Location: Cereal Disease LabTitle: First Report of a wheat leaf rust (Puccinia triticina) phenotype with high virulence to durum wheat in the Great Plains region of the U.S.
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2014
Publication Date: 1/1/2015
Citation: Kolmer, J.A. 2015. First Report of a wheat leaf rust (Puccinia triticina) phenotype with high virulence to durum wheat in the Great Plains region of the United States. Plant Disease. 99:56.
Interpretive Summary: A race of the wheat leaf rust fungus, Puccinia triticina, with virulence to durum wheat cultivars that are grown in the U.S. was detected for the first time in 2013 in the Great Plains region in Kansas. This race of leaf rust is also virulent to many of the most commonly grown winter wheat cultivars in the southern Great Plains. Races of leaf rust with high virulence to durum wheat may become established on the winter wheats and spread to the durum wheat growing region in North Dakota. If races with virulence to durum wheat become established in the Great Plains, losse due to leaf rust would be expected since all of the currently grown U.S. durum wheat cultivars are susceptible.
Technical Abstract: Phenotypes of the wheat leaf rust pathogen Puccinia triticina with high virulence to tetraploid durum wheat (Triticum turgidum) are found regularly in Mexico, the Mediterranean region, the Middle East, and rarely in the Imperial Valley in California, and the adjacent area in Arizona. Previous to 2013 these phenotypes had not been found in the Great Plains region of the U.S. where hexaploid, T. aestivum types of hard red winter wheat, hard red spring wheat, and durum wheat are grown. In May 2013, collections of Puccinia triticina, the wheat leaf rust fungus, were obtained from the hard red winter wheat cultivar 'Overley' in research plots at Hutchinson Kansas. Single uredinia from the collection were isolated and increased on the susceptible wheat cultivar 'Little Club'. The single uredinial isolates were initially inoculated to 7 day old seedlings of 20 lines of 'Thatcher' wheat that are near-isogenic for leaf rust resistance genes and are used in the annual virulence surveys of P. triticina in the U.S. The phenotype of the isolate based on virulence to the 20 differential lines was BBBQD, which was identical to phenotypes of P. triticina with high virulence to durum wheat from other regions where durum wheat is commonly grown. This phenotype had intermediate infection type of 2+ (moderate size uredinia with chlorosis) to the line with Lr2c, and high infection types of 3+ (large uredinia with no chlorosis or necrosis) to lines with genes LrB, Lr10, and Lr39/41 that is also present in Overley wheat. The isolates were further tested on an additional set of 27 Thatcher lines, the cultivar 'Gatcher' with Lr27 + Lr31, and a set of 15 durum wheat cultivars that have been grown in the U.S. and Canada. The isolates had virulence to lines with genes Lr14b, Lr20, Lr23, Lr33, Lr44, and Lr64. Notably the isolates had distinct low infection types to seedlings of Thatcher lines with genes Lr12, Lr13, Lr22a, Lr35 and Lr37 that are usually optimally expressed in adult plants to most P. triticina isolates. The isolates had high virulence to all of the durum wheat cultivars. The phenotype with high virulence to durum wheat most likely migrated to the southern Great Plains region from the durum growing regions in Mexico. In addition to Overley, hard red winter wheat cultivars such as 'TAM 112', 'Armour', 'Winterhawk', and 'Bullet' with Lr39/41 are currently grown throughout the southern Great Plains. Since many of the P. triticina phenotypes with high virulence to durum wheat are virulent to Lr39/41, these cultivars may provide a pathway for the spread of these phenotypes to the major durum producing areas of North Dakota and Saskatchewan.