Endophytic fungus Stagonosporopsis ajaci NEAU-BLH1 from Adonis amurensis enhances seed germination under low-temperature stress and increases grain yield in direct-seeded rice.

Rice direct-seeding technology is regarded as a promising alternative to traditional transplanting due to its labor- and water-saving benefits. However, poor seedling emergence and growth under low-temperature stress remain major obstacles to its widespread adoption in Heilongjiang Province, China. Here, we isolated an endophytic fungus Stagonosporopsis ajaci NEAU-BLH1 from the cold-resistant plant Adonis amurensis, which effectively enhanced rice seed germination and seedling growth under low-temperature stress. Two years of pot and field experiments demonstrated that soaking rice seeds in a spore suspension of NEAU-BLH1 significantly increased tillering, resulting in a 16.0-47.8 % improvement in yield for direct-seeded rice. Mechanistic investigations revealed that NEAU-BLH1 treatment elevated gibberellin levels and reduced abscisic acid, accelerating starch hydrolysis into soluble sugars, thus improving germination under low temperature. Comprehensive physiological, transcriptomic, and metabolomic analyses indicated that NEAU-BLH1 enhances seedling growth by boosting respiratory metabolism, mitigating oxidative damage, and modulating hormone pathways. These findings indicate that seed-soaking with NEAU-BLH1 has good potential to enhance seed germination under low-temperature stress and increases grain yield in direct-seeded rice.