Response of Durum Wheat Kernels and Leaves at Different Growth Stages to Pyrenophora tritici-repentis . M. R. FERNANDEZ, Research Station, Agriculture and Agri-Food Canada, P.O. Box 1030, Swift Current, Saskatchewan, Canada S9H 3X2. J. M. CLARKE, and R. M. DePAUW, Research Station, Agriculture and Agri-Food Canada, P.O. Box 1030, Swift Current, Saskatchewan, Canada S9H 3X2. Plant Dis. 78:597-600. Accepted lor publication 15 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0597.

Fourteen durum wheat genotypes were evaluated for the reaction of leaves at different growth stages and kernels to Pyrenophora tritici-repentis. Plants were artificially inoculated with P. tritici-repentis at the two-leaf stage and after emergence of the flag leaf, and were rated for tan spot reaction by percent leaf area with symptoms and lesion type or length. At two locations in southern Saskatchewan, the same genotypes were rated in the field for leaf spots at late milk to early dough in 1991 and 1992. There was no correlation among trials in percent leaf area with symptoms at the seedling stage. Lesion type was considered the best method to determine tan spot reaction at the seedling stage. Lesion length and percent leaf area with symptoms on the Hag leaf were correlated among trials. Lesion length was correlated with percent area with symptoms on the flag leaf and was considered Ihe best method for rating tan spot reaction in adult plants. Percent leaf area with symptoms at the seedling stage was not correlated with that on the flag leaf or with field leaf spot ratings. Most lesions on field plants were attributed to P. iritici-repentis. Field leaf spot ratings were correlated with both percent leaf area with symptoms and lesion length on the flag leaf of artificially inoculated plants. Percent incidence of red smudge in kernels of plants artificially inoculated with P. iritici-repentis al the milk lo early dough stage was not correlated, or was negatively correlated, with tan spot reaction at the seedling or adult stages, and with field leaf spot ratings. In the durum wheat genotypes tested, different resistance mechanisms to P. tritici-repentis seemed to be operating in different organs of the plant, and resistance to tan spot observed at the adult stage was not expressed at the seedling stage.