Breeding rice for abiotic stress tolerance is very important objective for rice breeders. Significantly reduce in yield due to drought-stress in most world countries, especially suffering from water lace as well as Egypt. Evaluating combining ability effects would provide valuable information that can be used for developing new drought tolerant lines. This study was conducted at Sakha Agricultural Research Station during 2014 to 2016 rice growing seasons to determine combining ability and gene action for grain yield and other important traits to identify the superior varieties/parents and crosses under both drought and optimum conditions. Six F 1 hybrids were generated by crossing four rice genotypes in a half diallel mating scheme in addition to their six F 2 populations after self-pollination. The four populations (P 1 , P 2 , F 1 and F 2 ) for all the six crosses were evaluated in a replicated field trial under drought and normal conditions. Drought stress significantly decreased the mean values of all the studied traits for parents and their hybrids compared with the control condition. Significant differences were observed among parents and their hybrids for most traits under both research conditions. General combining ability (GCA) and specific combining ability (SCA) means squares were highly significant for grain yield and most traits under test environments. The non-additive gene action played an important role in the inheritance of most studied traits. The parental genotypes NERICA3 and NERICA4 appeared to be the best general combiners for earliness and grain yield. The cross combinations; Giza178×NERICA3; Giza178×NERICA4 and NERICA3×NERICA4 in both F 1 and their F 2 generations were distinguished as specific combiners for grain yield and other related traits under normal and drought conditions. These results emphasized by positive heterosis over high parents followed by high values of inbreeding depression. Hence, these hybrids would be valuable in rice breeding for improving grain yield under drought stress condition.
B REEDING rice for cold tolerance is one of the important ways for climate change facing, which attacks a large amount of the cultivated areas all over the world countries. This study was perfomed at Sakha Agricultural Research Station during two rice growing seasons 2015 and 2016 to evaluate some rice accessions which belong to different rice types for the ability of cold tolerance in seedling stage at early growing season under Egyptian conditions. The 40 rice accessions used in this study were evaluated at two early dates of sowing 1 st March and 1 st April as a cold condition, in addition to control sowing date at 1 st May. Twenty six SSR markers related to cold tolerance at seedling stage were used in order to determine the genetic diversity and polymorphism among the studied genotypes. Low temperature degree condition significantly decreased the mean values of the all studied traits for all accessions compared with the control condition. Significant differences were observed among the studied genotypes under both different growing conditions. Japonica varieties are found to be more tolerant than Indica varieties. SSR markers RM265, RM324, RM163 and RM270 showed highly polymorphism among the studied rice accessions and more over differentiate them to different groups based on their ability for cold tolerance. Giza 177, Sakha 102 and Sakha 104 out of the Egyptian rice genotypes showed a good performance at low temperature degrees condition in early growing season. The genotypes CT6749-36-7-2-M-M, Milyang 80, PSRM1-17-4B-13, Ryong Sung 25 can be used as a donor for cold tolerance in rice breeding program.
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