ABSTRACT

Attempts were made to isolate, characterize and evaluate the effect of native isolates of Azotobacter on growth of maize at Department of Microbiology, UAS, Dharwad. A total of 50 Azotobacter isolates were obtained from rhizosphere soils of maize and sorghum crops grown in Gadag and Dharwad districts of Karnataka. All isolates were subjected for morphological, functional and biochemical characterization. Among 50 isolates, 49 were cocci in shape and all the isolates were Gram negative. The isolates exhibited varying pigmentation viz., brown, light yellow, yellow and yellowish-green. Majority of the isolates produced brown pigmentation. Among 50 isolates, 38 were positive for cyst formation. The amount of nitrogen fixed by the isolates ranged from 2.12-9.95 mg N2/g of ‘C’. The native isolate NMAz5 fixed the highest amount of nitrogen (9.89 mg N2/g of ‘C’). While, all the isolates produced both IAA and GA. The amount of IAA and GA production ranged from 2.68 to 42.86 µg/ml and 1.79-17.51 µg/25 ml respectively. The amount of Pi and K released ranged from 3.53-11.73 µg/ml and 3.51-17.10 µg/ml respectively. Biochemical characterization, indicated that isolates were positive for catalase, oxidase, citrate utilization and ammonia production but negative for methyl red, indole test and nitrate reduction test. These three potent isolates viz., NMAz5, DSAz26 and YSAz44 were further evaluated for their potential in enhancing the growth parameters of maize viz., plant height, number of leaves, stem girth, shoot and root dry weight, total dry matter production, soil dehydrogenase activity and nutrient concentration of maize plants. Seed inoculation with consortium of these three Azotobacter isolates with 75 % RDF significantly enhanced all the growth parameters and nutrient concentration of maize compared to uninoculated treatments. Hence, these need to be further tested under field conditions in order to initiate their use in biofertilizer/ bioinoculant production.