Screening for complete submergence seedling tolerance in Rice (Oryza sativa L.) genotypes collected from Sudan and South Sudan

Eighteen rice genotypes from Sudan and South Sudan and two genotypes (FR13A tolerant and IR42 sensitive checks) from the International Rice Research Institute were screened for complete submergence at seedling stage in a protected house. Most of the genotypes showed zero survival, except genotypes [NBGA (2.08%), Banban (3.92%), Masury1 (5.56%), Pipanfary Red2 (11.11%) and Sommboy (14.58%)]. Sensitive genotypes registered 2 to 3 folds reduction in root length. Mean soluble sugar concentration in roots increased by 41% and decreased by 57.3 and 80.5% in stem and leaves, respectively. Mean starch concentration was reduced by 13.8% in roots and 77.7% in stems; whereas it increased by 115% in leaves for all genotypes. Genotypes with some degree of tolerance exhibited higher soluble sugar and lower starch concentrations. Submergence reduced chlorophyll a, chlorophyll b and total chlorophyll (a+b) by 83.0, 83.3 and 82.7%, respectively. Genotypes that showed survival after submergence maintained higher values of chlorophyll a, b and (a+b) as compared to other genotypes. Genotypes tolerant to submergence such as Pipanfary Red2 and Sommboy had higher soluble sugar and starch concentrations and chlorophyll content and could be developed to be grown under rain-fed lowland flooded areas of Sudan and South Sudan.