Identification of New Sources of Resistance in Winter Wheat to Multiple Strains of Xanthomonas translucens pv. undulosa.

Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa, has re-emerged as an important disease of wheat (Triticum aestivum) in the United States. Planting resistant varieties is the best approach to manage BLS in the absence of effective bactericides. However, most of the wheat varieties currently grown in the Upper Midwest of the United States appeared to be susceptible to BLS. From the core subset of the USDA National Small Grain Collection (NSGC), a set of 605 winter wheat accessions of diverse origin and improvement status were initially inoculated with a virulent strain BLSW16 of X. translucens pv. undulosa from Casselton, ND on the flag leaf of each plant in a greenhouse. Disease reactions were assessed between 7 and 10 days after infiltration using a 0 to 6 rating scale, where ≤2.0 was considered resistant and >2.1 was considered susceptible. Resistance varied with geographic origin and was significantly (P ≤ 0.05) more frequent in accessions from North America compared to accessions from northern, eastern, and southern Europe and from south-central Asia. About 8.3% of accessions tested were resistant, and accessions with an improvement status of "cultivar" were significantly more likely to be resistant than were accessions classified as either landraces or breeding lines. Forty-two of the accessions exhibiting resistance in response to the strain BLSW16 in the first screening test were retested utilizing each of the two additional strains (BLS Cr25 and BLS Lb74 of X. translucens pv. undulosa) collected from Carrington and Lisbon, respectively. Nonparametric data analysis revealed 35 accessions were resistant, one accession, PI 266860, was susceptible to both strains, and six accessions showed differential responses. The majority of the BLS-resistant accessions also were resistant to at least one other important wheat disease based on the Germplasm Resources Information Network (GRIN) data. These results suggest that diverse and novel sources of resistance to BLS identified in this study can be utilized in winter wheat breeding programs.