Tomato (Lycopersicon esculentum Mill.) genotypes evaluated for early blight [Alternaria solani (Ellis & Martin) Jones and Grout] resistance included five tolerant breeding lines, a susceptible cultivar, and seven hybrids among them. Three of the genotypes (`Castlejay', NC EBR-2, and 87B187) were crossed in a diallel mating design to estimate general combining ability and specific combining ability for the resistance trait. Parental, F1, F2, and backcross generations of the family Cl943 x `Castlejay' were evaluated for resistance and included in generation mean analysis. Hybrid means for area under the disease progress curve were not significantly different from respective midparent values, indicating additive genetic control. Diallel and generation mean analyses also detected significant additive genetic effects. Epistasis was present in the Cl943 × `Castlejay' family.
A 6-parent diallel was used to study combining ability and type of gene action contributing to resistance in tomato (Lycopersicon esculentum Mill.) to anthracnose caused by Colletotrichum dematium (Pers. ex Fr.). The 6 parents, one set of F1, hybrids, and 5 selected reciprocal crosses were grown at 2 locations. Ripe fruit were harvested, puncture-inoculated with the pathogen, and subsequently evaluated for resultant lesion diameter. No reciprocal effects were found at either location for the 5 crosses studied. The analysis of variance for parent and F1 hybrid performance revealed a genotype × location interaction. Combining ability analysis based on the F1 hybrids alone indicated a significant general combining ability (GCA) effect. The specific combining ability (SCA) and GCA × location interaction mean squares were smaller than the GCA value but were still significant. Differential performance over locations of the hybrids of one line was primarily responsible for the GCA × location interaction. Analysis of variance and covariance of parental arrays indicated partial dominance in the direction of susceptibility. Narrow sense heritability for the trait was 70% over both locations.
Six inbred tomato (Lycopersicon esculentum Mill.) genotypes and 13 hybrids among them were evaluated at two locations for resistance to early blight (Altemaria solani). The breeding lines 71B2, C1943, and NC EBR-1 were the most resistant, while ‘Castlejay’ was consistently the most susceptible. Hybrid means for area under the disease progress curve (AUDPC) generally were intermediate to their parental values, indicating quantitative genetic control. Five of the parents were included in a diallel mating design to obtain estimates of general combining ability (GCA) and specific combining ability (SGA) for the resistance trait. Both GCA and SCA were highly significant; the GCA component accounted for 88.2% of the genotypic variation.