Abstract

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 a-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.

Key words: Proline content, drought, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, plant growth promoting bacteria, phenolics content, indole acetic acid (IAA).