Evaluation of <i>Frankia</i> strains isolated from provenances of two <i>Alnus</i> species

Using the OsO 4 isolation method, more than 200 Frankia strains were obtained from 27 provenances of the two alder species represented in Quebec, i.e., Alnus crispa (Ait.) Pursh. and Alnus rugosa (Du Roi) Spreng. The Frankia isolates were evaluated for morphological characteristics, infectivity, and efficiency. Variations in these factors were noted between provenances and also between isolates from a single provenance. The distribution of sporulating (Sp + ) and nonsporulating (Sp − ) type isolates was found to be related to host plants and provenance. The sporulating or nonsporulating endophytic character was found to significantly affect efficiency. This endophytic character was recognized as one of the valid criteria that should be used in the awaited species definition in the genus Frankia.