Cronartium flaccidum fruitbody production on Melampyrum spp. and some important alternate hosts to pine

Four Vincetoxicum species, Paeonia anomala and Melampyrum sylvaticum known to act as alternate hosts for Cronartium flaccidum , and a potential host Melampyrum pratense were inoculated either in vitro or in vivo with various aeciospore sources of C. flaccidum . All fresh C. flaccidum aeciospore sources variably produced uredia or telia on Vincetoxicum hirundinaria , Vincetoxicum mongolicum , Vincetoxicum fuscatum , Vincetoxicum nigrum , P. anomala , nine geographic provenances of M. sylvaticum , and two provenances of M. pratense . This is the first time that C. flaccidum telia were artificially produced on M. sylvaticum and the first time that M. pratense was shown to act as alternate host for C. flaccidum . The results suggest that M. sylvaticum is relatively susceptible to C. flaccidum , whereas M. pratense is almost resistant to this rust. The low host‐specificity of the Finnish population of C. flaccidum was demonstrated, as V. hirundinaria from Italy was susceptible to the rust.