SYMBIOTIC DIVERSITY AMONG ACID-TOLERANT BRADYRHIZOBIAL ISOLATES WITH COWPEA

Abstract

A total of eight acid tolerant strains of bradyrhizobia isolates from indigenous cowpea plants grown in acid soil in Varanasi, Uttar Pradesh, India, were examined for their ability to survive in soil and yeast extract mannitol broth at low pH levels. All these isolates survived in acidic (pH 3.5-6.5) conditions. Survival capacity of rhizobia was higher in soil than in nutrient medium at low pH 3.5-6.5 levels. Symbiotic effectiveness of these strains under polyhouse conditions in sterilized soil of pH 4.5 recorded the highest and lowest symbiotic characters for dry matter production and nitrogen improvement per plant in CR09 and CR20 inoculated plants, respectively. All the examined isolates showed variability in their symbiotic performances. The strain found to be more tolerant to stress were more effective N2 fixers in symbiosis with cowpea cv. Paiyur1 under acid-soil conditions. Symbiotic variation among different strains showed that there is potential to improve strain performance under stress conditions.