THE RELATIVE PREVALENCE OF SPECIALIZED FORMS OF PUCCINIA CORONATA THAT OCCUR ON RHAMNUS CATHARTICA IN CANADA

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Abstract
Surveys were made during the period 1947–1951 to determine the prevalence and distribution of the specialized forms (formae speciales) of Puccinia coronata Corda which occur on Rhamnus cathartica L. in Canada. From 96 aecial collections obtained in Manitoba and in Eastern Canada on R. cathartica, three distinct forms of P. coronata were isolated. Two of these, f. sp. avenae and f. sp. festucae, had been isolated previously in both Europe and North America. The third form, which could not be identified with any previously described form, was pathogenic on many species of wild and cultivated grasses, as well as on many varieties of barley and rye, but was nonpathogenic on oats. It is given the designation P. coronata f. sp. secalis f. sp. nov. The uredial stage of f. sp. secalis is much darker in color than the corresponding stage of the other two forms and it can be distinguished from them quite readily. The forms avenae and secalis occurred in Manitoba and Eastern Canada, while the form festucae was found in Eastern Canada only. In Eastern Canada the forms avenae, secalis, and festucae, in the order named, comprised 60.6, 36.6, and 2.8% of the isolates. In Manitoba, the form avenae comprised 16 and the form secalis 84% of the isolates.

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