Rust resistance inSalixtoMelampsora larici-epitea.

A total of 174Salix(willow) clones belonging to 57 species and 14 interspecific hybrids were inoculated with seven pathotypes ofMelampsora larici-epiteausing the leaf disc method. Infection types were scored based on the uredinial pustule area data and the inoculum density. A close correlation (R2 = 0·82) was found between the average pustule area and the average number of spores produced. Most of the willows were also assessed in the field for rust in 1999. Most willow clones belonging to the species native to western Europe were infected by the rust. In inoculation experiments, uredinia developed on 46S. viminalisclones, out of a total of 47. In the field, all theS. viminalisclones were infected by rust. Within the subgenusVetrix, eight out of the 17 willow species that originated from North and South America produced rust pustules in inoculation experiments. Of these,S. pellitawas most susceptible.Salix irrorataandS. lasiolepsisvar.bracelinaeproduced well developed pustules after inoculation but no rust infections were detected in the field. In both leaf disc tests and field assessments, no rust infections were found onS. candida,S. cordata,S. drummondiana,S. eriocephala,S. hookeriana,S. houghtonii,S. humilis,S. rigidavar.mackenzianaandS. syrticola. Of 12 species of subgenusVetrixnative to northeast Asia and Japan, onlyS. kochianawas susceptible both in inoculation tests and in the field.Salix rossicaproduced no symptoms in leaf disc tests but showed low levels of infection in the field. The maximum infection type scores in leaf disc tests were highly significantly correlated with field disease severity scores (Spearman rank correlation coefficient was 0·76,P < 1 × 10−10). [ABSTRACT FROM AUTHOR]