UROMYCES STRIATUS SCHROET. IN ONTARIO

Abstract

Large stands of Euphorbia cyparissias L. in Ontario supporting aecia of Uromyces striatus Schroet. presented an opportunity for the author to study this stage of the rust hitherto little known in North America since its discovery here in 1947. The mycelium was found to be systemic and perennial and the aeciospores capable of infecting many species of Medicago and some yellow-flowered species of Trifolium. Pisum sativum was just slightly susceptible. Both diploid and tetraploid nuclear conditions of E. cyparissias have been found rusted and E. esula, long suspected as a host in Europe, has also been found rusted and the connection to Leguminosae shown by inoculation. Specimens resulting from inoculations (109) and from field collections from Canada (33), United States (18), and Europe (13) were identical in spore morphology. This, plus susceptibility of Leguminosae from Europe to the inoculum from Ontario, supports the suggestion that the rust was introduced to North America from Europe. It is further suggested that U. striatus was introduced on either or both alternate hosts independently. The common occurrence of telia is recorded and the fungus is redescribed.