Submergence tolerance and tolerance mechanism: A study on traditional and improved rice genotypes at the seedling stage under complete submergence stress in Sri Lanka

Abstract

Submergence-tolerant genotypes in rice are essential for flood-prone lands, and recent studies have focused on dissecting tolerance mechanisms considering morphological and physiological changes in the plants upon submergence. Thirty improved rice varieties and sixty-two traditional rice accessions were screened for submergence tolerance under complete 9-day and 14-day submergence stress at the two-week-old seedling stage. The submergence tolerance level of each rice genotype was evaluated according to IRRI guidelines based on survival rates. Accordingly, rice genotypes were categorized into four groups: tolerant, moderately tolerant, moderately susceptible, and highly susceptible. Two Mawee accessions (3704, 3618) were submergence tolerant at 14-day submergence stress. The traditional rice accessions Ratawee3466, Mawee (8552, 4145), and Heenati4935 and improved rice varieties Bw400 were moderately submergence tolerant at 14-day submergence stress. Survival rates of the rice genotypes, their initial plant height, and shoot elongation at 9-day and 14-day submergence stress showed that seedling elongation (escape strategy) or reduction of elongation compared to control plants (quiescence strategy) under submergence stress cannot be used as phenotypic markers for selecting rice genotypes for submergence tolerance in rice. Further, the escape strategy or the quiescence strategy was not unique to the genotype, and the survival strategy of some rice genotypes changed with prolonged submergence stress. The escape strategy tended to be an SOS (Save Our Souls) strategy under prolonged submergence stress from 9 days to 14 days. No correlations between initial plant height and survival rate or survival rate and the height gain or reduction at 9-day and 14-day submergence stress showed that the submergence tolerance mechanism in rice was genotype-specific. The submergence-tolerant and moderately tolerant rice genotypes could be further investigated in future studies.