Selection influences heritability estimates and variance components for anthracnose resistance in populations derived from an intraspecific cross of tomato

Genetic characterization of anthracnose resistance in tomato (Lycopersicon esculertum Mill,) caused by Colletotrichum coccodes (Wallr,) Hughes was acc omplished using populations developed from crosses between the anthracnose susceptible cultivar US28 and three resistant breeding lines (115-4, 625-3, and 88B147) that varied in their degree of anthracnose resistance and rela tive stage of adaptation for commercial use. These lines were of common par ental lineage with resistance derived from the small-fruited L. esculentum USDA PI272636. Anthracnose lesion diameters and fruit weight were measured in puncture inoculated fruit of parental, F-1, F-2, and backcross generatio ns within each cross. Correlation coefficients between fruit size and lesio n diameter were low and generally nonsignificant, Estimates of broad and na rrow sense heritabilities for resistance were moderate and declined as rela tive anthracnose susceptibility of the resistant parent increased coinciden t with increasing horticultural adaptation. A simple additive dominance mod el, m[d][h], was adequate to explain the genetic variance for anthracnose r esistance in all crosses. Genetic variance for anthracnose resistance was p rimarily additive, The minimum number of effective factors or loci conditio ning anthracnose resistance declined during attempts to transfer high level s of resistance from PI 272636 into adapted breeding lines.