The sagebrush steppe is a patchwork of species and subspecies occupying distinctenvironmental niches across the intermountain regions of western North America. These ecosystems facedegradation from disturbances and exotic weeds. Using sagebrush seed that is matched to its appropriateniche is a critical component to successful restoration, improving habitat for the threatened greater sage-grouse and other species. The need for restoration is greatest in basin habitats composed of two subspecies:diploid basin big sagebrush (A. tridentatasubsp.tridentata) and tetraploid Wyoming big sagebrush (subsp.wyomingensis). In this study we assess seed weights across five subspecies-cytotype groups of bigsagebrush and examine the genetic and environmental components. Our goal is to determine if seedweight can be used as a diagnostic test for subspecies and seed certification. Seed weight was measuredfrom 55 wild collections and from progeny derived from these collections and grown in two commongardens. A linear mixed-effect model showed 91%of the variation in seed weight is explained by genetic,genetic3environment and environmental effects (conditionalR2¼0.91). Moreover, genetic effects alone,subspecies-cytotype groups, explained 39%of the variation (marginalR2¼0.39). Of the five subspecies-cytotype groups, most had overlapping weights using conservative 99%confidence intervals. However,diploidtridentataandwyomingensishad non-overlapping 99%confidence intervals. To demonstrate theapplication of seed weighing to assess the subspecies purity of commercial seed lots, we comparedconfidence intervals oftridentataandwyomingensisdeveloped from the experimental data to seed weightsof commercial lots. The results showed that only 17%of the commercial seed lots certified aswyomingensishad mean seed weights that fell within the confidence intervals for this subspecies. The remaining lighterseed lots (83%) matched weights oftridentata. While restoring sagebrush ecosystems is a multifacetedproblem, a fundamental component to restoration is ensuring the appropriate seed is used. We found seedweight is principally affected by genetic factors, with limited environmental effects. Seed weighing is aneffective application to assess subspecies purity ofwyomingensisandtridentataseed and could be used as acertification step for evaluating commercial collections used in restoration.
