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Weedy grasses as a potential reservoir of the pathogen causing bacterial leaf streak of wheat

Kristi Ledman: University of Minnesota

<div>Bacterial leaf streak (BLS) of wheat, caused by <em>Xanthomonas translucens</em> pv. <em>undulosa</em>, has been prevalent in Minnesota wheat fields for the past decade. Sources of the pathogen include infested seed and crop debris. Weeds are also considered a potential inoculum source, but little is known about the genetic similarities among isolates of <em>X. translucens </em>from these different hosts. The objectives of this study were to isolate <em>X. translucens</em> from poaceous weeds in Minnesota, determine pathogenicity of weed isolates on wheat and barley, and to evaluate phylogenetic relationships of isolates from weeds and those from small grains. Bacteria were isolated from 130 samples representing 12 grass species collected in and around wheat fields. Isolates exhibiting characteristic colony morphology on Wilbrink’s medium were purified and evaluated further. The majority (68/98) of the isolates were identified as <em>X. translucens</em> by 16S rDNA sequencing. A subset (47) of these isolates were infiltrated into leaves of wheat and barley seedlings and found to cause disease. Phylogenies of the weed isolates were constructed using sequence alignments of four housekeeping genes (<em>rpoD, dnaK, fyuA </em>and <em>gyrB</em>). Phylogenies from multilocus sequence analysis show that these isolates are closely related to known <em>X. translucens </em>pathovars, most commonly <em>X. translucens</em> pv. <em>undulosa. </em>Our findings suggest that poaceous weeds serve as a reservoir of inoculum for the bacterial pathogen inciting BLS of wheat.</div>