New alternate hosts for Cronartium spp.: Odontites, Euphrasia, Rhinanthus and Papaver

Abstract

AbstractSusceptibility of 13 plant species to Scots pine blister rust, Cronartium flaccidum, or white‐pine blister rust, Cronartium ribicola, was tested in Finland. The test species belonged to 10 genera in eight plant families, and they were inoculated in the laboratory or in the glasshouse. After 8 weeks of incubation, C. flaccidum sporulated on five species and provenances in the glasshouse and six species in the laboratory. After similar incubation, C. ribicola sporulated on one species in the glasshouse and two species in the laboratory. Cronartium ribicola formed uredinia and telia on Euphrasia nemorosa in the glasshouse and uredinia on E. nemorosa and Ribes nigrum in the laboratory. Cronartium flaccidum produced uredinia and telia on Odontites verna (two provenances), E. nemorosa and Euphrasia stricta both in the glasshouse and in the laboratory, on Papaver rhoeas in the glasshouse, and on Rhinanthus serotinus, Impatiens parviflora and Paeonia lactiflora in the laboratory. Rhinanthus serotinus, O. verna, I. parviflora and P. rhoeas are new alternate hosts for C. flaccidum, and for the first time, species of Odontites and Papaver were confirmed by molecular methods as alternate hosts for the rust. Cronartium ribicola was reported to sporulate on E. nemorosa for the first time. In conclusion, hemiparasitic genera of the family Orobanchaceae contain several forest species that are susceptible to C. flaccidum, although single highly resistant species also occur in these genera. Similarly, several genera of Orobanchaceae contain single species that are susceptible to C. ribicola, although most of the species in this family are highly resistant to the rust. In a severely damaged Scots pine stand in northern Finland, C. flaccidum was found to sporulate commonly on Melampyrum sylvaticum and E. stricta, and rarely on Rhinanthus minor. This is the first report of natural sporulation of C. flaccidum on Rhinanthus in its natural habitat.