Inheritance of tolerance to seedling submergence in rice genotypes in Uganda
Mlaki, Anna B
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Normal growth of rice seedlings is affected when subjected to a prolonged period of submergence. The effects of submergence vary among different rice genotypes. This problem is more pronounced when fields are not well leveled and are irrigated by surface flooding. Majority of lowland rice fields in East African are of this nature and are thus prone to submergence and corresponding yield losses. In Uganda, 59% of rice is grown under rain-fed lowland ecologies. These environments receive above normal rains which can reach flood level. Yield losses ranging from 10% to 100% have been reported as result of submergence worldwide. To address this problem, breeding for submergence tolerance is the most ideal and promising strategy in rice. At the moment, there are no submergence-tolerant rice varieties identified in Uganda. This study aimed to understand the morphological, physiological and genetic basis of tolerance to submergence and to identify submergence tolerant rice genotypes among selected rice genotypes in Uganda. Twenty nine (29) and thirty four (34) rice genotypes were screened for submergence tolerance at seedling stage using morphological and molecular methods respectively. Morphological characterization was conducted in the screen house and under field conditions. Results suggested significant differences in the performance of genotypes both in the screen house and under field conditions. Genotypes Swarna, IRRI SUPA 3 and KOMBOKA showed ≥ 80% survival rate with Swarna genotype ranking first. Molecular characterization of tolerance to submergence revealed that out of 34 genotypes, 30 scored presence for Sub1A-2 allele while four genotypes were neither Sub1A-1 nor Sub1A-2 which suggested the escape strategy as a mechanisms used by genotypes to survive submergence stress. Molecular marker RM 444 was found to be polymorphic and could be used in breeding programme for marker assisted selection. Evaluation of inheritance for submergence tolerance showed that general combining ability (GCA) effects were significant unlike specific combining ability (SCA) effects. This suggested that tolerance to submergence was mainly controlled by additive gene effects among the twenty four F2 families studied. The estimated narrow sense coefficient of genetic determination was moderately high (0.73) for seedling survival, suggesting that early-generation selection would probably be effective. The resistant parents Swarna and KOMBOKA had very-good aptitude of transmission for tolerance to submergence and can be used to improve locally well adapted rice genotypes in Uganda.