Submergence tolerance of rainfed lowland rice: search for physiological marker traits

The submergence tolerance of four rainfed lowland rice (Oryza sativa L.) cultivars was evaluated after submergence in a natural water pond for different submergence durations (0, 7, 11, and 15 days). Complete submergence of plants induced elongation and accumulation of volatile aldehydes at different rates in the cultivars studied. Total soluble carbohydrates (TSC) and starch content, on the other hand, decreased during submergence. Plant survival recorded after 10 d of desubmergence showed large cultivar differences. Plant elongation during submergence has been found to be negatively correlated with survival (r = -0.77), emphasizing the importance of reduced elongation growth during submergence. Higher amounts of starch and total soluble carbohydrate (TSC), before and at the end of submergence period, greatly improved the survival during submergence and recovery growth after desubmergence. Aldehyde content was measured in the shoots as an indicator of the shift in metabolic activity from aerobic respiration to anaerobic fermentation, which differed in tolerant and intolerant cultivars. Intolerant cultivars invariably produced more aldehydes than tolerant ones. Aldehyde production rate was negatively correlated with plant survival, suggesting that plants utilizing excess energy reserve during submergence stress suffered the most, resulting in poor survival. Our results suggest that greater elongation growth during submergence has pronounced adverse effects on rice plant survival during submergence, and that higher initial carbohydrate (soluble sugar and starch) enable rice plants to sustain submergence stress and regenerate quickly after desubmergence. These findings are discussed in relation to adaptation traits for submergence tolerance in rainfed lowland rice.