Exploring the Saline Pokkali Rice Field for a Multi-Traited Biostimulant to Alleviate Salt Stress in Rice

Climatic change due to global warming has augmented salinity intrusion and soil salinization, harming crop yields.The identification and utilization of salt tolerant native microbiota with potential plant growth promoting traits seems to be an effective alternative for salt adapted smart agriculture. The innovative aspect of this study is the exploration of potential microbes associated with native salt tolerant crop varieties for salinity management, which could offer a sustainable and cost-effective solution. The present study was conducted in saline Pokkali rice field from Alappuzha district, Kerala, South India which holds a high geographical significance. Soil samples were collected in monthly interval for a period of one year from January 2019 to January 2020 for isolation and characterization of potential salt tolerant plant growth-promoting rhizobacteria (ST-PGPRs) and soil analysis. Soil samples from Pokkali rice fields exhibited dynamic variations in salinity and pH, ranging annually from 1.1dSm^− 1 to 8.5 dSm^− 1 and pH 4 to 5.9. We isolated a total of 50 rhizobacterial strains, which were screened for the biochemical and salt tolerant traits and identified PK7 as a potential ST-PGPR strain. Molecular identification with 16 S rRNA gene sequencing and phylogenetic analysis showed that the closest reference to PK7 is Pseudomonas taiwanensis and was submitted to GenBank with accession No. MT218377. The efficacy of selected strain on rice was analysed in-vitro controlled conditions using salt sensitive and salt tolerant varieties under salt stress. Morphological parameters and vigour index were compared and increased germination percentage as well as vigour index with statistical significance (**P < .01) were observed. Further investigations conducted on chlorophyll and proline content in rice seedlings after induced salt stress revealed that the isolated ST-PGPR strain PK7 had increased the chlorophyll and proline content, indicating salt stress resistance. The isolated strain PK7 from saline Pokkali rice fields was found to be a promising microbe as an effective bioinoculant for sustainable crop improvement under salinity.