New alternate hosts for the rustsCronartium ribicolaandCronartium flaccidumin Finland

Abstract

We explored the potential of the North European flora and some garden plants growing naturally outside Europe to support a reservoir of pine stem rusts. Live plants and detached leaves of 35 species in 16 families (Solanaceae, Verbenaceae, Grossulariaceae, Paeoniaceae, Balsaminaceae, Gentianaceae, Scrophulariaceae, Loasaceae, Tropaeolaceae, Acanthaceae, Myricaceae, Phrymaceae, Plantaginaceae, Orobanchaceae, Apocynaceae, and Fagaceae) were inoculated in the greenhouse and (or) laboratory with aeciospores of Cronartium ribicola J.C. Fisch. and Cronartium flaccidum (Alb. & Schwein) G. Winter in 2010. Cronartium flaccidum produced uredinia and (or) telia in 14 species in nine families, 11 of which represent new alternate hosts in Finland and nine also elsewhere (excluding Nemesia versicolor and Tropaeolum majus L.): Euphrasia stricta D. Wof. ex J.F. Lehm., N. versicolor E. Mey. ex Benth., Nemesia strumosa Benth., Verbena × hybrida Voss., Verbena officinalis L., Veronica longifolia L., Impatiens glandulifera Royle, T. majus, Loasa triphylla Juss., Asclepias incarnata L., and Bartsia alpina L. Cronartium ribicola formed fruitbodies in nine species and cultivars in five families, five of which are new alternate hosts for this species in Finland and also elsewhere: Mentzelia lindleyi Torr. & A. Gray, A. incarnata, B. alpina, L. triphylla, and T. majus. Both species of Cronartium infected four alternate hosts, each in its own family. The alternate host range of each Cronartium was wider than expected and wider than that previously described. In local natural forests, Euphrasia , Veronica , and Bartsia (in northern Finland) are potential hosts that are common and may be able to spread these rusts. The recently established ornamental I. glandulifera could provide the means to spread C. flaccidum to Scots pine ( Pinus sylvestris L.) in southern Finland, and species of Mentzelia may be important for the spread of C. ribicola.