Virulence of Puccinia triticina, the wheat leaf rust fungus, in the United States in 2017

Authors: Kolmer, James

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2019
Publication Date: 6/3/2019
Citation: Kolmer, J.A. 2019. Virulence of Puccinia triticina, the wheat leaf rust fungus, in the United States in 2017. Plant Disease. https://doi.org/10.1094/PDIS-09-18-1638-SR.
DOI: https://doi.org/10.1094/PDIS-09-18-1638-SR

Interpretive Summary: Wheat is attacked by the rust fungus called Puccinia triticina, which causes the disease wheat leaf rust. There are many different forms or races of the wheat leaf rust fungus that vary in their ability to attack different resistance genes in wheat. Every year the USDA-ARS Cereal Disease Laboratory makes collections of the wheat leaf rust fungus from the major wheat growing regions of the United States to determine which forms of P. triticina are present. In 2017, 65 different forms of the leaf rust fungus were found in the United States. The forms with virulence to the resistance genes in the commonly grown hard red winter wheats were widespread throughout the eastern states and the Great Plains region. The races with virulence to the genes present in the soft red winter wheats were found in the eastern states and the Ohio Valley region. The most commonly grown hard red winter wheat cultivars and soft red winter wheat cultivars are susceptible to the most common leaf rust races found in the regions where these wheat cultivars are grown. It will be important to develop wheat cultivars with new combinations of leaf rust resistance genes in the winter wheat regions. The results from the annual virulence survey are used by wheat breeders and plant pathologists to help develop wheat cultivars that are very resistant to the leaf rust disease.

Technical Abstract: Samples of wheat leaves infected with the leaf rust fungus, Puccinia triticina, were obtained from agricultural experiment station plots, demonstration plots, and farm fields in the Great Plains, the Ohio Valley, the southeastern states in 2017, California and Washington in order to determine the prevalent virulence phenotypes present in the United States in 2017. A total of 71 virulence phenotypes were identified among the 469 single uredinial isolates that were tested on 20 near isogenic lines of Thatcher wheat that differ for leaf rust resistance genes. Virulence phenotypes MBTNB at 11.3% of the overall population, and MCTNB at 7.0%, were the first and third most common phenotypes. Both phenotypes were found mostly in the southeastern states and Ohio Valley region. Phenotype TFTSB at 10.9%, was the second most common phenotype and was found mostly in southern Texas. Virulence to leaf rust resistance gene Lr39 which is present in hard red winter wheats, was highest in the Great Plains region. Virulence to Lr11 and Lr18, which are present in soft red winter wheat cultivars, was highest in the southeastern states and Ohio Valley region. Virulence to Lr21, which is present in hard red spring wheat cultivars, was highest in the northern Great Plains region. The P. triticina collections from the soft red winter wheat region of the southeastern states and Ohio Valley area differed for virulence phenotypes compared to the population from the hard red winter and hard red spring wheat areas of the Great Plains region. Collections from Washington state had unique virulence phenotypes that had not previously detected.