Phenotypic evaluation of local rice (Oryza sativa L.) landraces for tolerance to submergence stress

Rice seedlings are often subjected to abiotic stresses, particularly flooding and submergence in lowland areas, highlighting the need to develop genotypes with improved tolerance to these conditions. This study aimed to evaluate the submergence tolerance of seven rice genotypes and identify adaptive traits associated with survival under complete submergence. Seven genotypes were phenotypically evaluated under complete submergence (155 cm water depth, 10 days) in a Completely Randomized Design (CRD) with nine replications. After a seven-day recovery period, the landraces were evaluated for survival, shoot elongation, biomass accumulation, green leaf retention, and chlorophyll content. All variables across stages showed significant genotypic variation (P ≤ 0.001), suggesting that the landraces used different adaptive methods. Sawa Mansuli Sub-1 and Chamse 6-mahine showed minimal elongation, superior leaf retention, higher chlorophyll content, and significantly greater survival; excessive shoot elongation, especially in Chamse 3-mahine, was linked to high biomass accumulation during submergence but highest mortality after recovery. Principal component analysis distinguished quiescence-type landraces (Sawa Mansuli Sub-1, Chamse 6-mahine, and Seto Bikashi) from susceptible escape-type landraces, with PC1 and PC2 explaining 95.8% of total variation. Correlation analysis revealed a negative association between shoot elongation and survival and positive associations between survival and post-recovery biomass, green leaf retention, and chlorophyll content. Although field testing and genetic research are still required, these results indicate that Chamse 6-mahine and Seto Bikashi are promising local rice varieties for creating flood-tolerant rice. Furthermore, they highlight quiescence-based energy conservation, chlorophyll content, and leaf viability as important determinants of submergence tolerance.