P-563 - Genomics and Mating Type Genes involved in Wheat and Rye Stem Rust Admixture Events

Monday, August 4, 2025

4:30 PM - 5:15 PM HST

Location: Exhibit Hall 3

Presenting Author(s)

TI

Thomas W. Ingram (he/him/his)

Postdoc
University of Minnesota
St Paul, Minnesota, United States

Author(s)

MV

Molly Veregge

Graduate Student
University of Minnesota
St Paul, Minnesota, United States
YJ

Yue Jin

USDA ARS Cereal Disease Laboratory
St Paul, Minnesota, United States
Ea

Eduard akhunov

Kansas State University
Manhattan, Kansas, United States
PO

Pablo Olivero-Firpo

Research Plant Pathologist
USDA ARS Cereal Disease Laboratory
St Paul, Minnesota, United States
MM

Matthew Moscou

Research Plant Pathologist
USDA ARS Cereal Disease Laboratory
St Paul, Minnesota, United States
MR

Matthew Rouse

USDA ARS Sugarcane Field Station
Canal Point, Florida, United States

Abstract Text: Puccinia graminis is the causal agent of wheat (f. sp. tritici, Pgt) and rye (f. sp. secalis, Pgs) stem rust. While they are the same species, host specificity is high. Pgt and Pgs are rarely able to infect their counterparts' hosts. Importantly ~25% of deployed stem rust resistance genes (Sr) in wheat are derived from rye introgressions. The goal of this study is to understand the scale of wheat and rye stem rust admixture events. An analysis of whole genome data from 380 Pg isolates has revealed that in North America (NA) Pgs and Pgt have undergone recombination in the near distant past, and are still recombining. Many of these hybrids were isolated from barley or barberry, common hosts for Pgs and Pgt. In addition to a phylogenetic analysis, over 100 haplotypes of the mating type homeodomain locus (HD) were discovered. The HD haplotype Pg-bWbE096 was present in many Pgt and Pgs isolates, indicating a recent admixture event. Most HD haplotypes are only 60-80% similar in pairwise comparisons, showing a high level of diversifying selection. The NA population had the highest number of Pgt/Pgs hybrids, and 18 HD haplotypes (n=151), compared to Asia which had 50 haplotypes (n=101). This difference in diversity indicates that Pg has been evolving in Asia for much longer than it has in NA. Successful Pgt races, such as race QFCSC, group with the hybrids, demonstrating hybridization may also improve long term fitness. Important Sr genes such as Sr31 have been overcome by Pgs in NA, monitoring these admixture events is crucial to maintaining wheat production in NA and globally.