Physiologic Races of the Brown Rust of Brome Grasses

A number of cultures of the brown rust of Brome grasses havebeen isolated and maintained as single-spore strains. By theirinfection reactions on a representative selection of Brormusspp. at least five physiologic races have been characterized.Two of these have host-ranges confined to a single section ofthe genus, but others have a much wider host-range within thegenus. The uredospore stage of all was identical. Studies ofthe teleutospores have been limited and knowledge of the speciesof rust involved is incomplete. All belong to the group-speciesPuccinia dispersa Erikss. & Henn.; the species P. brominaErikss. and P. symphyti-bromorum Müller were included amongthe cultures studied, possibly also P. bromi-maximi Guyot. Ina large series of inoculations, over a period of in all 14 years,all physiologic races have been remarkably stable in their infectiontypes and host-range, and no confirmation of Marshall Ward's‘bridging-host’ theory has been obtained. Cultivationof two physiologic races for 164 generations on Bromus arduennensis,a species considered by Ward to have special significance asa bridging-host, induced no changes in their host-range.