Estimation of combining ability and heterosis in some Iranian lettuce lines using diallel crosses analysis

In order to estimate heritability, heterosis, general and specific combinability for traits of leaves number per plant, number of days to first flowering, plant fresh weight, stem fresh weight and the length of the flowering stalk, seven local populations of Iranian lettuce (‘Siahe Dezful’, ‘Gorgan’, ‘Varamin’, Jahrom and ‘18’, ‘21’, ‘27 Mazandaran’) were crossed using a complete diallel crosses design. (These lines were obtained during several generations of selfing in their province). Overall, 49 genotypes including Parents and all possible hybrids were evaluated in a randomized complete block design with three replications. The first method of Griffing’s, Model I was used to estimate the combinability. Analysis of variance revealed high significant differences among F1 hybrids and their parentes for all the studied traits. Therefore analysis of combinabilities showed that general combining ability (GCA) in all the studied traits were greater than specific combining ability (SCA), indicating the importance of additive genes action in controlling these characters than non- additive effects.  High narrow sense heritability (h2ns) for the traits including the length of the flowering stalk and plant fresh weight (0.89 and 0.74, respectively) indicated low effects of environment on the expression of those traits and increased role of additive gene effects. High heterosis effect over the better parent was found for plant fresh weight (11.9 percent) and leaves number per plant (12.42). Results of this research can help to implement more effective and efficient activities in lettuce.