Evaluation of Parthenium Species for Resistance to Verticillium dahliae. P. C. Cheo, Chief Plant Pathologist, Los Angeles State and County Arboretum, Arcadia, CA 91006. Colette M.-S. Beaupre, Research Assistant, Research Division, Los Angeles State and County Arboretum, Arcadia, CA 91006. Plant Dis. 65:658-661. Accepted for publication 8 December 1980. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-658.

Eight strains of Verticillium dahliae, six of which were isolated from hosts other than guayule (Parthenium argentatum), induced wilt in guayule. Diploid plants wilted faster after inoculation than tetraploid plants. Younger seedlings were more susceptible to infection than older ones. Guayule was more susceptible to infection by V. dahliae than were four other Parthenium species tested. P. fruticosum was susceptible to S_T-1, a cotton-defoliating strain, but tolerant to all other strains, including two isolated from guayule in the field. P. tomentosum var. stramonium, P. incanum, and P. confertum var. lyratum were tolerant to all the strains used.