Bacterial leaf streak (BLS) of wheat and barley, caused by Xanthomonas translucens pv. undulosa and X. translucens pv. translucens, has been of growing concern in small grains production in the Upper Midwestern United States. To optimize disease resistance breeding, a greater awareness is needed of the pathovars and genetic diversity within the pathogens causing BLS in the region. Multilocus sequencing typing (MLST) and analysis (MLSA) of four common housekeeping genes (rpoD, dnaK, fyuA, and gyrB) was used to evaluate the genetic diversity of 82 strains of X. translucens isolated between 2006 and 2013 from wheat, barley, rye, and intermediate wheatgrass. In addition, in planta disease assays were conducted on 75 strains to measure relative virulence in wheat and barley. All strains were determined by MLSA to be related to X. translucens pv. undulosa and X. translucens pv. translucens. Clustering of strains based on Bayesian, network, and minimum spanning trees correlated with relative virulence levels in inoculated wheat and barley. Thus, phylogeny based on rpoD, dnaK, fyuA, and gyrB correlated with host of isolation and was an effective means for predicting virulence of strains belonging to X. translucens pv. translucens and X. translucens pv. undulosa.

An outbreak of bacterial soft rot and blackleg of potato has occurred since 2014 with the epicenter being in the northeastern region of the United States. Multiple species of Pectobacterium and Dickeya are causal agents, resulting in losses to commercial and seed potato production over the past decade in the Northeastern and North Central United States. To clarify the pathogen present at the outset of the epidemic in 2015 and 2016, a phylogenetic study was made of 121 pectolytic soft rot bacteria isolated from symptomatic potato; also included were 27 type strains of Dickeya and Pectobacterium species, and 47 historic reference strains. Phylogenetic trees constructed based on multilocus sequence alignments of concatenated dnaJ, dnaX and gyrB fragments revealed the epidemic isolates to cluster with type strains of D. chrysanthemi, D. dianthicola, D. dadantii, P. atrosepticum, P. brasiliense, P. carotovorum, P. parmentieri, P. polaris, P. punjabense, and P. versatile. Genetic diversity within D. dianthicola strains was low, with one sequence type (ST1) identified in 17 of 19 strains. Pectobacterium parmentieri was more diverse, with ten sequence types detected among 37 of the 2015–2016 strains. This study can aid in monitoring future shifts in potato soft rot pathogens within the U.S. and inform strategies for disease management.

Intermediate wheatgrass (IWG, Thinopyrum intermedium, (Host) Barkworth & D.R. Dewey subsp. intermedium, 2n = 6x = 42) is a novel perennial crop currently undergoing domestication efforts. It offers remarkable ecosystem services and yields higher relative to other perennial grain crops. While IWG is mostly resistant to Fusarium head blight (FHB), identifying genomic regions associated with resistance will help protect the crop from potential disease epidemics. An IWG biparental population of 108 individuals was developed by crossing parents differing in their response to FHB and bacterial leaf streak (BLS). The population was screened for disease reaction over three years using isolates collected from IWG plants in St. Paul, Minnesota, USA. Linkage maps representing the 21 IWG chromosomes were constructed from 4622 Single Nucleotide Polymorphism (SNP) markers, with one SNP at every 0.74 cM. Interval mapping identified 15 quantitative trait loci (QTL) associated with FHB resistance and 11 with BLS resistance. Models with two or three QTL combinations reduced FHB disease severity by up to 15%, and BLS by up to 17%. When markers associated with FHB resistance were used as cofactors in genomic selection models, trait predictive ability improved by 24-125%. These genomic regions and genetic markers associated with FHB and BLS resistance can also be used to safeguard annual cereal grains through gene introgression and selective breeding.