Plant growth promoting activities of rhizobacteria associated with tomato in semi-arid region

Abstract

The present investigation was designed to evaluate the plant growth promoting activities of rhizobacteria associated with tomato. Twenty six rhizosphere soil samples of tomato were randomly collected from tomato cultivating areas of district Faridabad, Haryana, India and a total of 56 strains of rhizobacteria were isolated on three different selective and non-selective medium i.e. nutrient agar, King’s B agar and glycerol-arginine agar at 300C. Pseudomonas was identified as the predominant bacterial genus with almost 34% of the isolated strains belonging to this genus. All isolated strains were evaluated for indole acetic acid (IAA) production and phosphate solubilization. In vitro IAA production was observed in 76.8% isolates and phosphate solubilizing activity was given by 41.1% isolates. Isolates varied significantly (P < 0.05) for IAA production as well as phosphate solubilization. The average IAA concentration recorded for these isolates was 6.32 μg/ml and the inorganic phosphate (Pi) released in Pikovskaya’s broth at 15 days after incubation (DAI) was 18.80 μg/ml. The average pH of Pikovskaya’s broth at fifteen DAI dropped to 5.20 from 7.00 at 0 DAI. Leading IAA producing genera were Flavobacterium and Azotobacter while maximum P-solubilization activity was shown by the genus Pseudomonas. The isolate TNAM22 gave the highest IAA concentration of 9.81 μg/ml while the isolate TKB14 released maximum Pi i.e. 22.7 μg/ml.