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

Background and aim Rhizosphere function is the key determinant of crop growth and fitness under moisture-stress conditions. Human-centered breeding adversely affects microbiome recruitment of crops. Hence, during drought, wild types and landraces adapt to stress, while modern cultivars and hybrids fail to do so and are susceptible to drought. Understanding the rhizosphere difference between landraces and cultivars will help to improve microbiome-mediated drought mitigation. Methods We compared rhizospheres of rice landrace, Norungan, and high-yielding cultivar, Co51, grown under normal moisture and drought-induced conditions using soil biochemical and 16S rRNA gene sequencing approach. Results Soil carbon pools, enzymes, and respiration were adversely affected due to drought in both genotypes' rhizospheres. However, Norungan rhizosphere accounted for less harm to the soil attributes than Co51. Reduction in soil organic carbon (3.94%), microbial biomass carbon (14.26%), labile carbon (1.94%), dehydrogenase (10.1%), urease (21.27%), phosphatase (9.61%), and respiration rate (15.02%) was accounted in Co51 than Norungan, during drought. Alpha diversity of bacterial communities in rice's rhizosphere was significantly lower than in bulk soil, and drought further reduced the diversity in both genotypes. Moisture-stress reduced the abundance of Firmicutes (180%) and Bacteroidetes (57%) in Norungan's rhizosphere, while, Acidobacteria (51%), Actinobacteria (54%), Chlolorflexi (41%), and Proteobacteria (34%) got increased. On the other hand, Co51 rhizosphere acquired an enhanced abundance of Firmicutes (79%) and Bacteriodetes (170%) and lessened abundance of Acidobacteria (15%) and Proteobacteria (31%) due to drought. Conclusion These results suggest that landrace Norungan under moisture-stress conditions recruits less-diversified, specific groups of microorganisms to augment rhizosphere functioning.