Harrison, Steven , Boose, David , Clement, Suzette , Lee, Caitlin , Meyer, Susan E. .
Molecular genetic variation in Pyrenophora semeniperda as characterized by analysis of the internal transcribed spacer (ITS) region.
Pyrenophora semeniperda is a seed bank pathogen known to infect the seeds of Bromus tectorum (cheatgrass). Pathogen isolates were obtained by culturing fungal stromata from cheatgrass seeds found in field-collected seed bank samples. We were able to propagate 491 isolates from 20 populations in Utah, Arizona, Colorado, Idaho, and Washington. Alignment of the internal transcribed spacer (ITS) region produced a homologous region 486 nt in length with 13 nucleotide substitutions and 8 insertion/deletions. This variation produced 12 unique haplotypes. Each of the 20 populations contained at least two haplotypes and three populations had as many as six. Two haplotypes (A and H/I) were by far the most abundant, appearing at 100% and 90% of the sampled locations, and comprising 62% and 19.5% of the isolates, respectively. Analysis of Molecular Variance (AMOVA) revealed small but significant genetic differentiation among populations (10.2% of total variation; P=0.000), but most genetic variation (89.8%) was distributed within populations. When populations were subdivided between southern (UT, CO, and AZ) and northern (WA and ID) regions, AMOVA detected significant differentiation between the regions (P=0.00196), with 8.8% of the genetic variation due to differences between regions, 5.6% due to variation among populations within regions, and 85.6% due to variation within populations. When populations were grouped by habitat (mesic vs. xeric), no significant between-habitat variation was detected. Correlations between genetic and geographic distances were weak, indicating that some isolation by distance may be occurring, but that other processes are required to explain the observed distribution of genetic variation. The discovery that the pathogen can disperse by hitch-hiking on the seeds of its host, which are specifically adapted for long-distance dispersal, may help to explain patterns of genetic variation in this organism.
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1 - Brigham Young University, Plant and Wildlife Sciences, 287 Widtsoe Building, Provo, Utah, 84602 , United States
2 - Gonzaga University, Department of Biology, 502 East Boone Avenue, Spokane, Washington, 99258, USA
3 - USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 N 500 E, Provo, Utah, 84606, USA
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Presentation Type: Oral Paper:Papers for BSA Sections
Location: Cottonwood C/Snowbird Center
Date: Monday, July 27th, 2009
Time: 10:15 AM