VIEW ARTICLE

A Third Infection Type on the Flax Rust Differential Variety Cass. H. H. Flor, Research Plant Pathologist, Crops Research Division, ARS, USDA, and Professor, Department of Plant Pathology, North Dakota State University, Fargo 58102. Phytopathology 60:1691-1692. Accepted for publication 8 June 1970. DOI: 10.1094/Phyto-60-1691.

A collection of flax rust, Melampsora lini (Ehrenb.) Lév., was made in North Dakota in 1968 to which the flax rust differential Cass, monogenic for resistance, had an intermediate reaction (infection type 2). Cass had been either immune (infection type 0) or highly susceptible (infection type 3-4) to all cultures of the flax rust fungus with which it had been tested. The existence of a race inducing a third infection type on a variety monogenic for resistance suggests that genes for pathogenicity, heretofore considered as nonallelic, may occur as multiple alleles.