Pathovar identification and genetic diversity of Xanthomonas translucens strains isolated from weedy grasses and cultivated wild rice in Minnesota

Abstract

Bacterial leaf streak (BLS) of wheat, caused by Xanthomonas translucens pv. undulosa, has been prevalent in Minnesota wheat fields for the past decade. Infested seed and crop debris can serve as inoculum for subsequent crops. Weeds are also considered a potential inoculum source, but little is known about specific pathovars and genetic diversity among strains of X. translucens from these different hosts. The objectives of this study were to isolate X. translucens from poaceous weeds and cultivated wild rice in Minnesota, determine pathogenicity of these strains on wheat and barley, assess phylogenetic relationships and genetic diversity of strains using multilocus sequence analysis (MLSA) and typing (MLST) of four housekeeping genes (rpoD, dnaK, fyuA, and gyrB), and evaluate the efficacy of loop-mediated isothermal amplification (LAMP) assays designed to identify X. translucens pathovars that cause BLS on small grains. Bacteria were isolated from 157 plant samples, representing 12 poaceous hosts collected in and around commercial fields of wheat and wild rice. Strains exhibiting characteristic colony morphology on Wilbrink’s medium were purified and evaluated further. The majority (87/134) of Xanthomonas strains were predicted to be X. translucens by 16S rDNA sequencing. A subset (51) of the strains predicted to be X. translucens were infiltrated into leaves of wheat and barley seedlings and found to cause disease. Eight of these strains were also tested in the field and likewise caused disease on wheat and barley. Phylogenies from MLSA show that strains from weedy grasses and wild rice are closely related to known X. translucens pathovars, most commonly X. translucens pv. undulosa. The findings suggest that poaceous weeds and cultivated wild rice have potential to serve as reservoirs of inoculum for the bacterial pathogen inciting BLS of wheat.