Internode elongation pattern and differential response of rice genotypes to varying levels of flood water.

Rice plants are damaged during floods by complete or partial submergence. The pattern of expression of rice plant varies with different flood regimes. Accordingly, the morphological and physiological responses of rice genotypes were studied in field and pot experiments under different flood regimes. Wide genetic base lines of Oryza sativa and sub 1 introgressed submergence tolerant were compared in field experiments using principle component analysis. Further, based on internode elongation pattern, two genotypes - Bodikaburi and Pokkali - were selected for a pot experiment to find more on elongation pattern of internodes under different flood regimes. Short-term submergence in minimal water, elongation of blade, sheath, leaf area, DW, number of nodes in primary stem and survival present showed strong positive relationship with shoot length. Number of tillers, leaf area and DW were more affected and decreased during submergence than its non-submergence counterpart. Under different flooding regimes, cvv Bodikaburi and Pokkali exhibited different behaviour in the elongation pattern of the shoot. Partial submergence accelerated elongation of all internodes whereas complete submergence accelerated the top internode. Enhancement of shoot elongation during submergence in water is an escape strategy adopted by rice to resume aerobic metabolism and to improve carbon fixation. This escape strategy varies among genotypes with respect to different flooding regimes. Therefore, breeders should be aware of breeding of rice plants with suitable architecture for different flood- prone environments.