Spore associated bacteria of arbuscular mycorrhizal fungi improve maize tolerance to salinity by reducing ethylene stress level

The role of spore associated bacteria of arbuscular mycorrhizal fungi (AMF) in improving plant growth and alleviating salt stress is a potential area to explore. In the present study, 22 bacteria isolated from the spore walls of AMF were identified to contain 1-aminocyclopropane-1-carboxylate deaminase. These were tested for their ability to improve seed germination and alleviate salt stress in the early growth of maize. Among the isolates, 19 bacteria that were able to grow at 4?% NaCl were used for germination assay. Two bacteria and seven bacteria significantly improved maize seed germination at 100 mM NaCl and 200 mM NaCl, respectively. Based on the presence of plant growth promoting (PGP) characters and the ability to improve seed germination, five strains were chosen for further experiments. At 0 mM NaCl, all the strains were able to increase maize shoot and root growth significantly. At 25 mM NaCl, except for Bacillus aryabhattai S210B15, all the strains were able to increase shoot and root growth significantly. At 50 mM NaCl, Bacillus aryabhattai S110B3 and B. aryabhattai S210B15 significantly improved shoot length, whereas, Pseudomonas koreensis S2CB35 and B. aryabhattai S210B15 significantly increased root length. Although salinity increased ethylene production in maize, bacterial inoculation significantly reduced the ethylene level at 0, 25 and 50 mM NaCl. Among the five strains, only P. koreensis S2CB35 showed the presence of PGP functional traits of nifH, acdS and nodA genes.