Enzyme-Linked Immunosorbent Assay (ELISA) for Identification of Bradyrhizobium Japonicum Strain in Root Nodule of Soybean Grown in Kathmandu Valley

Abstract

ELISA technique was applied for the identification of Bradyrhizobium japonicum and to study their somatic antigen diversity. B. japonicum was isolated from the nodules of soybean grown on Tangla soil and identified. Somatic antigen of B. japonicum was prepared and immunized to New Zealand white rabbit to raise polyclonal antibody against it. Indirect ELISA was optimized and immuno cross reactivity of the strains from the different localities was observed. The optimal dilution of the antisera was found to be 1000 folds and secondary antibody to be 2000 folds. The cut off value for the colour observation at OD was 0.76nm. Mulpani strains have similar somatic antigen showing 97% cross reactivity while the Dhobighat strains shows the least cross reactivity with 19%. Cross reactivity of the strains from same locality was also not consistent. Champa singh strain show high variation up to 40% (22-62%) while Panga strains show 9% (26-34%). Different localities of the same agro climatic region possess different strain of B. japonicum as well as different nodule of single plant also gets infected by different strains.