COMBINING ABILITY FOR GRAIN YIELD AND SOME DISEASES RESISTANCE TRAITS IN RICE (Oryza sativa L.) UNDER SALINE SOILS CONDITIONS

Combining ability analysis was carried out in rice through A 6 x 6 diallel set analysis excluding reciprocals involving 6 diverse parents for grain yield and some diseases resistance traits, at Rice Salinity Program at Serw farm, during 2007 and 2008 summer seasons. The ratio of variances due to general combining ability and specific combining ability (ó2 GCA / ó2 SCA) was more than unity, indicating the preponderance of additive genes in controlling, chlorophyll content, plant height, days to 50% heading, number of panicles/plant, both percentage and severity of brown spot, and grain yield/plant. Moreover, additive x additive type of gene interaction was played an important role in the inheritance of praline content and osmotic pressure. On the contrary, Predominance of non-additive gene action chiefly controlled the expression of panicle length; number of filled grains/panicle and 1000-grain weight traits. Among the parents, Sakha 101 was found to be significantly superior general combiner for all the studied traits except, earliness, chlorophyll content and both percentage and severity of brown spot. The genotypes Sakha 102 and Sakha 103 were good general combiners for earliness, chlorophyll content, and both percentage and severity of brown spot, and Sakha 104 for panicle length, 1000-grain weight, grain yield /plant , proline content, osmotic pressure and both percentage and severity of brown spot, Giza 177 and Giza 178 for earliness. Cross combinations, Giza 177 x Sakha 103, Giza 178 x Sakha 102 and Sakha 103 x Sakha 104 gave high SCA effects for number of filled grains/panicle and grain yield/plant. Seven hybrids for both percentage and severity of brown spot and 3 hybrids for plant height and days to 50% heading expressed desired significant negative SCA effects. In addition, Giza 177 x Sakha101 and Giza 178 x Sakha101 were found to be the superior cross combinations for panicle length, 1000-grain weight and chlorophyll content; and Sakha 101 X Sakha 104 for proline content and osmotic pressure. The values of mean degree of dominance (H1/D) exhibited over dominance with a value above the unity for all agronomic, yield and its component traits; and chlorophyll content while the other remaining traits were controlled by partial dominance. The ratio of dominant and recessive genes (KD/KR) in the parents was high than unity for all the studied traits except plant height, days to 50% heading, panicle length and proline content indicating more of dominant genes in the parental lines than recessive genes. High estimates of broad sense heritability was recorded for all the traits, it was ranged between 94.4% and 98.7% for osmotic pressure and percentage of brown spot disease. In addition, high estimates of heritability in narrow sense were recorded for proline content, osmotic pressure and both percentage and severity brown spot disease.Results of field tests revealed that 12 entries were resistant to blast,four moderately resistant,four susceptible,and only one highly susceptible,three inbred varieties were completely free from false smut,inaddition to five hybrids For white tip nematode,ten hybrids were not infected,but three inbred varieties had considerable infection.for brown spot the highest infected varieties were sakha 101 and Giza 177,while the lowest were Sakha 103 and Sakha104.However,the hybrids had generally lower infection than inbreeds. Results of greenhouse test showed that nine entries performed resistance to both races, while six entries were moderately resistant Shehata, S. M. et al. 7216 to RaceIG1,and four entries were moderately resistant to Race IB45.On the other hand, three and four entries were susceptible to the first and second races respectively.