Elongation ability and non-structural carbohydrate levels in relation to submergence tolerance in rice

Flash flooding adversely affects rice productivity in vast areas of rainfed lowlands in South and Southeast Asia. Tolerant genotypes were identified and key traits such as high levels of non-structural carbohydrates (NSC, starch and soluble sugars) and limited underwater elongation were found to be associated with tolerance. In this study, we evaluated the role of NSC before and after submergence and shoot elongation during submergence in submergence tolerance using genotypes that contrast in initial NSC content and elongation ability during submergence. The traits were further manipulated using a growth promoter, GA(3), and a potent gibberellin synthesis inhibitor, paclobutrazol (PB). Submergence for 10 days resulted in higher mortality of IR42 (intolerant), followed by Sabita and Hatipanjari. The latter two cultivars have a high initial NSC similar to that of the tolerant cultivar, FR13A, but elongated to higher extent under water. Exogenous GA(3) enhanced underwater elongation and depletion of NSC and reduced survival. Conversely, PB suppressed elongation, improved the retention of NSC and enhanced survival. FR13A is less responsive to PB but more responsive to GA, suggesting its inherently low GA concentration under submergence. Underwater elongation is associated with NSC consumed during submergence but not with NSC level before submergence. Seedling survival showed a stronger association with NSC maintained after submergence (r(2) = 0.74) than with NSC before submergence (r(2) = 0.27). This suggests that carbohydrates maintained after submergence, being the result of both initial level, and the level used during submergence, is more important for survival. (C) 2004 Elsevier Ireland Ltd. All rights reserved.