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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.

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Stem rot with the causal agent Sclerotium rolfsii is a major disease of peanut in Guilan province, Iran. The aim of this investigation was to determine the inhibitory effect of native isolates of peanut root nodulating symbiotic bacteria on this fungus based on in vitro and in vivo studies. Several bacterial strains were isolated and purified from peanut roots collected from different fields. Eight of them were detected as the main symbiotic nodulating strains. These eight isolates were identified as Bradyrhizobium based on 16S rDNA gene analysis and different biochemical tests. The inhibitory effect of these strains on the radial growth of S. rolfsii was studied in vitro using sealed plate and dual culture methods. Strains significantly inhibited radial growth of the fungus on the PDA medium. Br9, Br18 and Br16 were recognized as strong inhibitors and Br14 as weak strain in dual culture method and used in greenhouse experiments. Ability of the selected strains in controlling the stem rot disease, reducing the disease parameters and enhancing the peanut growth parameters was investigated in greenhouse conditions. The strains significantly decreased the white rot index and increased peanut dry matter (P ≤ 0.01) in greenhouse.
 

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An experiment was conducted at Assossa Agricultural Research Center (AARC) station during 2008 cropping season in order to study the effects of co-inoculation of Bradyrhizobium japonicum (TAL-378 and TAL-379) and phosphate-solubilizing bacteria (PSB) (Pseudomonas spp.), and conventional farmers’ fertilizer level (combined and individual application of 46N kg ha-1 and 46 P2O5 kg ha-1) on nodulation, seed yield and yield components of soybean (Glycine max L. (Merr.)). Analyses of variance indicated that most of the parameters measured were significantly (P>0.05) affected by the treatments. Accordingly, dual inoculation with TAL-378 and PSB significantly increased plant height at harvest, number of nodules per plant, nodule volume per plant, nodule fresh weight per plant, and shoot height at late flowering and early pod setting compared to the other treatments. Similarly, co-inoculation with TAL-378 and PSB, and dual fertilization of nitrogen (N) and phosphorus (P) fertilizers significantly increased number of pods per plant, number of seeds per pod per plant and seed yield ha-1 compared to the other treatments. Analysis of plant tissue also indicated that dual inoculation of TAL-379 and PSB yielded the highest total N whereas the lowest was recorded for the negative control. Likewise, dual inoculation with TAL-378 and PSB and the positive control gave the highest plant P compared to all other treatments. The data revealed that, there was no significant difference (P>0.05) in days required for emergence, flower bearing and maturity, number of seeds per pod, 300 seeds weight and root length among the investigated treatments. Thus, the dual inoculation of TAL-378 and PSB is recommended to achieve maximum seed yield of soybean in Assossa area.