PHYSIOLOGIC SPECIALIZATION OF PUCCINIA TRITICINA ON WHEAT IN THE UNITED STATES IN 2002

Authors: Kolmer, James; Long, David; Hughes, Mark

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2004
Publication Date: 10/1/2004
Citation: Kolmer, J.A., Long, D.L., Hughes, M.E. 2004. Physiologic specialization of Puccinia triticina on wheat in the United States in 2002. Plant Disease. 88:1079-1084

Interpretive Summary: Collections of the rust fungus Puccinia triticina, that is the cause of the leaf rust disease on wheat, were obtained from the major wheat growing regions of the U.S. in 2002. 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 (785) that were tested on the wheat lines, 52 different types of leaf rust (physiologic races) were described in the U.S. in 2001. 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, Southeast, California, and the Pacific Northwest, in order to determine the virulence of the wheat leaf rust fungus in 2002. Single uredinial isolates (785 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. In the United States in 2002, 52 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, and also in California. Phenotype MCDS, virulent to Lr17 and Lr26, was the second most common phenotype and occurred in the same regions as MBDS. Virulence phenotype THBJ, which is virulent to Lr16 and Lr26, was the third most common phenotype, and was found in the southern and northern central Great Plains region. Phenotype TLGJ, with virulence to Lr2a, Lr9, and Lr11, was the fourth most common phenotype, and was found primarily in the Southeast and Ohio Valley 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 were similar for frequencies of predominant phenotypes, indicating a strong south to north migration of urediniospores.