Abstract
Forty seven parental lines comprising seven CMS with different cyto-sources, ten maintainers and thirty restorer lines were studied in respect to floral biology, yield contributing traits, genetic divergence among them to select best performing CMS maintainer and restorer lines for developing heterotic hybrid rice. Fertility restoration systems of different CMS lines with restorer lines were also assessed. The research was carried out during the period from July 2007 to May 2009 in the research field of Bangladesh Rice Research Institute, Gazipur. Floral traits related to cross-fertilization were studied in CMS, maintainer and restorer lines. Among the traits, duration to open florets, angle of open florets, panicle exertion rate, stigma exertion rate, outcrossing rate and days to panicle emergence played very important role for seed setting in CMS lines. Similar traits were very important for maintainer lines except outcrossing rate. BRRI9A was found most suitable for angle of open florets, stigma length, stigma breadth, anther breadth, filament length, style length, percent panicle exertion and stigma exertion rate while corresponding maintainer line BRRI9B was found suitable for duration to open florets, stigma length, stigma breadth, anther breadth and filament length. Outcross influencing floral traits like duration of bloom florets, filament length and no. of pollen/focus varied significantly among the restorer lines. Based on yield contributing characters BRRI9B and BR168R were found most promising. In diversity analysis maintainer and restorer lines were grouped into four different clusters based on their maturity. Clusters showing maximum divergence among them were also genetically distant from each other for the relevant traits. Most divergent type was observed in cluster 2 in maintainer lines and showed maximum distances from cluster centroids. Similarly in respect of restorer lines cluster 2 contained maximum number of genotypes and showed maximum diversity regarding maturity. Restorer lines grouped into cluster 1 showed maximum distances from cluster centroids. Inheritance of fertility restoration was studied in crosses involving ten elite restorer lines with CMS line II32A (ID) and BRRI9A (Gam). The segregating pattern of pollen fertility of F2 and BC1 population of crosses involving П32A and BRRI9A indicated the presence of two independent dominant fertility restoring genes. The mode of action of the two genes varied in different crosses indicating three types of interaction and that was epistasis with dominant gene action, epistasis with recessive gene action and semi-epistasis. Semi-epistasis might be happened due to presence of modifier genes. Selection of parents as well as crosses was made based on the results of Line x Tester analysis. Seven CMS lines and ten restorers were used in this regard. The over all findings showed both additive and non-additive gene action were predominant in the studied traits, but most of the traits were under control of non-additive gene action. The prevalence of non-additive gene action implies that all the characters could be improved through heterosis breeding. The CMS line BRRI9A was selected as good general combiner for panicle length, panicle weight, spikelet fertility (%), 1000 grain weight and grain yield/plant. Restorer line BR168R and BR6723-1-1-2R were considered as the best general combiner for earliness, effective tillers/plant, panicle length, panicle weight, spikelet fertility (%) and grain yield/plant. The hybrids BRRI9A/BR168R, IR78362A/IR44675R and IR58025A/M.H.77R exhibited highly significant negative sca effects for plant height indicating good specific combiner for dwarfness. Maximum specific combining ability for grain yield/plot was observed in IR78362A/IR64R. The hybrid combination BRRI9A/BR168R showed highest standard heterosis over BRRIdhan28 (67.13%) and BRRIdhan29 (33.97%). Considering the character association maximum numbers of heterotic crosses were found from medium x low GCA parental combinations. The results indicated that additive x additive and additive x dominance type of gene interaction was responsible for the manifestation of high heterosis.