Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2002
Publication Date: 9/1/2002
Citation: LONG, D.L., KOLMER, J.A., LEONARD, K.J., HUGHES, M.E. PHYSIOLOGIC SPECIALIZATION OF PUCCINIA TRITICINA ON WHEAT IN THE UNITED STATES IN 2000. PLANT DISEASE. 2002. v. 86. p. 981-986. Interpretive Summary: Collections of the rust fungus Puccinia triticina, which is the cause of the leaf rust disease on wheat, were obtained from the major wheat-growing regions of the U.S. in 2000. The collections of the leaf rust fungus were purified on seedlings of wheat plants in greenhouses and then tested for their ability to attack 16 different types of wheat. Each type of wheat has a different gene that gives resistance to the leaf rust fungus. From the many collections (1,120) that were tested on the wheat lines, 54 different types of leaf rust (physiologic races) were described in the U.S. in 2000. 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 lead 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, and Atlantic Coast States, in 2000. Single uredinial isolates (1120 in total) were derived from the wheat leaf rust collections and tested for virulence phenotype on 16 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes. In the United States in 2000, 54 virulence phenotypes of P. triticina were found. Virulence phenotypes MBDS and MCDS, which are virulent to resistance gene Lr17, were the first and third most common phenotypes in the United States. MBDS and MCDS were found in the Great Plains and the Ohio Valley regions. MCRK, which is virulent to Lr26, was the second most common phenotype and was found primarily in the southeast, Ohio Valley, and northeast regions. In the northern area of the Great Plains, phenotypes with virulence to Lr16 increased in frequency compared to previous years. The southeast and Great Plains regions differed 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 had the same predominant virulence phenotypes, indicating movement of P. triticina virulence phenotypes within this region.