Aluminum-tolerant strains of azospirillum brasilense and their associative nitrogen fixation with finger millet (eleusine coracana) genotypes in an acid soil

Abstract

Aluminum-tolerant (adapted) strains Alr-1, Alr-2, Alr-3 and Alr-4 of Azospirillum brasilense RAU 3051 (from an acid soil) were isolated through step-wise transfer to higher levels of aluminum. One of the strains (Alr-3) showed more growth and greater nitrogenase activity at low pH and in 100/xg AlCl3ml_1 than parental and other Al-tolerant strains. These tolerant strains also showed cross-resistant to neomycin but not to streptomycin except Alr-1. Aluminum-adapted strains also tolerated elevated levels of manganese (75-130pg MnCl2ml_1). It has been demonstrated that the response of inoculation with Al-adapted strains was variable with different genotypes of finger millet in an acid soil. An initial low level of nitrogen was essential for maximum associative N2 fixation and grain and straw yield. Also it appears that acid-adapted strains may be most suitable for nitrogen economy in acid soils having various pH and associated factors of acidity. © 1991, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.