Evaluation of Combining Ability in Rice Cultivars Based on Second and Fourth Griffing Methods

Six rice cultivars were crossed in half diallel design to evaluate their GCA and SCA in 2005. In the following year, parents and their progenies were grown in a randomized complete block design with three replications, and 10 traits were measured. The analysis of variance showed significant differences (p≤0.01) between cultivars. Furthermore, general combining ability (GCA) and specific combining ability (SCA) for parents and hybrids were significant. Therefore, additive and non-additive gene effects on controlling traits were demonstrated. According to the analysis based on the second and fourth Griffing methods, additive gene effects were more than non-additive gene effects on controlling growth period, plant height, panicle length, number of panicles/plant and brown rice length, while other studied traits were more controlled by non-additive gene effects. Comparison of the second and fourth Griffing methods showed that the proportions of additive and non-additive variances in two methods were different. Moreover, GCA and SCA resulting from the two methods for several traits such as vegetative and productive growth period, plant height, number of filled grains/panicle and grain yield were significant. Therefore, it could be concluded that using parental generations in the second Griffing method may cause biased estimate of the GCA and SCA variances. Thus, using the fourth Griffing method is more suitable than the other methods in providing time, cost and facilities, and is recommended as an applicable method.