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| مجله علوم کشاورزی ایران | ||
| Article 13, Volume 37, Issue 7 - Serial Number 1482, June 2006 PDF (257.3 K) | ||
| Abstract | ||
| This study was conducted to evaluate the ability of a total of 158 bacteria isolates collected from soybean rhizosphere against soybean damping-off disease caused by Phytophthora sojae, using the dual culture method. Sixty-six strains were identified as Gram positive, 80 isolates as fluorescent pseudomonads and 12 isolates as Gram negative. Among these bacteria, a total of 100 strains that caused growth inhibition zone of 3 mm or more against P. Sojae were chosen for greenhouse studies to control damping-off. Each experiment was conducted in a factorial trial with two factors representing soil and seed treatments. Results revealed that isolates B3, B80, B12, B43, B51, B63, and B64, using either application method, displayed effects similar to or higher than Ridomil fungicide in reducing the disease percentage. In soil treatment method, isolates B3, and B43, caused 70.84% reduction in damping-off whereas B63, and B51, 54.34%. Isolates B12, B80, and B64 exhibited 66.67, 54.17, and 50% decline in disease development, respectively. In seed treatment method, isolates B43, B51, and B63 reduced damping-off by 50%; whereas B3, B12, B80, and B64 caused 62.5, 58.34, 45.84, and 37.5% decrease in disease occurrence, respectively. Application method had different effects on disease suppression.B3 and B12 isolates applied as soil treatment had a significantly higher disease control effect as compared to seed treatment. B43, B63, B51, B80, and B64 strains produced similar effects in reducing damping-off, regardles of the application method employed. Regression analysis showed a high degree of correlation between soybean root colonization ability by antagonists and disease control in the two application methods used. Bacteriological tests identified B3, B12, and B80 as Bacillus spp., whereas B43, B51, B63, and B64 were fluorescent Pseudomonas spp. In determining the effects of volatile metabolites produced by antagonistic bacteria on fungal growth, it was found that all three Bacillus strains inhibited mycelial growth of Phytophthora sojae in vitro. The culture media, PDA and NA containing 2% (w/v) glucose, influenced the inhibitory activities of Bacillus strains. Culture filtrate of individual Bacillus isolates inhibited mycelial growth of P. sojae in Petri dishes. All four fluorescent pseudomonads generated antibiotic compounds as well as volatile metabolites that caused a significant inhibition of mycelial growth of P. sojae. B43 and B63 isolates produced siderophore activity on King’s B medium. In studying hydrogen cyanide production by antagonists, only Pseudomonas strains were positive producers. Non of the Bacillus isolates produced any HCN. The bacterial colonization experiment showed that B3, B12, B63, B43, B51, B80, and B64 isolates increased their populations on soybean root system by 814, 771, 703, 700, 694, 655 and 541 folds, respectively. | ||
| Keywords | ||
| Bacillus; Phytophthora sojae; Pseudomonas; soybean | ||
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