PLANT GROWTH PROMOTING ACTIVITIES AND TOLERANCE TRAITS AMONG AZOTOBA CTER CHROOCOCCUM STRAINS ASSOCIATED WITH SUGARCANE RHIZOSPHEREFARAH AHMAD AND IQBAL AHMADAbstract Azotobacter chroococcum strains as sod a ted with sugarcane (var. Hari Rani) rhizosphere were isolated, characterise and screened for their plant growth promoting (PGP) activities like production of indole acetic acid (IAA), ammonia, I1CN and influence on seed germination in vitro. All 10 test isolates showed typical morphological, cultural and biochemical characteristics. These strains exhibited varied level of above PGP activities. Production of high level of ammonia, IAA and FICN were detected among 54.5%, 27.3% and 18.2% strains respectively. Quantitative estimation of IAA was found in the range of 10.0 to 12.5 p,g/rril of culture filtrate. Further tolerance among these isolates to environmental factors like pH, salt, and certain heavy metals (Pb, Cd, Cu, Cr & Ni) was tested in vitro using solid medium. Majority of the isolates could tolerate 2.5% NaC1 concentration while pH tolerance ranged from 7 to 10 by all strains. Similarly tolerance to heavy metals was determined by spot inoculation technique on heavy metal supplemented medium. Higher level of minimum inhibitory concentration (MIC), 400 1g/m1 was found for Pb, Cr & Cd and 200 1.tg/m1 for Cu and Ni. However, tolerance against mercury was comparatively less as the MIC against Hg ranged between 50 to 100 tg/ml. The findings revealed that Azotobacter chroococcum strains showing higher level of plant growth promoting activity and tolerance to environmental factors may be good potential strains to be exploited in the integrated management of plant nutrients, after studying their relative efficiency in rhizospheric soil.
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