Pathogenicity on Wheat ofPyrenophora tritici-repentisIsolated fromBromus inermis

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Abstract
Twenty-seven isolates of Pyrenophora tritici-repentis from smooth bromegrass, an alternative host, were tested for virulence on wheat and smooth bromegrass. Detached seedling leaves of wheat and smooth bromegrass were inoculated to compare bromegrass isolates with wheat isolates in individual tests involving five wheat and three smooth bromegrass cultivars. Leaves were visually assessed for percentage of necrosis and lesion length. Although all isolates caused symptoms on wheat and smooth bromegrass, the smooth bromegrass isolates varied in their ability to cause disease symptoms on wheat. Most smooth bromegrass isolates caused disese symptoms on wheat similar to those caused by wheat isolates, but some caused fewer disease symptoms than the wheat isolates. Smooth bromegrass isolates selected for high and low virulence levels in the detached leaf tests were compared in two additional detached leaf inoculations and in glasshouse inoculations with whole plants. The two additional detached leaf inoculations and the glasshouse inoculations with whole plants confirmed the results obtained with the initial detached-seedling leaf inoculations. In both types of inoculations, bromegrass isolates of P. tritici-repentis had virulence levels comparable to those of wheat isolates.