Differential symbiotic response of phage-typed strains of Bradyrhizobium japonicum with soybean cultivars.

In this study, native Bradyrhizobium strains were isolated from the host plant, Glycine max, harvested from fields in Madhya Pradesh, India, and were typed by lytic rhizobiophages. Eight indigenous (Soy2, ASR011, ASR031, ASR032, MSR091, ISR050, ISR076 and ISR078) and two exotic strains (USDA123 and CB1809), all of which evidenced a distinct reaction with six phages, were employed in this study. The symbiotic interaction of these strains was studied initially using soybean cultivar JS335 in a sand culture in a controlled environment, and the efficiency was assessed based on the nodule number, nodule dry weight, plant dry weight, nitrogenase activity, and total accumulation of N per plant. Symbiotic effectiveness was found to be highest with the native phage-sensitive isolate ASR011, whereas it was at a minimum with the phage-resistant isolates, ISR050 and ISR078. Additionally, the effectiveness of these strains was evaluated using six soybean cultivars belonging to different maturity groups; namely, Bragg, Lee, Pusa20, PK416, JS335 and NRC37. Analysis of variance data evidenced significant differences due to both symbionts, for the majority of the tested parameters. The CB1809, USDA123, and ASR011 strains evidenced relatively superior symbiotic effectiveness with soybean cultivars Bragg, Lee and JS335. Strain ISR078 evidenced no significant responses with any of the cultivars. The ASR031 strain performed moderately well with all tested cultivars. The symbiotic response of all the strains was quite poor with cultivar PK416. Our studies showed that a significant relationship existed between the phage sensitivity and symbiotic efficiency of the bacterial strains with the host-cultivars.