Genetic diversity of bluebunch wheatgrass cultivars and a multiple-origin polycross

Bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love = Agropyron s picatum Pursh: Poaceae) is a cross-pollinating perennial grass native to we stern North America. Two bluebunch wheatgrass cultivars, Goldar and Whitmar , are currently available for large-scale rangeland seeding. However, culti vars may lack the genetic diversity and adaptation necessary for dynamic no n-local environments. The objective of this study was to quantify and compa re genomic DNA variation within and between Goldar, Whitmar, and Generation 2 of P-7, a multiple-origin polycross (MOPX2) of 25 naturally diverse blue bunch wheatgrass collections. Ne assayed 1043 polymorphic amplified fragmen t length polymorphism (AFLP) products and 88 monomorphic AFLP products from three sample populations of 22 plants. The number of polymorphic loci (and unique alleles) within sample populations of P-7, Goldar, and Whitmar was 898 (99), 813 (49), and 746 (59), respectively. Conversely, the number of f ired AFLP loci within sample populations of P-7, Goldar, and Whitmar was 23 3, 318, and 385, respectively. The overall nucleotide-sequence diversity [p i +/- SE (x1000)] estimated for P-7, Goldar, and Whitmar was 100.2 +/- 7.1, 80.1 +/- 6.6, and 79.4 +/- 6.7, respectively. By all measures, genetic var iation within P-7 is significantly higher than genetic variation within cul tivars. However, the estimated number of inter-population nucleotide differ ences per site [d(x) +/- SE (x1000)] between Goldar and Whitmar, e.g., 36.6 +/- 1.6, is only slightly higher than pi within these cultivars, therefore the net nucleotide-sequence divergence [d(A) +/- SE (x 1000)] between thes e cultivars is relatively small, e.g. 2.5 +/- 0.3. These results indicate t hat selectively neutral genetic diversity has not been dramatically reduced or inadvertently lost via genetic drift that may ha ve occurred since the divergence of Goldar and Whitmar. No AFLP markers completely distinguish Go ldar and Whitmar, therefore discrete morphological differences between thes e cultivars (e.g., the presence and absence of awns) most likely result fro m natural or artificial selection.