Pathogenic Variation in Some Isolates ofPyrenophora teresf. sp.maculataon Barley

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Abstract
Pathogenic variation in Pyrenophora teres f. sp. maculata, causal organism of Pyrenophora spot blotch of barley (Hordeum vulgare), was evaluated using 20 barley cultivars and 14 fungus isolates from Montana [USA], Morocco, Tunisia, and Turkey. All isolates were avirulent on Unitan, CI 5401, CI 9214, CI 9440, and CI 9776 and virulent on Nupana, Klages, Dekap, Clark, and CI 13727. Tifang, CI 7584, CI 9819, and CI 9825 showed differential reactions between isolates from Montana and those from countries other than the United States. Arimont, Galt, and Steptoe showed differential reactions to both Montana and Mediterranean isolates. A cluster analysis indicated a mean disease rating of 4.3 as the separation point between avirulent and virulent reactions. The frequency of virulence was highest for isolate Turk 74-Pt6 and lowest for Mor 82-1.