GENETIC STUDIES OF LOWLAND RICE (Oryza sativa L.) FOR SUBMERGENCE TOLERANCE IN NIGERI

Abstract

Submergence tolerance has long been regarded as an important breeding objective for rain-fed lowland and deep-water rice areas. Despite this recognition, there has been limited success in developing improved submergence tolerant rice varieties in Africa particularly Nigeria. In this research, study on genetics of Oryza sativa lowland rice for submergence tolerance was carried out, using two most farmer-preferred commercial rice varieties in Nigeria. Six generations were developed by crossing a submergence tolerant donor rice line (Swarna Sub-1) with the two commercial varieties (FARO 44 and FARO 57). The six generations of the two crosses were evaluated under submergence stressed and non-stressed conditions. The inheritance of the tolerant gene (SUB-1 gene) was determined by Mendelian Ratio and the nature of gene actions for some important agronomic traits of the generations was estimated by generation mean analysis. The submergence screening was performed in a controlled condition that allowed flooding with water depth of 1.0 metres for a period of 14 days. The evaluation was done in a complete randomized block design with three replications. Data were collected on Percentage Survival of the test entries, Percentage Survival of the resistant entries, Percentage Comparative Survival, Percentage Elongation, Plant height (cm), Number of tillers per plant, Days to 50% flowering, 100 grain weight (g), Panicle length (cm), Panicle number, Grain width (mm), Grain length (mm), Flag leaf width (cm), Flag leaf length (cm), Straw girth (mm), and Internode length. The result revealed that the Analysis of Variance were significantly different for all the traits at both vegetative and reproductive growths, except for the flag leaf width (FLW) and Stem Girth (SG) in both crosses under normal condition. Survival rate (%) ranged between 0.00% - 100% was observed in the Cross I. In the Cross II, a range between 0.00% and 95.24% survival rate was recorded. High Phenotypic Coefficient of Variation (PCV) and Genotypic Coefficient of Variation (GCV) were registered for the grain yield among the generations of the two crosses. Moderate to high narrow sense heritability in conjunction with moderate to high expected gain were observed in most of the traits, especially the yield component traits. The results of the generation mean analysis showed significance of at least one out of the four scales (A, B, C and D) for all the traits studied in the two crosses. The six parameters analyzed revealed that besides the additive and dominance gene actions, epistatic interaction mechanisms have also contributed to the expressions of the traits studied. However, the relative magnitudes of these effects varied from character to character and cross to cross. Despite the stressed conditions of submergence, the introgression of the Sub1A gene demonstrated considerable improved survival ratio and 54.1% to 66% obtainable grain yield after recovery from complete submergence of the rice field. This can be the next quick crop development area to be considered which would help generate desirable varieties for the Nigerian farmers especially with the consistent flood being experienced in our unpredictable weather faced with climate change