Barley field, St. Paul campus.

2022-23 Rapid Ag: Genetics and Breeding of Bacterial Leaf Streak Resistance in Barley (Renewal)

February 26, 2021

Project Leader

Brian Steffenson, Department of Plant Pathology

Team Members and Roles

  • Ruth Dill-Macky, Department of Plant Pathology
  • Rebecca Curland, Department of Plant Pathology
  • Kevin Smith, Department of Agronomy & Plant Genetics
  • Jochum Wiersma, Small Grains Extension, Department of Agronomy & Plant Genetics 

Non-Technical Summary

Bacterial Leaf Streak (BLS), caused by Xanthomonas translucens pv. translucens, has emerged as a widespread and serious disease of barley in Minnesota. Deployment of resistant cultivars is the most effective strategy for managing the disease since fungicides have little efficacy against the causal bacterium. From our 2020-2021 RARF research, we identified highly resistant accessions from diverse barley germplasm panels in field trials conducted in 2020. To efficiently utilize these sources in breeding, it is essential to characterize the genetic architecture of resistance. Thus, the objectives of this investigation are to: 1) develop populations from these sources to characterize the number, chromosomal location, and effect of loci conferring BLS resistance; 2) select agronomically advanced, BLS resistant progeny from these populations that can feed directly into the breeding pipeline; and 3) educate producers and agricultural professionals on options for managing the disease. The key outcomes from this research will be the development of malting barley varieties with BLS resistance which, in turn, will allow more profitable and sustainable production of this important agricultural commodity to Minnesota.

Objectives and Goals

The overall goals of this project are to characterize the genetic architecture of BLS resistance in five diverse barley accessions and develop, as quickly as possible, barley varieties that are resistant to BLS, thereby ameliorating the losses due to this important disease. The specific objectives of the project are to:

  1. Develop populations from five diverse resistance sources to characterize the number, chromosomal location, and effect of loci conferring BLS resistance;
  2. Select agronomically advanced, BLS resistant progeny from these populations that can feed directly into the breeding pipeline
  3. Educate producers and agricultural professionals on options for managing the disease.

Justification

BLS has emerged as a perennial disease problem of barley and wheat throughout the Upper Midwest production area. The disease is caused by the bacterium Xanthomonas translucens with X. translucens pv. translucens considered the primary pathovar adapted to barley and X. translucens pv. undulosa considered the primary pathovar adapted to wheat (Bragard et al. 1995; Vauterin et al. 1995). A recent study has shown that both pathovars are present in the Upper Midwest with X. translucens pv. translucens identified as the causal agent of BLS of barley in Minnesota (Curland et al. 2018). Furthermore, Minnesota isolates of X. translucens pv. translucens associated with BLS on barley are genetically diverse as three distinct phylogenetic clades have been detected from molecular assays of populations (Curland et al. 2018, 2020). For these reasons, BLS research must be conducted on a specific pathovar and crop basis with consideration of the diversity of regional pathogen populations. Disease surveys of commercial barley crops conducted over the past 18 years have revealed a general increase in the incidence and severity of BLS in Minnesota. For example, in 2005, 2009, 2011, and 2013, 80-100% of surveyed fields were infected with severities in individual fields reaching up to 70% (B. Steffenson, unpublished). Field studies of BLS impact on barley revealed yield losses ranging from 13 to 20% (R. Dill-Macky, unpublished; Shane et al. 1987). The potential for this bacterial disease to affect malting and brewing quality is also possible since the pathogen can be seed-borne (Duveiller et al. 1997; Paulitz and Steffenson 2011). The reasons for the increased incidence and severity of the disease in the region are not well understood. It is possible that the pathogen has become better adapted to the region (perhaps due to increasing temperatures and wet weather), current varieties, and/or alternative grass hosts, which can serve as a source of pathogen inoculum (Ledman et al. 2020). Additionally, changes in cropping practices may have facilitated greater survival of the pathogen in crop debris. Since the bacterium can be seed-borne, it is likely that spread of the disease occurred when growers used infected seed for sowing their crop. Regardless of the reasons, the increasing use of fungicides on barley likely led to an increased awareness of the problem since BLS symptoms are easier to discern when fungal infections are absent.

The short-term strategy of educating producers and agricultural professionals about BLS can pay immediate dividends for reducing the impact of the disease. First, since X. translucens pv. translucens is known to be seed-borne, it is important for producers to avoid using seed from a heavily infected crop for next spring’s sowing. Second, the BLS pathogen can overwinter in infected crop debris; thus, it is critical for producers to practice proper crop rotation to reduce the disease. The contributions of these two inoculum sources is being investigated in a separate funded project through the Small Grains Initiative. Third, since the current barley varieties vary markedly in their reaction to BLS, it is important to avoid planting the most susceptible ones (Smith et al. 2018). In this regard, we will rigorously evaluate common barley varieties and recently identified resistant accessions to a suite of different X. translucens pv. translucens isolates from the three main phylogenetic clades of the pathogen found in Minnesota and report the results to producers and agricultural professionals at various outreach events (field days, commodity meetings) as well as in the Minnesota Field Crop Trials bulletin. Fourth, it is critical for producers to understand that commonly used fungicides do not control BLS because it is caused by a bacterium. In the long-term, resistant varieties are the most effective and environmentally benign means of controlling BLS. Although it may take about seven years to develop a resistant variety, this time period can be reduced by about two years because we have identified native BLS resistance in agronomically advanced breeding lines from two premiere Midwest-based malting barley breeding programs, both of which routinely employ genomic selection to speed the selection process.

References

  • Bragard, C., Verdier, V., and Maraite, H. 1995. Genetic diversity among Xanthomonas campestris strains pathogenic for small grains. Appl. Environ. Microbiol. 61:1020-1026.
  • Curland, R., et al. 2018. Genetic diversity and virulence of wheat and barley strains of Xanthomonas translucens from the Upper Midwestern United States. Phytopathology 108:443-453.
  • Curland, R., Gao, L., Hirsch, C., and Ishimaru, C. 2020. Localized genetic and phenotypic diversity of Xanthomonas translucens associated with bacterial leaf streak on wheat and barley in Minnesota. Phytopathology 110:257–266.
  • Duveiller, E., Fucikovsky, L., and Rudolph, K. 1997. The Bacterial Diseases of Wheat: Concepts and Methods of Disease Management. CIMMYT Mexico, D.F.
  • Ledman, K. E., Curland R. D., Ishimaru C. A., and Dill-Macky, R. 2020. Weedy grasses as a potential reservoir of the pathogen causing bacterial leaf streak of wheat. Phytopathology (abstract) in press.
  • Mascher, M., G. J. Muehlbauer, D. S. Rokhsar, J. Chapman, J. Schmutz et al., 2013. Anchoring and ordering NGS contig assemblies by population sequencing (POPSEQ). Plant J. 76: 718–727.
  • Mascher, M., H. Gundlach, A. Himmelbach, S. Beier, S. O. Twardziok et al., 2017. A chromosome conformation capture ordered sequence of the barley genome. Nature 544: 427–433.
  • Nice, L. M., et al. 2016. Development and genetic characterization of an advanced backcross-nested association mapping (AB-NAM) population of wild × cultivated barley. Genetics 203:1453-1467.
  • Paulitz, T., and Steffenson B.J. 2011. Biotic stresses in barley: problems and solutions. Pages 307-354 in: Ullrich, S.E. (ed.) Barley: Production, Improvement and Uses.
  • Wiley-Blackwell, Ames, IA. Shane, W. W., Baumer, J. S., and Teng, P. S. 1987. Crop losses caused by Xanthomonas streak on spring wheat and barley. Plant Dis. 71:927-930.
  • Smith, K. P., et al. 2010. Registration of ‘Rasmusson’ Barley. J. Plant Registr. 4: 167-170.
  • Smith, K., et al. 2018. Preliminary Report 24: 2018 Barley Variety Performance in Minnesota. Minnesota Agricultural Experiment Station, University of Minnesota Extension, St. Paul, MN.
  • Vauterin, L., Hoste, B., Kersters, K., and Swings, J. 1995. Reclassification of Xanthomonas. Int. J. Syst. Evol. Microbiol. 45:472-489.