Rust resistance in Salix induced by inoculations with avirulent and virulent isolates of Melampsora larici‐epitea

Six Salix clones and four Melampsora larici‐epitea isolates were used in two leaf‐disc inoculation experiments to determine whether disease severity was affected by the presence of both virulent and avirulent rust genotypes. In the first experiment, an equal amount of urediniospores of a virulent isolate and an avirulent isolate was applied simultaneously using four levels of spore suspension. In the second, the willows were inoculated with one isolate first and then, after 3 days, with another using two spore concentrations. In the first experiment, overall rust spore production was reduced by 48.6% in inoculations with mixed inocula compared with that in the inoculations with single virulent isolates. In the second experiment, 20 of the 36 combinations involving pre‐inoculations with avirulent isolates showed significant reduction in spore production. The suppressive effects on rust sporulation were more obvious at the higher inoculum densities and on the clones S. × calodendron and S. × mollissima‘Q83’.