A METHOD OF INOCULATING ADULT WHEAT PLANTS WITH UREDIOSPORES OF PUCCINIA-STRIIFORMIS TO MEASURE COMPONENTS OF RESISTANCE

In preliminary experiments, six methods of inoculating a small section of wheat leaves with stripe rust urediospores were compared. The best method was to place small agar blocks preinoculated with urediospores of Puccinia striiformis on a leaf. Components of resistance could be easily measured using this inoculation method. High spore densities were needed to obtain good infection. For successful infection of 90% of the leaves, at least 200 spores per square centimeter should be applied. To achieve at least 15 infection per inoculated leaf, at least 485 spores per square centimeter of leaf were needed. Latency period, infection frequency, and length of infection were not significantly affected by the leaves or inoculation position on leaves. Latency period was the most precise component of resistance because of its low coefficient of variation. In a case where large numbers of genotypes have to be screened, infection length might be preferred because it was less time-consuming to measure than latency period.