Reduction of verticillium wilt symptoms in cotton following seed treatment with Trichoderma virens.

Strains of Trichoderma virens 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 d, plants were rated for Verticillium wilt symptoms and plant heights measured. Two strains of T. virens significantly reduced (alpha = 0.05) the disease-severity ratings in V. dahliae-inoculated plants of two cotton cultivars, Rowden and Deltapine 50. This result indicated that T. virens may induce a systemic resistance response in cotton, but concentrations of terpenoid phytoalexins in stele extracts were not significantly different in V. dahliae-inoculated plants that had been treated with the T. virens when compared with plants treated with the carrier alone. In the absence of Verticillium, plants treated with the G-4 isolate of T. virens were significantly taller than control plants treated without T. virens. This result indicates that some strains of T. virens may have growth-promoting activity.