|Bonman, John - Mike|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2011
Publication Date: 4/1/2012
Citation: Adhikari, T.B., Gurung, S., Hansen, J.M., Bonman, J.M. 2012. Pathogenic and genetic diversity of Xanthomonas translucens pv. undulosa populations in North Dakota. Phytopathology. Vol. 102, No. 4, 2012. Interpretive Summary: The bacterium Xanthomonas translucens pv. undulosa causes a disease called bacterial leaf streak (BLS) in wheat. The disease is becoming more serious in the US, particularly in the upper Midwest. A first step in managing this disease is to better understand the genetic and pathogenic variability of the pathogen. Such knowledge will aide in breeding resistant wheat cultivars, which is one of the primary means of managing BLS. Using inoculation tests and molecular markers, we discovered that the BLS pathogen is highly variable in North Dakota. Future work should seek to identify wheat germplasm resistant to multiple strains of this pathogen.
Technical Abstract: Xanthomonas translucens pv. undulosa causes bacterial leaf streak (BLS) disease in wheat (Triticum aestivum L.). In recent years, severe BLS outbreaks have been reported in the Upper Midwest of the United States, particularly in North Dakota and adjacent wheat growing states. To assess pathogenic and genetic variation within the pathogen population in North Dakota, 226 strains of X. translucens were collected from five populations within the state and first tested for pathogenicity on wheat and barley cultivars. The 16S ribosomal RNA (rRNA) region of randomly selected strains of X. translucens pv. undulosa was sequenced and compared with reference strains and other pathovars of Xanthomonas. In further pathogenicity tests, representative strains from the five populations were infiltrated on 12 wheat cultivars and different cereal host plants. All strains were identified as X. t. pv. undulosa and 29 pathotypes were detected. Each strain was unique pathotype and was more virulent on wheat and barley than other cereal hosts tested. The genetic diversity of five populations of X. t. pv. undulosa in North Dakota was analyzed using repetitive sequence-based polymerase chain reaction (rep-PCR) and insertion sequence-based PCR (IS-PCR) primers. In all, 213 distinct haplotypes were detected and almost all were unique across five populations. Population genetic analysis revealed moderate level of gene diversity (H = 0.19 to 0.24) and significant (P = 0.001) gametic disequilibrium (r ¯d). Furthermore, the corrected standardized fixation index (G’’ST) values ranged from 0.011 to 0.218 between populations and the pair-wise comparisons between the majority of populations were statistically significant (P = 0.001 and P = 0.05), indicating differentiation of X. t. pv. undulosa populations in North Dakota. Analysis of molecular variance (AMOVA) also indicated a small but statistically significant (0.001) genetic differentiation between populations. However, high genetic variation (~92%) occurred among individuals within populations while low genetic variation (~8%) was detected between populations. The results of this study suggest that these X. t. pv. undulosa strains in North Dakota are pathologically and genetically diverse and likely represent a heterogeneous population causing BLS epidemics in wheat and barley.