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Role of Host Sensitivity to Ptr ToxA in Development of Tan Spot of Wheat

April 2003 , Volume 93 , Number  4
Pages  397 - 401

T. L. Friesen , S. Ali , S. Kianian , L. J. Francl , and J. B. Rasmussen

First, second, fourth, and fifth authors: Department of Plant Pathology; and third author: Department of Plant Sciences, North Dakota State University, Fargo 58105

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Accepted for publication 24 October 2002.

Pyrenophora tritici-repentis race 2 produces Ptr ToxA, a host-selective toxin previously described as a pathogenicity factor for tan spot on wheat. The objective of this research was to evaluate the role of host sensitivity to toxin, conditioned by a single dominant gene on chromosome 5BL, in the disease development by race 2. An F2-derived F6 recombinant inbred population of 108 wheat lines, produced from crosses of toxin-sensitive, disease-susceptible cv. Kulm with the toxin-insensitive, disease-resistant cv. Erik segregated 1:1 for toxin reaction. However, the population was skewed toward resistance to race 2 of the fungus. Toxin reaction accounted for 24.4% of the genetic variance for disease. Heritability estimates suggested the presence of four to five genes that influence disease reaction in the population. Toxin-insensitive mutants, previously derived Kulm, were susceptible to race 2, although disease developed more slowly on the mutants than it did on the wild-type Kulm. The data indicate that sensitivity to Ptr ToxA influences disease severity in some host genotypes without defining susceptibility.

© 2003 The American Phytopathological Society