Studying Combining Ability and Heterosis of Important Traits in Tomato (Lycopersicon esculentum Mill.) Using Diallel Crosses

To study the general and specific combining ability and heterosis of six tomato lines, a 6×6 diallel design was used. The parents of the crosses were lines 486 (P1), 208 (P2), 151.6 (P3), Kim (P4), 1010 (P5), and 542 (P6) with different characteristics for yield and other studied traits. All lines were obtained from the Vegetables and Irrigated Pulse Crops Research Department, Seed and Plant Improvement Institute, Karaj, Iran. The parents together with 15 F1 hybrids resulting from their half-diallel crosses (21 genotypes) were planted in a randomized complete block design with three replications in the research farm of Qazvin Agricultural Research Center, in 2019, and fruit yield, number of fruits per plant, fruit weight and total soluble solids (TSS) were measured. The results of the analysis of variance based on second Griffing’s method with the assumption of fixed parents showed that the difference among all genotypes and the difference in general combining ability (GCA) of parents and the specific combining ability (SCA) of hybrids were significant for all studied traits, indicating the role of both additive and non-additive gene effects in the inheritance of traits. Baker's ratio as well as Hung and Holland's ratio for all studied traits were obtained from 0.5 to 1.0, which indicated the role of both additive and non-additive gene effects with the higher contribution of additive effects in controlling all traits. A comparison of parents showed that Kim for fruit yield and number of fruits per plant, line 1010 for fruit weight, and line 468 for TSS had the highest positive and significant GCA. Among the hybrids, hybrid 1010×151.6 for fruit yield and fruit weight, Kim×542 for number of fruits per plant, and Kim×151.6 for TSS had the highest positive and significant SCA. In total, the results of this experiment showed that hybrids 151.6×208 and 151.6×1010 for fruit weight, hybrid 542×1010 for the number of fruits per plant and hybrid 151.6×208 for TSS had the highest positive and significantly better parent heterosis (heterobeltiosis), and were the most valuable hybrids in this experiment, but for fruit weight, only hybrid 468×151.6 had positive and significant mid-parent (standard) heterosis.