Abstract

                                The landraces and wild species wisely choose their microbiome and explored them as a second genome for nutrient acquisition from the limited resources of the soil ecosystem and can withstand drought and diseases. Hence, the present study aimed to explore the drought-tolerant rice landrace of Tamil Nadu for the putative competitive endophytes to develop a plant-growth-promoting endophytic bacterial inoculant. Twenty two putative competitive endophytes were authenticated from plant tissues and seeds of Norungan. The 16S rRNA gene sequencing revealed that Norungan rice was colonized predominantly by Firmicutes, including six species of Bacillus, four species of Priestia, and one species each of Micrococcus, Geobacillus, and Lysinibacillus, along with two Proteobacteria, Enterobacter cloacae and Kosakonia oryzae. These endophytes were screened for nutrient transformation, growth hormone production, drought mitigation, and antagonism against plant pathogens. Bacillus cereus NE07, B. paralicheniformis NE18, B. subtilis NE20, and Priestia flexa NE09 showed potential nutrient-transforming capability, while Bacillus cereus NE07 and Priestia flexa NE09 showed high plant growth hormones (indole-3-acetic acid and gibberellic acid production). Similarly, Bacillus cereus NE07 and Priestia endophytica (NE14) showed high ACC deaminase, proline accumulation, biofilm production, and potential candidates for drought mitigation. Bacillus hayneshii NE04 and Priestia aryabhattai NE10, and Bacillus cereus NE07 showed antagonism against fungal pathogen Rhizoctonia solani and bacterial leaf blight causing Xanthomonas oryzae. The results confirmed that no single strain with all plant-growth-promoting and stress-mitigating traits found in Norungan, and these strains were performed division of labor basis. Hence, developing a putative competitive endophytic bacterial consortium with compatible strains representing cumulative beneficial traits as inoculants would be a novel approach for improving rice productivity.

Key words : Drought mitigation; Norungan; PGPR; Putative competitive endophytes; Rice landrace