Reaction of Cotton Cultivars and an F₂ Population to Stem Inoculation with Isolates <i>Verticillium dahliae</i>

Abstract Four Verticillium dahliae isolates (V76, TS‐2, PH, and V44) were used in screening four cotton cultivars (Pima S‐7, Acala Prema, M‐315 and Acala 44). Pima S‐7 and Acala Prema gave the highest resistance reactions and Acala 44 was the most susceptible. Isolate V76 of V. dahliae was the most virulent. An interspecific cross between the resistant cv Pima S‐7 ( Gossypium barbadense ) and the susceptible cv. Acala 44 ( G. hirsutum ) was made and the F 2 population phenotyped for Verticillium wilt effect. Phenotyping of plant reaction to the disease was quantified by using a set of six growth parameters (number of healthy leaves, number of nodes, leaf weight, stem weight, leaf to stem ratio, and total shoot weight) measured 3 weeks after inoculation. The F 2 phenotypic distribution of these parameters suggests that distribution is towards resistance and polygenic. Transgressive segregation also was observed. The number of healthy leaves and total shoot weight were found to be the best indicators of resistance. Results obtained in this study will be useful to quantify resistance to V. dahliae and identify the best parameters to phenotype in genetic studies.