defense responses of cotton to trichoderma spp. and its influence in control of seedling damping-off by rhizoctonia solani

damping-off of seedling is a major disease of cotton in iran. disease may become epidemic in soil with low temperature and high moisture if seed treatment isn’t done. recently, trichoderma spp. are considered as one of the biological control methods of seedling damping-off. one proposed mechanism for biocontrol in trichoderma spp. is stimulation of host defense responses and induction of resistance.in this survey, antagonistic effect of trichoderma spp. on rhizoctonia solani were studied using dual culture test. nine isolate were selected for greenhouse studies. results showed that trichoderma virens isolate a224 and trichoderma harzianum isolate a291 had maximum biocontrol effect on seedling damping-off. both isolates increased weight of seedling radicles too. isolate a224 and isolate a229 were applied on enzyme activity in germinator. experiments were conducted factorial in completely randomized design with 4 replications. peroxidase, β- 1,3 glucanse activity and total phenolic compounds levels were evaluated by colorimetic. experiments indicated that maximum level of peroxidase activity is induced 12 days after planting and maximum level of peroxidase activity is induced 10 days after planting. trichoderma isolates and rhizoctonia solani individually increased peroxidase, β- 1,3 glucanase activity and total phenolic compounds levels, but they are more pronounced and more persistent in the case of applying of combination of two fungi(trichoderma and rhizoctonia) in comparision to the control.