Evaluating Copper Resistance in Xanthomonas translucens Strains Associated with Bacterial Leaf Streak of Wheat and Barley in Minnesota
Bacterial leaf streak (BLS) is a disease of cereal grains, with Xanthomonas translucens pv. translucens affecting wheat and X. translucens pv. undulosa affecting barley. BLS is a persistent problem in the Upper Midwest with no available chemical control. This project tested a collection of 230 strains (81 X. translucens pv. translucens and 149 X. translucens pv. undulosa) from recent outbreaks of BLS in the Upper Midwest on GNA (glucose nutrient agar) media amended with 150 ug/mL copper sulfate to screen for copper resistance in those strains. Five of the 81 X. translucens pv. translucens strains (6.2%) exhibited growth on copper amended media, whereas two of the 149 X. translucens pv. undulosa strains (1.3%) exhibited growth on GNA + 150 ug/mL. The seven strains with suspected copper resistance were plated multiple times, with growth on copper amended media only being present some of the time and with varying degrees of growth on GNA + copper sulfate, suggesting variable tolerance to copper sulfate. Subsequently, the seven copper tolerant strains were grown on a range of copper sulfate concentrations, along with a negative control. The selected strains were able to grow at concentrations above 100 ug/mL, whereas the negative control showed copper tolerance at concentrations up to 100 ug/mL. The strains identified in this study could be further tested in field or greenhouse studies to determine tolerance to commercially available copper compounds. Additionally, genomic analyses could be performed to determine potential loci that contribute to copper tolerance and resistance.