The use of Rhizobium inoculant for groundnut is a common practice in India. Also, co-inoculation of Rhizobium with other plant growth-promoting bacteria received considerable attention in legume growth promotion. Hence, in the present study we investigated effects of co-inoculating the sulfur (S)-oxidizing bacterial strains with Rhizobium, a strain that had no S-oxidizing potential in groundnut. Chemolithotrophic S-oxidizing bacterial isolates from different sources by enrichment isolation technique included three autotrophic (LCH, SWA5 and SWA4) and one heterotrophic (SGA6) strains. All the four isolates decreased the pH of the growth medium through oxidation of elemental S to sulfuric acid. Characterization revealed that these isolates tentatively placed into the genus Thiobacillus. Clay-based pellet formulation (2.5 x 10(7) cf ug(-1) pellet) of the Thiobacillus strains were developed and their efficiency to promote plant growth was tested in groundnut under pot culture and field conditions with S-deficit soil. Experiments in pot culture yielded promising results on groundnut increasing the plant biomass, nodule number and dry weight, and pod yield. Co-inoculation of Thiobacillus sp. strain LCH (applied at 60 kg ha(-1)) with Rhizobium under field condition recorded significantly higher nodule number, nodule dry weight and plant biomass 136.9 plant(-1), 740.0mg plant(-1) and 15.0 g plant(-1), respectively, on 80 days after sowing and enhanced the pod yield by 18%. Also inoculation of S-oxidizing bacteria increased the soil available S from 7.4 to 8.43 kg ha(-1). These results suggest that inoculation of S-oxidizing bacteria along with rhizobia results in synergistic interactions promoting the yield and oil content of groundnut, in S-deficit soils.

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Phyllosphere bacteria plays important role in mitigating biotic and abiotic stress. This study aimed to use phyllosphere bacterium of rice to enhance drought tolerance. Bacterial isolates obtained from rice phyllosphere were investigated for their plant growth promoting activities and role in alleviation of drought stress in rice. The isolates were identified as Bacillus altitudinis FD48, Bacillus pumilus FS20 and Bacillus aquimaris MD02 based on 16S rRNA gene sequence. B. altitudinis FD48 was found to produce indole acetic acid (IAA) (2.82 µg/ml) compared to other two isolates even under PEG induced drought conditions. However, under normal conditions, B. altitudinis FD48 produced 8.0 µg/ml. Quantitative estimation of 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity was found to be 192 n moles -ketobutyrate mg -1 h -1 and positive for accD gene. B. altitudinis FD48 increased the root and shoot length of rice under in vitro conditions and also improved the germination percentage of rice seeds at different concentration of PEG 6000. Inoculation of rice with plant growth promoting, drought tolerant B. altitudinis FD48 increased relative water content, chlorophyll stability index and membrane stability index compared to control (uninoculated plants) when the plants were subjected to drought by discontinuing water for 8 days after 30 days of germination. Similarly, rice treated with B. altitudinis increased proline content, phenolics content, catalase activity and reduced malondialdehyde (MDA) content in plants. Ethylene emission was significantly reduced by B. altitudinis FD48 inoculation under drought condition when compared with control. This study suggests that the isolate B. altitudinis FD48 may be used at field level to mitigate drought stress in rice.

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