Genetic and phenotypic characterization of Botrytis calthae

Botrytis calthae is a necrotrophic plant pathogen, closely related to the ubiquitous broad host range fungus Botrytis cinerea , but highly host specific. Botrytis isolates from lesions of Caltha palustris grown at different locations were classified with genetic markers as either B. calthae or Botrytis pseudocinerea , or less frequently as B. cinerea . A PCR‐based identification of B. calthae was developed. Seven haplotypes of B. calthae could be distinguished. Compared to B. cinerea , mycelium growth of B. calthae was similar, but conidiation less abundant, and sclerotia formation was only partially repressed by light. Conidia of B. calthae germinated more slowly, and showed a highly acidic optimum ( pH 2·5) compared to B. cinerea conidia ( pH 5·3). All B. calthae isolates were sensitive to common anti‐ Botrytis fungicides, but showed partial resistance to the succinate dehydrogenase inhibitors boscalid, fluopyram and carboxin. Infection experiments revealed a weak capability of B. calthae to induce necrotic lesions on plants that are hosts for B. cinerea . On C. palustris leaves, B. calthae induced similar lesions to B. cinerea . These data provide a basis for comparative molecular investigation of the physiology and host specificity of B. calthae and closely related Botrytis species.