Potential of biofertilizers from selected Rhodopseudomonas palustris strains to assist rice (Oryza sativa L. subsp indica) growth under salt stress and to reduce greenhouse gas emissions

The absence of phytotoxicity is one of the most important criterions for the use of biofertilizers, and their carriers must be able to maintain their activity efficiently until used. Hence, a carrier that consisted of a mixture of rice straw and rice husk ash in a 4: 1 ratio with potential biofertilizers (Rhodopseudomonas palustris TK103, PP803, and P1) were investigated with a salt sensitive rice for seed germination assay and the efficacy of the biofertilizers to ameliorate rice growth under salt stress (0.25 % NaCl) by producing 5-aminolevulinic acid (ALA) and reducing gas emissions (CH4 and CO2). No phytotoxicity was found under optimal concentrations for any of the biofertilizers tested as the germination index (GI) in the range of 105-0117 %; however, the carrier had a 94 % GI when compared with distilled water. Among the biofertilizers tested, strain PP803 was the best to ameliorate rice seedling growth in soil under salt stress, particularly on plant height and root length when compared with carrier and water controls. In a paddy field model study under microaerobic light conditions for 10 days, optimal concentrations of biofertilizers provided viable cells in the range of 6.7-6.8 log CFU mL(-1), and strain PP803 was the most effective fertilizer to produce maximum ALA (2.61 mu M) and reduce 100 % CH4 and 47% CO2 emissions. It can be concluded that the biofertilizers tested, particularly the strain PP803, could be powerful agents for use in saline paddy fields to ameliorate rice seedlings growth under salt stress and reduce greenhouse gas emissions.