Phenotypic Screening of Nigerian Rainfed Lowland Mega Rice Varieties for Submergence Tolerance

摘要

The submergence tolerance of 20 rainfed lowland rice (Oryza sativa L.) cultivars consisting of six Nigerian rainfed lowland mega rice cultivars, five Asian submergence tolerant mega varieties, four landraces, two lowland NERICAs and three parents of Subl varieties were evaluated in a natural water pond that allows maintenance of flood water depth of 1.5 m for a period of 14 days. The experiment was laid out in a randomized complete block design with three replicates. Seeds sown in the wet nursery were transplanted after 21 days to the puddle soil in the deep pond at 20 cm × 20 cm with two seedlings per hill in eight rows of 5 m~2. Ten extra rows of susceptible varieties (IR42) were planted on one side of the pond to observe the extent of damage due to submergence. Thirty-day old seedlings were submerged for 14 days under 100 cm of water followed by normal condition. Survival counts were taken visually 10 days after withdrawal of flood water. Data were also collected on plants for stem elongation, date at 50% flowering, plant height, number of tillers at maturity, number of panicles at maturity and grain weight. Plant survival recorded 10 days after de-submergence showed large cultivar differences. Percentage survival varied from 3.2 to 97.5%. All mega varieties with Subl gene had a significantly higher percentage survival and grain yield. Comparing the grain yields as influenced by submergence with grain yields obtained under normal lowland rainfed condition, FARO 57, a susceptible variety, was found to have the highest percentage yield reduction of 98.5%. Plant elongation during submergence was found to be negatively correlated with survival (r = -0.80), indicating the importance of reduced elongation growth during submergence.