Rice seed endophytes transmit into the plant seedling, promote plant growth and inhibit fungal phytopathogens

Research on seed microbiota gained much attention as it constitutes a primary inoculum for plants and supports their growth, fitness and productivity. This research aimed to explore the uniqueness and impact of culturable seed-endophytes on a widely cultivated rice host plant. In this report, we present the nature of seed-borne endophytic bacteria from cultivated rice ( Oryza sativa L.) variety Ajinkya-1040 and their crucial roles in plant growth promotion and biocontrol. We report characters of five culturable rice-seed-borne endophytic bacteria Bacillus sp. RSE01, Citrobacter sp. RSE02, Citrobacter sp. RSE03, Flavobacterium sp. RSE04, and Pantoea sp. RSE05 which are not reported before from seeds of rice cultivars. These isolates showed plant growth-promoting activities by producing phytohormones, siderophores, ammonia, hydrogen cyanide (HCN), solubilizing minerals or by fixing N 2 and showed antagonistic effects against various fungal pathogens of rice. Among the isolates, Citrobacter sp. RSE02 showed highest IAA (34.51 ± 0.23 µg/mL), GA (55.43 ± 0.29 µg/mL), siderophore (95.68%) and HCN production ability. Whereas, Pantoea sp. RSE05 showed the highest efficacy for phosphate (83.19 ± 1.45), potassium solubilization (82.27 ± 0.6 µg/mL) as well as ammonia-producing efficiency. Furthermore, these seed endophytes can readily migrate from the seeds to the roots and shoots of the germinated seedlings. Seedlings fortified with the endophytic culture showed an overall increase in root and shoot length (1.5-fold and 2-fold, respectively). Most of the isolates inhibit the mycelial growth of selected fungal pathogens of rice. These results suggest that the isolated seed endophytes can potentially be used to assist plant growth and development and help host plant to fight against fungal phytopathogens for eco-friendly and sustainable agriculture. Graphical Abstract