General and specific combining ability for yield-related traits in watermelon

Estimates of combining ability are useful in determining the value of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) lines in producing new hybrids with high yield and better quality. This research was conducted to estimate the general combining ability (GCA), specific combining ability (SCA), and heterosis for five inbred lines chosen for watermelon breeding at the University of Guilan, Iran. Analysis of variance indicated significant differences among hybrids for fruit weight and the number of lateral branches per plant. The GCA and SCA effects were significant for fruit weight and the number of lateral branches, which indicates the existence of both additive and dominance effects in controlling these two traits. The low narrow sense heritability indicated the smaller impact of additive gene action on fruit weight and the number of lateral branches in watermelon. However, broad sense heritability was high for fruit weight (0.69) and the number of lateral branches (8.88). The large gap between the broad sense heritability and narrow sense heritability indicated the importance of dominance effects in controlling the fruit weight and the number of lateral branches compared to additive effects. These results justify the development of hybrid varieties to exploit the dominance genetic effects in watermelon. The highest fruit weight and the number of lateral branches belonged to the S × Red cross. The highest SCA for the fruit weight was associated with the cross An × S. The cross S × Red had the highest SCA for the number of lateral branches. The high-parent heterosis was also higher in the cross S × Red for these traits. In conclusion, the hybrid S × Red may be proposed for the production of a hybrid variety in watermelon. However, crossing among various genotypes to produce new inbred lines seems necessary for the hybrid breeding program of watermelons in Iran.