Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 12, 2008
Publication Date: May 4, 2009
Citation: Ashley, M.C., Longland, W.S. 2009. Assessing Cheatgrass (Bromus tectorum) Genetic Diversity and Population Structure Using Rapd and Microsatellite Molecular Markers. Western North American Naturalist. 61(1):63-74. Interpretive Summary: Two molecular marker systems, random amplified polymorphic DNA (RAPD) and microsatellites, were used to characterize the genetic diversity and population structure of cheatgrass from four northern Nevada sites. Both marker systems proved useful in assessing population genetic variation. One population-specific RAPD marker and six new microsatellite length polymorphisms were identified, some of which were population-specific. RAPDs proved most useful in revealing genetic diversity in populations that had low microsatellite diversity. Microsatellite markers were successful in identifying heterozygous individuals, products of cross-pollination, an important aspect regarding the production of offspring that may be able to colonize new habitats or spread more widely within areas where cheatgrass presence is marginal. Assessment of population structure and unique characteristics is important for identifying resistance to disease, pesticide, or bio-control agents. Both marker systems may as well prove useful in studying other closely related species such as red brome (Bromus rubens).
Technical Abstract: Two molecular marker systems, random amplified polymorphic DNA (RAPD) and microsatellites, were used to evaluate population diversity and differentiation in four northern Nevada Bromus tectorum populations. We found 16 RAPD primers that yielded 165 strong repeatable bands. Of those bands, 60 (35.8%) were polymorphic. RAPD variation was moderate (average = 0.275 ± 0.030) ranging from 0.212 - 0.346. Microsatellite variation was similar (average = 0.234 ± 0.043) but varied more widely ranging from 0.009 - 0.551. All populations were out of Hardy-Weinberg equilibrium. RAPDs revealed significant differentiation (P < 0.0001) across populations while microsatellites only resolved two of the four populations. RAPDs revealed a considerable amount of variation in the two of the populations that had nearly identical microsatellite profiles. All individuals had unique RAPD phenotypes. We found 51 microsatellite genotypes across individuals, one representing 95.3% of the individuals in the Hot Springs-Truckee group and present at a lower frequency at Stillwater (29%). The UPGMA trees were similar in that the Stillwater and Peavine populations were grouped in both but the trees were not significantly correlated. One population-specific RAPD marker and six new microsatellite length polymorphisms were identified.