Virulence phenotypes of the wheat leaf rust pathogen, Puccinia triticina, in the United States 2018-2020

Authors: Kolmer, James; Fajolu, Oluseyi

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2021
Publication Date: 1/3/2022
Citation: Kolmer, J.A., Fajolu, O.L. 2022. Virulence phenotypes of the wheat leaf rust pathogen, Puccinia triticina, in the United States 2018-2020. Plant Disease. 106(6):1723-1729. https://doi.org/10.1094/pdis-10-21-2321-re.
DOI: https://doi.org/10.1094/pdis-10-21-2321-re

Interpretive Summary: Wheat is attacked by the leaf rust fungus called Puccinia triticina. Leaf rust causes yield losses on a yearly basis in the U.S. Many different biotypes or races of P. triticina are found in the U.S. and worldwide. When wheat cultivars with leaf rust resistance genes are grown, the leaf rust race population can adapt quickly as races that can attack the resistance genes increase very rapidly. New races that can attack wheat cultivars are constantly appearing in the wheat growing regions of the U.S. The objectives of this study were to summarize results from 2018, 2019, and 2020 of the yearly race survey in the U.S. that is conducted by the USDA-ARS Cereal Disease Laboratory. Collections of P. triticina from the U.S. in these three years were processed for race identification in greenhouse tests. In the northern Great Plains of Minnesota, South Dakota, and North Dakota, races MNPSD, MPPSD, MBDSD, and TBBGS were the most common races. These races can attack wheat cultivars that are grown in this region that have genes Lr17, Lr37, Lr24, and Lr21. Races MBTNB, MCTNB were the most common races in the southeastern states and Ohio Valley states, and can attack the wheat cultivars that have gene Lr11. Different races of P. triticina have been found for many years in the southeastern states, Ohio Valley compared to races in the Great Plains region. These regions differ for characteristic leaf rust races since different types of wheat cultivars that differ for leaf rust resistance genes are grown in these regions. The results from this study can be used to develop new cultivars of wheat that have combinations of leaf rust resistance genes that give good resistance to all current races in the U.S.

Technical Abstract: Collections of wheat leaves infected with the leaf rust fungus, Puccinia triticina, were obtained from the southeastern states, the Ohio Valley, the Great Plains, and Washington in 2018, 2019 and 2020 in to determine the prevalent virulence phenotypes in the wheat growing regions of the United States. In the hard red winter wheat region of the southern and mid Great Plains, MNPSD, and MPPSD were the two most common phenotypes in 2018 and 2019. In 2020 BBBQB with high virulence to durum wheat was the most common phenotype in the southern Great Plains. In the hard red spring wheat region of the northern Great Plains, MNPSD, MPPSD, MBDSD, and TBBGS were the predominant phenotypes. In the soft red winter wheat region of the southeastern states and Ohio Valley region, MBTNB, MCTNB, and MNPSD were the three most common phenotypes. Collections in Washington had phenotypes LBDSG, LCDSG, LCDJG, and MBDSB that were not found in any other region. Isolates with virulence to Lr11 were highest in the southeastern states, and Ohio Valley regions. The frequency of isolates with virulence to Lr39 were highest in the Great Plains region and isolates with virulence to Lr21 were highest in the northern Great Plains region. Selection of virulence phenotypes by leaf rust resistance genes in the different market classes of wheat has maintained the different P. triticina populations in the United States.