Genetic analysis of Verticillium wilt tolerance in cotton using pedigree data from three crosses

Three crosses and descendant generations were used in a field study of the inheritance of tolerance to Verticillium wilt, caused by Verticillium dahliae Kleb., in upland cotton (Gossypium hirsutum L.). The tolerant cultivar 'Acala SJC-1' was crossed to more susceptible parents, breeding line S5971 and cultivars 'Acala 4-42' and 'Deltapine 70'. Seven generations were evaluated for each cross: the two parents (P1 and P2), F1; F2, F3, and reciprocal backcrosses (B1 and B2). The genetic control of tolerance in these crosses appears to involve more than one gene, based on an unsatisfactory fit to expected phenotypic distributions for the generations under a single-locus model. An analysis of generation means indicated that pooled additive and pooled dominance effects over loci were adequate to explain the variation among generations for crosses of SJC-1 X S5971 and SJC-1 X DPL70. Tolerance in these crosses appeared to be controlled by recessive factors. For the SJC-1 X 4-42 cross, an adequate fit to a digenic epistatic model was not possible, and none of the genetic parameters except the F2 mean were significant. Heritabilities for tolerance to Verticillium wilt, determined from regressions of F3 progeny on F2 parents for the crosses of SJC-1 X S5971 and SJC-1 X DPL70, ranged from 0.12 to 0.28. Therefore, individual plant selection for improved tolerance is expected to be inefficient.