Phylogenetic analysis of 23S rRNA gene sequences of some Rhizobium leguminosarum isolates and their tolerance to drought

Biochemical, functional and molecular characterization of pigeon pea rhizobia isolated from semi-arid regions of India

Pigeon pea (Cajanus cajan (L.) Millspaugh) is among the top ten legumes grown globally not only having high tolerance to environmental stresses along, but also has the high biomass and productivity with optimal nutritional profiles. In the present study, 55 isolates of rhizobia were identified from 22 nodule samples of pigeon pea collected from semi-arid regions of India on the basis of morphological, biochemical, plant growth promoting activities and their ability to tolerate the stress conditions viz. pH, salt, temperature and drought stress. Amongst all the 55 isolates, 37 isolates showed effective nodulation under in vitro conditions in pigeon pea. Further, five isolates having multiple PGP activities and high in vitro symbiotic efficiency were subjected to 16S rRNA sequencing and confirmed their identities as Rhizobium, Mesorhizobium, Sinorhizobium sp. Further these 37 isolates were characterized at molecular level using ARDRA and revealed significant molecular diversity. Based on UPGMA clustering analysis, these isolates showed significant molecular diversity. The high degree of molecular diversity is due to mixed cropping of legumes in the region. The assessment of genetic diversity and molecular characterization of novel strains is a very important tool for the replacement of ineffective rhizobial strains with the efficient strains for the improvement in the nodulation and pigeon pea quality. The pigeon pea isolates with multiple PGPR activities could be further used for commercial production.

Molecular Diversity Analysis of Plant Growth Promoting Rhizobium Isolated from Groundnut and Evaluation of Their Field Efficacy

Rhizobium are nitrogen-fixing bacteria which possess the nif gene that codes for the nitrogenase enzyme involved in the reduction of atmospheric dinitrogen (N₂) to ammonia. Thirty rhizobial strains were identified from ten groundnut plant root nodules collected from semi-arid regions of Rajasthan, India. The isolates were initially identified on the basis of morphological, biochemical, and molecular characteristics. These rhizobium strains were further screened for plant growth promoting activities. Twenty-eight strains were able to produce indole acetic acid, nine strains could solubilize phosphate, and twenty-nine strains exhibited positive results for siderophore and ammonia production. All the bacterial strains were able to efficiently nodulate the groundnut under pot conditions and based on multiple PGP activities six strains were selected for field evaluation. Field experiments confirmed the effectiveness of these selected rhizobium strains resulted in significantly higher nodule number, nodule dry weight, grain yield, and yield components of inoculated plants. Inoculation of the rhizobium strain GN223 followed by GN221 resulted in high yield and field efficiency. Isolation of effective microbial strains is the prerequisite to increase the yield which is evident from the field data of the present study. Hence, these strains might serve as proficient inoculants.