Potential of potent purple nonsulfur bacteria isolated from rice-shrimp systems to ameliorate rice (Oryza sativa L.) growth and yield in saline acid sulfate soil

In rice-shrimp farming systems, the high level of sodium that shrimps are able to grow in may create an adverse environment for rice. This research aimed to isolate purple nonsulfur bacteria (PNSB) from rice-shrimp fields and select strains that were resistant to H+, Al3+, Fe2+ and Mn2+, that can produce plant growth promoting substances such as 5-aminolevulinic acid, exopolymeric substances, indole-3-acetic acid and siderophores. The selected bacteria were applied in a soil pot experiment to determine their ability to enhance rice growth and yield. From 63 PNSB isolated from 21 paddy fields of rice-shrimp systems, four strains were selected for their properties as biofertilizers and plant growth promoters (PGP). They were all identified as strains of Luteovulum sphaeroides. A randomized complete block design incorporating six treatments was used to investigate the ability of the four PNSB strains to ameliorate rice growth and yield in saline acidic soil with saline water irrigation at 4 parts per thousand. PNSB cultures at 1.90 x 10(5) CFU g(-1 )dry soil weight were applied three times, along with normal chemical fertilizers, and all monitored parameters of rice growth and grain yield significantly improved in soil with a toxic Al3+ content of 10.8 meq 100 g(-1). A mixed four cultures most effectively increased grain yield (86.8%) compared with no applied PNSB. Remediation of the pot soil was exhibited in decreased exchangeable Na in soil and proline content in leaves. The four PNSB could act as biofertilizers, PGP and bioremediators with potential to enhance rice yield in rice-shrimp systems for sustainable rice cultivation.