Asian Journal of Microbiology, Biotechnology & Environmental Sciences Paper

POPULATION AND NITROGEN FIXATION BY AZOSPIRILLLIM SPP. ISOLATED FROM THE RHIZOSPHERE OF FOXTAIL MILLET

N. RAJYA LAKSHMI, M. MOHAMMED RAFI, K. V. BHASKARA RAO AND P. B. B. N. CHARYULU

Abstract

Growth of all organisms depends on the availability of mineral nutrients. Plants normally derive nutrients from the soil. Among all mineral nutrients, nitrogen (N) plays the most important role in augmenting agricultural production. Further, nitrogen, which is required in the greatest quantity of all mineral nutrients absorbed by plant roots, is an essential component of proteins, nucleic acids and other cellular constituents. Rhizosphere samples of many crop plants harbour several beneficial organisms which include associative nitrogen fixers. Although there are many reports on the association of these organisms with roots of many crop plants, virtually little information is available on nitrogen fixation by Azospirillum isolates from the rhizosphere of foxtail millet. Foxtail millet, a minor millet, is one of the important staple foods in semi-arid regions like Anantapur. Hence, the present study is mainly concerned with isolation and evaluation of nitrogen fixation by' Azospirillum isolates from the rhizosphere of foxtail millet [Setaria italica (L.) Beauv.]. Rhizosphere soil samples from Chitra, Lepakshi, Prasad and Srilakshmi varieties were planted to black loamy soil were used for isolation and nitrogen fixation in pot culture studies. Rhizosphere samples from 30, 45, 60 and 75-day old plants were used for isolation of Azospirillunz. Non-rhizosphere samples served as control. The population of the Azospirillum was estimated by MPN method. Nitrogen fixation by Azospirillum isolates was determined by autoanalyser (Kjeldahl method). Populations of Azospirillum were always lower in the non-rhizosphere samples when compared to the rhizosphere samples. Nitrogen fixation by the rhizosphere isolates is more when compared to the isolates from the non-rhizosphere samples. The isolates of Azospirillum varied in their nitrogen-fixing ability.