VIEW ARTICLE

Segregation of Pathogenicity Types and Host-Specific Toxin Production in Progenies of Crosses between Races T and O of Helminthosporium maydis (Cochliobolus heterostrophus). O. C. Yoder, Department of Plant Pathology and Plant Breeding & Biometry, Cornell University, Ithaca, N.Y. 14853; V. E. Gracen, Department of Plant Pathology and Plant Breeding & Biometry, Cornell University, Ithaca, N.Y. 14853. Phytopathology 65:273-276. Accepted for publication 27 September 1974. DOI: 10.1094/Phyto-65-273.

Randomly isolated ascospore progeny of certain crosses between race T and race O of Helminthosporium maydis segregated in a 1:1 ratio for race T-type and race O-type pathogenicities. Progeny of other crosses segregated in a ratio of approximately seven ascospores with race O-type pathogenicity to one ascospore with race T-type pathogenicity, suggesting either that more than one gene controls race T-type pathogenicity, or that segregation of a single gene can be complex in certain crosses. In all cases involving cultures derived from 202 ascospores isolated from race T × race O and race T × race T crosses, race T-type pathogenicity was associated with ability to produce T-toxin. This association suggests that T-toxin production is required for race T-type pathogenicity.