investigation on biological control of sugar beet damping-off disease by some isolates of trichoderma harizanum rafai

due to high antagonistic activity of trichoderma harizanum, 5 isolates t.h.k, t.h.bi, t.h.mo, var33 and torbat vi were selected and their efficacy was studied for controlling sugar beet damping-off caused by rhizoctonia solani, under in vitro and in vivo conditions.  antagonistic ability of t. harzianum isolates was investigated as dual culture on pda in concomitant and sequential cultures, 48 and 96 hours after r. solani culturing.  it was found that all t. harzianum isolates colonized r. solani colony, stopped its mycelial growth and sporulated on it.  in all 3 experiments, the isolate t.h.k, colonized r.solani colony in a shorter time compared to other isolates.  microscopic observations showed that these isolates coiled around, penetrated and degenerated hypha of r.solani, stopped its growth and finally lysed it.  volatile metabolites of t. harzianum isolates had significant inhibitory effect on mycelial growth of the pathogen, among which t.h.bi isolate with inhibition percent of  89.63% had the best effect.  in investigation of inhibitory effect of 5 concentrations (% 10-% 15-% 20-% 25-% 30) of culture filtrates of t. harzianum isolates in reduction of r. solani mycelial growth, it was found that none of the isolates at the above concentrations had any effect on r. solani mycelial growth. in greenhouse experiments, it was cleared found that seed coating or soil drenching by antagonistic agents had significant effect in reduction of seedling mortality, 30 days after sowing in comparison with infected control and there were significant differences among the isolates.  isolates t.h.k and var33 in soil drenching method, had the best effect in controlling of the disease.