African Journal of Biotechnology Vol. 5 (10), pp. 842-845, 16 May 2006   

ISSN 1684–5315 © 2006 Academic Journals        

Full Length Research Paper

Symbiotic effectiveness of acid-tolerant Bradyrhizobium strains with soybean in low pH soil

C. APPUNU* and B. DHAR

Microbial Genetics Laboratory, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi-221005, INDIA

*Corresponding author. E-mail: cappunu@yahoo.com. Tel: 0542-2307123. Cell: 00 91 9838732564. Fax: 0542-2368174.

Accepted 23 March, 2006

Abstract

Eight acid tolerant strains of Bradyrhizobium isolated from soybean plants grown on acid soils in Madhya Pradesh, India, were examined for their ability to survive in soil and YEMB at low pH levels. All the tested isolates survived in acidic (pH 4 -6) conditions and their survival capacity was higher in soil than in nutrient medium at same levels of low pH. Variation among different strains showed that there is potential to improve strain performance under stress conditions. Further, symbiotic effectiveness of these strains was determined under the polyhouse conditions in sterilized soil (pH 4.5). Highest and lowest symbiotic characters, dry matter production and nitrogen improvement per plant were observed in PSR001 and NSR008 inoculated plants, respectively. All the examined isolates showed considerable variability in their symbiotic performance. The strain found to be more tolerant to stress were more effective N₂ fixers in symbiosis with soybean in acid-soil conditions. 

Key words: Symbiotic effectiveness, Bradyrhizobium strains, pH, soybean.