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item Hanson, Linda

Submitted to: Proceedings of the Joint Regional Biocontrol Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/29/2000
Publication Date: 10/1/2001
Citation: Hanson, L.E. 2001. Evidence for induced resistance to verticillium wilt in cotton by trichoderm virens seed treatment. Proceedings of the Joint Regional Biocontrol Conference.

Interpretive Summary: The mode of action of Trichoderma virens in the biological control of fungal diseases of cotton and other crops is not fully understood. A better understanding of how biological control strains act could allow for improved application of the biological control agent and might allow the use of a single strain to control multiple diseases. Strains of the biological control fungus, Trichoderma virens that control cotton seedling diseases were tested for their ability to induce resistance to verticillium wilt in cotton. Plants treated with the biocontrol agent had reduced disease. This occurred with different fungal strains and different cotton cultivars. The response was found in tissues isolated from the biocontrol agent, suggesting an induced resistance in the plant. This resistance was not related to increases in defense-related materials such as phytoalexins or tannins. While one of the biological control strains used gave some evidence of growth promotion, the other did not, indicating that the disease reduction was not due to growth promotion. Thus it appears that Trichoderma virens strains can be used to control both seedling diseases and wilts in more mature plants with a single seed treatment. Tests are ongoing to confirm this disease control activity in the field.

Technical Abstract: Trichoderma virens strains that control damping-off of cotton seedlings caused by either Pythium ultimum or Rhizoctonia solani were tested for their ability to induce resistance to Verticillium wilt. Cotton seeds were treated with dried preparations of T. virens and planted in field soil. Plants with six true leaves were inoculated with Verticillium dahliae by stem puncture. After 10 days, plants were rated for Verticillium wilt symptoms. Two strains of T. virens significantly reduced (alpha = 0.05) the disease severity ratings in Verticillium dahliae inoculated plants of two cotton cultivars, Rowden and Deltapine 50. This indicated that T. virens might induce a systemic resistance response in cotton. Concentration of terpenoid phytoalexins and tannins in stele extracts were not significantly different in plants inoculated with V. dahliae that had been treated with the T. virens than in plants treated with the carrier alone. Plants treated with one of the T. virens strains were significantly taller than the controls, but since plants treated with the other strain were not significantly taller, growth promotion does not appear to be the mechanism for disease reduction. In the first year of field tests, no treatments gave significantly different disease levels, probably due to unfavorable weather conditions for disease development.