PLANT CELL BIOTECHNOLOGY AND MOLECULAR BIOLOGY

Salinity limits rice establishment and productivity, particularly during early growth. This study investigated pairwise epistatic quantitative trait loci (QTLs) associated with seven morpho-physiological responses to salt stress at the seedling stage in rice. A mapping population comprising 234 F₂ individuals derived from MTU 1061 (salt-tolerant) × MTU 1121 (salt-susceptible) was genotyped using 104 polymorphic simple sequence repeat (SSR) markers. Their F₂:₃ progenies and the parental cultivars were evaluated in a hydroponic screening system with salinity increased from an electrical conductivity of 6 to 12 dS m⁻¹. Salt injury score, shoot sodium and potassium concentrations, shoot Na⁺/K⁺ ratio, shoot length, root length and shoot dry weight were recorded. A linkage map covering 12 rice chromosomes spanned 2,956.12 cM. Interval mapping for epistatic interactions (IM-EPI) identified 257 QTL pairs across these seven traits: 32 for salt injury score, 21 for shoot Na⁺ concentration, 15 for shoot K⁺ concentration, 52 for the shoot Na⁺/K⁺ ratio, 60 for shoot length, 72 for root length and 5 for shoot dry weight. The distribution of interactions across traits suggests that pairwise genetic effects contribute to variation in seedling responses to salinity. The mapped regions provide a basis for further examination of the genetic architecture of seedling-stage salt tolerance, although their utility for marker-assisted selection requires validation.