Localized Genetic and Phenotypic Diversity of Xanthomonas translucens Associated With Bacterial Leaf Streak on Wheat and Barley in Minnesota.

Bacterial leaf streak (BLS) of wheat and barley has been a disease of increasing concern in the Upper Midwest over the past decade. In this study, intra- and interfield genetic and pathogenic diversity of bacteria causing BLS in Minnesota was evaluated. In 2015, 89 strains were isolated from 100 leaf samples collected from two wheat and two barley fields naturally infected with BLS. Virulence assays and multilocus sequence alignments of four housekeeping genes supported pathovar identifications. All wheat strains were pathogenic on wheat and barley and belonged to the same lineage as the Xanthomonas translucens pv. undulosa-type strain. All barley strains were pathogenic on barley but not on wheat. Three lineages of barley strains were detected. The frequency and number of sequence types of each pathovar varied within and between fields. A significant population variance was detected between populations of X. translucens pv. undulosa collected from different wheat fields. Population stratification of X. translucens pv. translucens was not detected. Significant differences in virulence were detected among three dominant sequence types of X. translucens pv. undulosa but not those of X. translucens pv. translucens. Field trials with wheat and barley plants inoculated with strains of known sequence type and virulence did not detect significant race structures within either pathovar. Knowledge of virulence, sequence types, and population structures of X. translucens on wheat and barley can support studies on plant-bacterial interactions and breeding for BLS disease resistance.