IMMIGRATION OF THE BARLEY MILDEW PATHOGEN INTO FIELD PLOTS OF BARLEY

Immigration of the barley powdery mildew pathogen (Erysiphe graminis f .sp. hordei) into field plots of the spring barley variety Tyra (carry ing the resistance allele Mla1) was investigated. Spores were trapped from the top of the plot canopies, as well as from control plots of wh eat with no barley nearby. Comparison of the frequencies of virulent a nd avirulent single-colony isolates showed that the amount of immigrat ion, relative to the amount of inoculum being produced within the plot , reduced very rapidly, until it could not be detected in the middle o f the growing season (mid-June).