Evaluation of Dasypyrum villosum Populations for Resistance to Cereal Eyespot and Stripe Rust Pathogens

Dasypyrum villosum Candargy (syn. Haynaldia villosa) is a cross-pollinating, diploid (2n = 2x = 14) annual species that belongs to the tribe Triticeae (18). It is native to Southern Europe and West Asia, especially the Caucasuses (14), and grows under conditions unfavorable to most cultivated crops. The genome of D. villosum, designated V by Sears (40), is considered an important donor of genes to wheat for improving powdery mildew resistance (6,13), take-all (39), eyespot (35,43), and plant and seed storage protein content (13,15,41). D. villosum has been hybridized with diploid, tetraploid, and hexaploid species of Triticum (3,6,15,19,21,38,40), and six of the seven D. villosum chromosomes have been added disomically to a hexaploid wheat background (40). Interspecific hybridization reveals very little homology between wheat and D. villosum and, until recently, it was believed that homologous gene transfer was not possible because V genome chromosomes do not pair well with wheat chromosomes (19,40). However, Chen et al. (6) have successfully recovered genotypes containing spontaneous translocations between wheat and D. villosum chromosome 6V with resistance to powdery mildew. Pollen fertility appears to be the main problem in crosses performed between D. villosum and wheat (4). F1 plants are completely male sterile and partially female fertile (28). However, the extra effort required in gene transfer from D. villosum to wheat for eyespot resistance is warranted because of the small pool of resistance genes available to breeders (24). Eyespot is one of the most economically important diseases of wheat in the U.S. Pacific Northwest and many other temperate wheat-growing areas in the world (23,44). The disease is caused by Pseudocercosporella herpotrichoides (teleomorph Tapesia yallundae) and affects the stem base of wheat and other grasses, causing weak stems, lodging at the seed filling stage, and production of grainless white heads (23). The disease has been controlled primarily with fungicides, but the widespread occurrence of fungicide resistance in the pathogen (35) has encouraged development of resistant cultivars. Breeders have successfully improved resistance in some commercial cultivars (1,2,16,25,32), but the continuing effort to improve resistance has been slow, because neither of the two known resistance genes offer complete resistance (24). One of the genes, Pch1, originated from the goat grass species Aegilops ventricosa, and is located on chromosome 7DL (17,20,29,42). The other gene, Pch2, comes from wheat cv. Cappelle Desprez and is located on chromosome 7AL (12,26). Pch1 is the most widely utilized source of eyespot resistance in breeding programs, primarily because it is more effective than Pch2. D. villosum is one of the wild wheats that was initially reported by Sprague (43) to be resistant to eyespot, but has been used little since that report. Recently, Murray et al. (35) located a new resistance gene for eyespot on chromosome 4V of D. villosum. Characterization and transfer of these new genes into hexaploid wheat may provide a more complete resistance to eyespot by pyramiding resistance genes into a single cultivar. Stripe rust, caused by Puccinia striiformis f. sp. tritici, is also an economically important disease of wheat in the Pacific Northwest and worldwide (27). Stripe rust is principally a destructive disease of wheat during the winter and early spring, causing up to 90% yield loss when the environment is favorable (37). On average, stripe rust epidemics occur three out of four years in the Pacific Northwest (10). Cultivars with both race-specific and racenonspecific (adult plant) resistance are the most effective control method (10,36), despite the fact that the pathogen can overcome race-specific resistance in a few years. Therefore, it is important to identify new resistance sources in the seedling stage for specific resistance to reduce the amount of damage caused by the rust during the seedling stages. The objective of this study was to identify D. villosum accessions resistant to the eyespot and stripe rust pathogens for potential use as sources of genes for resistance to these important diseases of wheat.