Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2003
Publication Date: 7/1/2003
Citation: KOLMER, J.A., LONG, D.L., KOSMAN, E., HUGHES, M.E. PHYSIOLOGIC SPECIALIZATION OF PUCCINIA TRITICINA ON WHEAT IN THE UNITED STATES IN 2001. PLANT DISEASE. 2003. v. 87. p. 859-866. Interpretive Summary: Collections of the rust fungus Puccinia triticina, the cause of the leaf rust disease on wheat, were obtained from the major wheat growing regions of the U.S. in 2001. The collections of the leaf rust fungus were purified on seedlings of wheat plants in greenhouses and were then tested for their ability to attack 16 different types of wheat, that each have a different gene that gives resistance to the leaf rust fungus. From the many collections (477) that were tested on the wheat lines, 44 different types of leaf rust (physiologic races) were described in the U.S. in 2001. Races with the ability to attack leaf rust resistance genes Lr35 and Lr37 were detected for the first time in the U.S. Different races of leaf rust were found in the southeastern states and the Ohio Valley areas where soft red winter wheats are grown, compared with races that were found in the southern and northern Great Plains region of the U.S. where hard red winter and spring wheats, respectively, are grown. The leaf rust races differ in their ability to attack the different types of wheat cultivars that are grown in the U.S., which has led to the different wheat growing areas of the U.S. having different leaf rust races. The results from this study can be used by wheat breeders and plant pathologists to determine which leaf rust resistance genes can be added to wheat breeding programs in order to develop wheat cultivars with good resistance to the many different races of the leaf rust fungus.
Technical Abstract: Collections of Puccinia triticina were obtained from rust infected wheat leaves by cooperators throughout the United States and from surveys of wheat fields and nurseries in the Great Plains, Ohio Valley, Gulf Coast, California, Pacific Northwest, and Atlantic Coast States in order to determine the virulence of the wheat leaf rust fungus in 2001. Single uredinial isolates (477 in total) were derived from the wheat leaf rust collections and tested for virulence phenotype on lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes Lr1, Lr2a, Lr2c, Lr3, Lr9, Lr16, Lr24, Lr26, Lr3ka, Lr11, Lr17, Lr30, LrB, Lr10, Lr14a, and Lr18. The isolates were also tested for virulence on adult plants with leaf rust resistance genes Lr12, Lr13, Lr22a, Lr22b, Lr34, Lr35, and Lr37. In the United States in 2001, 44 virulence phenotypes of P. triticina were found. Virulence phenotype MBDS, which is virulent to resistance gene Lr17, was the most common phenotype in the United States. MBDS was found in the southeast, Great Plains, and the Ohio Valley regions. Virulence phenotype THBJ, which is virulent to Lr16 and Lr26, was the second most common phenotype and occurred almost exclusively in the north central Great Plains region. Phenotype MCDS, which is virulent to Lr17 and Lr26, was the third most common phenotype and was found primarily in the Southeast, Ohio Valley, and Great Plains regions. The southeast and Ohio Valley regions differed from the Great Plains regions for predominant virulence phenotypes, which indicate that populations of P. triticina in those areas are not closely connected. The northern and southern areas of the Great Plains region differed for phenotypes with virulence to Lr16, however the two areas had other phenotypes in common. Virulence to the adult plant resistance genes Lr35 and Lr37 was detected for the first time in North America primarily in the MBDS and MCDS phenotypes.