Early seedling vigor for direct-seeded rice: traits, mechanisms, and improvement strategies- a review

Direct-seeded rice (DSR) is emerging as a sustainable alternative to traditional transplanted systems because of its lower water and labor requirements. However, successful crop establishment under DSR is heavily dependent on early seedling vigor (ESV), a multidimensional trait involving rapid germination, uniform emergence, mesocotyl elongation, and biomass accumulation during the initial growth stage. ESV plays a key role in providing a competitive advantage against weeds and supporting resilience under environmental stress. Despite its agronomic significance, ESV has not been a primary selection trait in conventional rice breeding because of its quantitative nature and complex inheritance. Recent advances in high-throughput phenotyping, physiological trait analysis, functional genomics, QTL mapping, GWAS, and haplotype-based breeding have significantly improved our understanding of the genetic and molecular basis of ESV. Key hormonal regulators, such as gibberellins, abscisic acid, brassinosteroids, and cytokinins, along with biochemical components, such as amylase activity, antioxidant enzymes, and carbohydrate metabolism, contribute substantially to seedling vigor. Marker-assisted selection and the integration of multi-omics data are now enabling the precise introgression of ESV-associated QTLs into elite backgrounds. This review consolidates the current research progress on the physiological, morphological, and biochemical traits of ESV in rice and highlights breeding strategies that harness genetic variability and advanced genomic tools to develop rice cultivars that are well-suited for direct-seeded conditions.