Abstract
Four experiments were conducted at the research farm of the Bangladesh Rice Research Institute (BRRI) in Comilla, Bangladesh during boro 2007-08 to boro 2009-10 with a view to select superior parental lines for heterotic hybrids in rice. Considerable variation exhibited in the parental lines for all the floral traits. Five of 11 cytoplasmic male sterile (CMS) lines viz. IR73328A, BRRI 3A, PMS 8A, Jin 23A and IR68888A and 12 of 20 restorer lines viz. Wan 3R, M. H. 77R, BR7011-37-1-2R, HP-4R, BR736R, IR73004-107-3-3-2R, Gui 99R, BR6723-1-1-2R, IR40750R, BR168R, Ajaya R and BR6839-41-5-1R were identified as superior parental lines considering desirable floral traits. Comparatively higher temperature and lower relative humidity were needed for restorer lines (31.3°C and 67.8%) than CMS lines (30.6°C and 72.8%) with the range of 30.0 -32.7°C and 58.9-76.1% for parental lines. Stigma length, angle of opening of glume, stigma exsertion and panicle exsertion of CMS lines strongly influenced outcrossing rate. Five clusters were formed and these clusters were utilized to identify superior parental lines. Significant difference in seed setting was observed in CMS lines during hand crossing with highest in PMS 8A (63.0%) and lowest in IR68888A (57.6%). The ratio of general combining ability (GCA) and specific combining ability (SCA) variances exhibited greater relevance of non-additive gene actions governing yield and its associated traits. Jin 23A and IR68888A showed significant GCA effects for short plant type and earliness; PMS 8A was best general combiner and IR73328A was average general combiner for grain yield. The restorer lines; BR6839-41-5-1R, Wan 3R, BR6723-1-1-2R, BR736R, Gui 99R, BR168R and IR73004-107-3-3-2R also showed significant GCA effects for grain yield. Thirteen hybrids viz. IR73328A/Wan 3R, IR73328A/IR73004-107-3-3-2R, IR73328A/IR40750R, IR73328A/ BR6839-41-5-1R, BRRI 3A/IR73004-107-3-3-2R, BRRI 3A/BR6839-41-5-1R, PMS 8A/ BR168R, PMS 8A/AjayaR, Jin 23A/BR6723-1-1-2R, Jin 23A/BR168R, Jin 23A/BR6839-41-5-1R, IR68888A/BR736R and IR68888A/Gui 99R were found as good specific combinations for grain yield and productivity. These 13 hybrids showed more than 15 and 10% standard heterosis over BRRI dhan28 for grain yield and productivity, respectively and might be selected for further evaluation in preliminary yield trial. The seeding interval for 50% flowering were varied from 1 - 19 days, in leaf number it varied from 0 - 4.82 and in terms of effective accumulated temperature (EAT) it varied from 13.5-282.2°C among five CMS and 12 restorer lines.