Summary Experiments were carried out to determine the relationship between the varieties of Puccinia coronata Corda previously isolated in Great Britain and the two species of Rhamnus, R. Frangula and R. cathartica, which are the alternate hosts of the rust in this country. The experiments included: (a) the inoculation of seedling plants of the Rhamnus species with sporidia from germinating teleutospores of the different varieties; and (b) the inoculation of a number of grasses with aecidiospores collected in the field on the two species of Rhamnus. The varieties were found to show a considerable degree of specialization in their relation to the alternate hosts, vars alopecuri, arrhenatheri, avenae, festucae, holci and lolii producing aecidia on R. cathartica only and var. calamagrostidis on R. Frangula only. The difference in aecidial host relationship of the varieties is not considered to be an adequate criterion for species differentiation, and it is suggested that the use of the names Puccinia coronata Kleb. and P. coronifera Kleb. (P. Lolii Niels.) be discontinued and the rust be designated by the original name P. coronata Corda. The pathogenicity of the varieties was not altered appreciably by passage through the alternate host and the varieties did not appear to hybridize readily.
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M. R. BROWN (1938) studied this question.