Gene action and combining ability for grain yield and its components in rice

In this study, an effort was made to identify good parents and nature of gene action governing different characters of rice by line (4 restorers) X tester (2 cytoplasmic male sterile lines) analysis. The trial comprising 8 hybrids and their parents were laid out in randomized block design with 3 replications and characterized for yield and nine yield component traits. In the present Study, the ANOVA for combining ability revealed significant differences between the treatments (genotype) for all the traits studied and amongst the treatments the mean sum of square (MSS) due to parents showed significant differences for all the traits. The grain yield, grain number per panicle, plant height and days to fifty percent flowering appears to be the key determining traits and showed significant differences for the fines, testers, line X testers. Parents with low X high general combining ability (GCA) effects resulted in heterotic hybrid combination like the IR68291A/IR68749R. Interestingly, we found low X low GCA to give the best heterotic combination, i.e., IR68281A/IR60966R. However, it is worthy to note that the line IR60966R showed non-significant GCA effects for grain yield, hundred grain weight, flag leaf length and grain width while significant but negative GCA effects for grain number per panicle and a low GCA tester IR68281A for all the traits. Perhaps, it implies that the GCA only identifies better parental lots but it will be unwise to discard the low GCA types. Therefore, it can be Concluded that the prediction of heterosis on the basis of GCA of the parents may not always be accurate. Based on the specific combining ability (SCA) effects only three combinations were found to be highly significant for grain yield, i.e., IR58025A/ IR60819R, IR68281A/IR42686R, IR68281A/IR60966R. Such hybrid combinations will be utilized for exploitation of hybrid vigor after assessing their cooking quality features. Heterobeltiosis for yield was positive ranging from 4.1 to 32.2% for six out of eight hybrids. The grain length and width improved for hybrids over the better parents. Predominance of dominant gene action for all the traits studied except for plant height and hundred grain weight thus suggesting that the hybrid breeding must be strongly pursued for the exploitation of the yield advantage over the inbred varieties.