Mapping a gene conferring resistance to Pseudocercosporella herpotrichoides on chromosome 4V of Dasypyrum villosum in a wheat background Ahmet Yildirim, Stephen S. Jones, and Timothy D. Murray Abstract: The objectives of this study were to map and tag the previously undescribed eyespot resistance gene PchDv on chromosome 4V of Dasypyrum villosum in a wheat background. The 82 F 2 plants used for mapping were produced from a cross between a susceptible wheat ‘Yangmai–5’ (4V(4D)) substitution line and a resistant wheat ‘Chinese Spring’ disomic addition line of chromosome 4V of D. villosum. Segregation for resistance and susceptibility among F 2 plants was 3:1, indicating that resistance was controlled by a single dominant gene. PchDv mapped to the distal part of chromosome 4V and was bracketed by two RFLP markers, Xcdo949 and Xbcd588, in a 33-cM interval. This distance could not be reduced, owing to a lack of polymorphic loci in this region. Theoretically, double recombination in this region occurs in 3.3% of the individuals; therefore, 96.7% of the selected genotypes would have PchDv, with simultaneous selection for both flanking markers. Double recombination between the flanking markers was observed in 2 out of 82 (2.4%) F 2 individuals. Key words: eyespot, Haynaldia villosa, Triticum aestivum, RFLP, wild wheat. Résumé : L’objectif de cette étude était de déterminer l’emplacement chromosomique et de marquer un gène de résistance au piétin-verse qui n’avait pas encore été décrit, PchDv, sur le chromosome 4V du Dasypyrum villosum dans un fond génétique de blé. Les 82 plantes F 2 employées pour la cartographie ont été produites par croisement entre une lignée de substitution sensible du blé ‘Yangmai–5’ (4V(4D)) et une lignée d’addition résistante disomique du blé ‘Chinese Spring’ portant le chromosome 4V du D. villosum. Un ratio de ségrégation de 3 résistantes : 1 sensible parmi les plantes F 2 a révélé que la résistance était sous le contrôle d’un seul gène dominant. Le gène PchDv a été assigné à un intervalle de 33 cM sur le partie distale du chromosome 4V entre les marqueurs RFLP Xcdo949 et Xbcd588. La distance n’a pu être réduite davantage en raison de l’absence de loci polymorphes dans cette région. Théoriquement, des doubles recombinaisons dans cette région surviennent dans 3,3% des individus, ainsi 96,7% des génotypes sélectionnés à l’aide des deux marqueurs posséderont le gène PchDv. Parmi les 82 plantes F 2 examinées, deux double recombinants (2,4%) ont été observés. Mots clés : piétin-verse, Haynaldia villosa, Triticum aestivum, RFLP, blé sauvage. [Traduit par la Rédaction] Introduction Eyespot, caused by the facultative parasite Pseudocerco- sporella herpotrichoides (Fron.) Deighton, is an economically important disease of wheat in the U.S. Pacific Northwest and many other winter wheat growing areas of the world (Johnson 1992; Wiese 1991). Previously, there were only two resistance genes known for eyespot. The first, Pch1, was transferred from Aegilops ventricosa (Dosba and Dossinault 1973) and is used extensively in breeding programs because of tightly linked isozyme (McMillin et al. 1986) and RFLP markers (Chao et al. 1989). Pch1 alone does not provide complete resistance to the disease, but is more effective than the second gene, Pch2. Pch1 occurs on the long arm of chromosome 7D and, recently, Pch2 was mapped to the long arm of chromosome 7A (de la Peña et al. 1997). Occurrence of new pathotypes of the pathogen increases the possibility of circumventing existing resistance (Jones et al. 1995). Dasypyrum villosum (2n = 14, genome VV), a distant rela- tive of wheat, was identified as being highly resistant to eye- spot, and a resistance gene(s) was located in a chromosome 4V addition line (Murray et al. 1994). Subsequently, it was deter- mined that a disomic wheat – D. villosum 4V(4D) substitu- tion line was susceptible to eyespot (Yildirim et al. 1997; A. Yildirim, unpublished data). The existence of the suscepti- ble 4V substitution line makes it possible to map the resistance gene in a wheat background, which is advantageous, because the chromosome is homozygous in a disomic state. Dasypyrum villosum is a cross-pollinating diploid species (Frederiksen Genome, 41: 1–6 (1998) Corresponding Editor: J.P. Gustafson. Received May 28, 1997. Accepted September 16, 1997. A. Yildirim 1 and S.S. Jones. 2 Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164–6420, U.S.A. T.D. Murray. Department of Plant Pathology, Washington State University, Pullman, WA 99164–6430, U.S.A. 1 Present address: Gaziosmanpasa University Ziraat Fakültesé, 60110 Tokat, Turkey. 2 Author to whom all correspondence should be addressed (e-mail: joness@wsu.edu). 1 © 1998 NRC Canada