ESTIMATION COMBINING ABILITY AND HETEROSIS FOR GRAIN YIELD AND ITS RELATED TRAITS IN RICE UNDER WATER STRESS CONDITION

Combining ability analysis was carried out in rice through A 8 x 8 diallel set analysis excluding reciprocals involving 8 diverse parents for grain yield and some yield related traits at the Experimental Farm of Rice Research and Training Center, Sakha, Kafr El-Sheikh, Egypt during 2007 and 2008 summer seasons. The ratio of variances due to general and specific combining abilities (ó GCA / ó SCA) was more than unity, indicating the preponderance of additive genes in controlling for 100-grain weight (g). On the contrary, predominance of non-additive gene action chiefly controlled the expression of days to 50% heading, plant height, panicle length, number of panicles/plant, sterility (%) and grain yield/plant. Among the parents, IET 1444, Wab 450 and Balado were found to be significantly superior general combiners for grain yield/plant. The genotypes IET 1444 and Wab 878 were good general combiners for plant height, panicle length and sterility (%). Moreover, Balado, Wab 450 and Wab 878 were the best general combiners for 100-grain weight. On the other hand, Sakha 102, Balado and Gaori rice varieties were good combiners for earliness. In addition, a total of 14 crosses exhibited positive and highly significant SCA for grain yield /plant. The promising combinations for grain yield and most of the studied traits were Sakha 102 X Sakha 104, Wab 450 X IET 1444, Wab 450 X GZ 1368 and IET 1444 X Wab 878. It is observed that majority of the crosses with high SCA for grain yield were resulted from low / low or high / high or high / low combining parents. Highly significant negative estimates of SCA for number of days to 50% heading (earliness) were recorded for Wab 450 X Wab 878, Sakha 102 X Sakha 104 and Wab 450 X GZ 1368 cross combinations. Moreover, 16 cross combinations were found to be the best specific combinations for plant height. The cross combinations, Sakha 102 X IET 1444, Sakha 104 X IET 1444, Sakha 104 X Wab 878 and Wab 450 X GZ 1368 were the best specific combinations for panicle length and number of panicles /plant. Ten cross combinations exhibited highly significant and negative SCA effects for sterility %, while, nineteen crosses were the best cross combinations for 100-grain weight. The results also revealed that, a greater magnitude of heterosis when it measured as a deviation from mid-parent and better parent was observed in Wab 450 X Wab 878, Wab 878 X Gaori, Sakha 104 X Wab 878, IET 1444 X Wab 878, Wab 450 X Gaori and Sakha 102 X GZ 1368 rice crosses for grain yield /plant. Grain yield was positively and strongly correlated with each of number of panicles/plant (0.563), 100 grain weight (0.659) and panicle length (0.330). However, a highly significant and positive estimate of phenotypic correlation coefficient (0.574) was recorded between plant height and panicle length. On the other hand, significant negative estimates of phenotypic correlation coefficients were recorded between number of panicles/plant and each of panicle length (-0.445) and 100-grain weight (-0.295), and between the last ones and panicle length (-0.312).