RESUMEN
In the present study attempts have been made to characterize urease expression in slow growing Bradyrhizobium strains TAL442 and MO5 which are endosymbionts of green gram (Vigna radiata (L.)Wilczek). It was found that urease activity in vegetative cells of both the strains was inducible unlike their fast growing counterparts. Mode of regulation in TAL442 was governed by presence of ammonia. Urease expression was also detectable in bacteroids of both the strains which was not influenced by presence of external nickel chloride in high concentration, a situation detrimental to the vegetative cells.
RESUMEN
A total of 354 indigenous bradyrhizobia were isolated from soybean nodules collected from five major crop grown regions. Host-specific 12 phages, each active on particular strains were selected. Factors, which influence the interaction between the host and phage, were examined. Four different types of plaques were detected. Nearly 17% of isolates were found resistant to all phages. Phage sensitivity patterns revealed a total of 32 distinct phage genotype groups. Different set of phage combinations expressed variation in specificity for parasitizing against particular group of rhizobia. Distributions of isolates in each phage types differed markedly between regions. Interestingly, nine strains belonging to phage group 16 exhibited high ex planta nitrogenase activity in culture. However, no correlation could be established between high ex planta nitrogenase activity and their symbiotic effectiveness with soybean cultivars. Soybean cv. JS335 showed relatively superior performance than Bragg and Lee with indigenous bradyrhizobial strains. Phage typing revealed the existence of large genetic diversity among native rhizobia and selection of the superior bradyrhizobial strains can also be possible for a given soil-climate-cultivar complex.