Combination of Trichoderma species and Bradyrhizobium japonicum in control of Phytophthora sojae and soybean growth

Soybean, Glycine max (L.) Merr is one of the most important oilseed plants in the world and Phythophthora root and crown rot is a significant limiting factor for its planting. In the present study the antagonistic effect of 12 Trichoderma spp. in vitro and these Trichoderma spp. in combination with Bradyrhizobium japonicum in vivo on Phytophthora sojae and soybean growth were tested. In laboratory tests the effects of Trichoderma isolates were studied in dual culture, volatile compounds and culture filtrate metabolites. The most hyphal growth inhibitions were obtained using T. virens, T. orientals and T. brevicompactum in dual culture tests and T. atroviride in volatile compounds test. The effects of Trichoderma culture filtrates on P. sojae hyphal growth were studied at six concentrations in CMA medium and the results showed that culture filtrates of all species inhibited the hyphal growth and that different concentrations had different inhibitory effects. The most inhibition was obtained by T. virens and T. brevicampactom culture filtrates. The greenhouse tests were carried out as two experiments. In the first experiment the effects of coated seeds with Trichoderma isolates and B. japonicum, alone and in combinations, on control of P. sojae and in the second experiment the effect of these two biocontrol agents on soybean growth, alone and in combinations, were assayed. In the first experiment, germination percentage, damping-off, seedling vigour index (SVI) and disease severity were measured and results showed that T. brevicompactum as alone and in combinations, was the most effective species. In the second experiment, coated seeds with Trichoderma isolates and B. japonicum, as alone and in combinations, significantly promoted the growth of treated seeds and the most effective species were T. orientals, T. brevicompactum and T. spirale. Hence, results indicate that T. brevicompactum, as the second most common species after T. harzianum in Iran, was the most successful species applied individually and in combinations with B. japonicum to act as biocontrol agent for P. sojae and was also able to promote plant growth.