Assessing Cheatgrass (Bromus tectorum) Genetic Diversity and Population Structure Using Rapd and Microsatellite Molecular Markers

Abstract

Two molecular marker systems, random amplified polymorphic DNA (RAPD) and microsatellites, were used to evaluate population diversity and differentiation in 4 northern Nevada Bromus tectorum populations. From 80 RAPD primers, we found 16 (20%) that yielded 165 strong repeatable bands. Of those bands, 60 (35.8%) were polymor- phic. Of those, 21 met data-pruning guidelines for final analysis. RAPD variation was moderate (x = 0.363, s x -= 0.022), ranging from 0.312 to 0.404. Microsatellite variation was similar ( x - = 0.234, s x 0.051) but varied more widely, rang- ing from 0.009 to 0.551. All populations were out of Hardy-Weinberg equilibrium, as expected in a predominantly self- ing species. RAPDs revealed significant differentiation (P < 0.0001) across populations, whereas microsatellites only resolved 2 of the 4 populations. RAPDs revealed a considerable amount of variation in the 2 populations, Hot Springs and Truckee, which had nearly identical microsatellite profiles. Of 184 individuals, we found 182 unique RAPD pheno- types. We found 51 microsatellite genotypes across individuals, one of which was present in 95.3% of the individuals in the Hot Springs-Truckee group and 29% of the Stillwater individuals. The UPGMA phenograms were similar in group- ing Hot Springs with Truckee, and Stillwater with Peavine, and were highly correlated but not significantly. Both marker systems proved useful in assessing population genetic variation. One population-specific RAPD marker and 6 new microsatellite-length polymorphisms were identified. Both marker systems may also prove useful in studying other closely related species such as red brome (Bromus rubens).