Verticillium tricorpus, a non-pathogenic fungus to cotton, exhibits a sustained biological activity against Rhizootonia damping-off of cotton seedlings in both greenhouse and field trials. For two successive years, 1988 and 1989, V. tricopus was tested as biocontrol agent under field conditions. Experimental field plots at Shafter and Los Banos, CA, which were naturally infested with seed and seedling pathogens and with V. dahliae, were preplant treated with a sand:cornmeal mixture (95:5 v/v) which had been colonized by selected isolates of V. tricorpus. The inoculum was worked into the seed row approximately two weeks before planting. One month old cotton seedlings were randomly sampled and the roots were plated on a selective agar medium to determine the rhizosphere competence of the isolates of V. tricorpus.

The results from these tests showed that V. tricorpus successfully colonized the roots of the you 9 cotton seedlings. The antagonist gave protection against damping-off caused by Rhizoetonia solani as good as one of the best chemical seed treatment (Chloroneb, 1,4 dichlor-2,4-dimethoxy-benzene). In one case (Shafter) in 1989, it increased the percentage seedling survival compared with the untreated control by 15% (P=0.05). This resulted in an increase of cotton lint by 250 lbs per acre.

During 1988 and 1989, the biological activity of V. tricorpus as a biocontrol of Verticillium wilt on cotton was also monitored at the above locations. In 1988, there was a continual trend through the season of less wilt in the biocontrol plots which was more evident in 1989. It resulted in a 14% reduction of foliar symptoms that was statistically significant (P=0.05), when compared with the control plots.

Additionally, observations in greenhouse trials have shown biocontrol activity of V. tricorpus against Rhizoctonia damping-off of Red Kidney bean. This widens the possible use of V. tricorpus as a biocontrol for damping-off of bean seedlings.

Current research is now focused on the biochemical mode of action of V. tricorpus in the biological control of R. solani. Initial observations indicate that the interactions of the host and the pathogen and pathogenesis may involve regulation of oxidative enzymes. The final goal will be to understand the mechanism of biological control and to enhance the biocontrol activity of V. tricorpus.