COMPARISON OF RESPONSES TO FLORET AND SEEDLING INOCULATION IN WHEAT USTILAGO-TRITICI AND BARLEY U-NUDA COMBINATIONS

The floret and seedling methods for inoculating wheat and barley with Ustilago tritici and U. nuda, respectively, were optimized and then compared. Floret inoculation gave higher infection levels than did seedling inoculation, especially for wheat, but problems of plant mortality and standardization of tissue age were greater with the former method. Floret inoculation identified wheat and barley varieties exhibiting embryo resistance (class 1 or 2 resistance) or seedling resistance (class 3), but only class 3 wheat and barley varieties (and one class 2 wheat variety) were resistant to seedling inoculation. Using near-isogenic wheat lines expressing different levels of partial resistance to floret inoculation, positive correlations were obtained between percentage infection levels resulting from the two inoculation protocols. In addition, race-specific host-pathogen interactions such as hypersensitivity and partial smutting were expressed following both floret and seedling inoculation, indicating that these interactions operate in the developing plant. The potential value of the seedling inoculation method in fundamental and applied research into the cereal-loose smut interaction is discussed.