the plants treated with biologicals also produced higher lint yields than either control. There were no significant differences between seed treated with parent or mutant strains of T. virens.

Technical Abstract: Viridiol(-) mutants of the biocontrol agent Trichoderma virens can no longer synthesize the phytotoxin viridiol, but retain the capacity to produce antifungal antibiotics, act as mycoparasites, and control cotton seedling disease incited by Rhizoctonia solani. The use of biocontrol preparations containing viridiol(-) mutants virtually eliminated the phytotoxicity associated with treatment of cotton seed with high concentrations of parent strain preparations. The phytotoxic and biocontrol activities of parent and viridiol(-) strains were compared by coating Apron treated cotton seed with a latex sticker and air-dry, finely ground, preparations of the fungi. Field tests of treated seed in plots heavily infested with seedling disease pathogens at Shafter and Dos Palos, California showed that treatment with parent or some mutant strains of T. virens gave significantly better stands than nontreated or fungicide treated controls. With the exception of one strain, all seed treated with the biocontrol agents gave higher average lint yields than the nontreated or Apron treated controls, although the differences were not significant.