Unintentional Selection and Genetic Changes in Native Perennial Grass Populations During Commercial Seed Production

For habitat restoration, seed of native plant species is frequently transferred over wide geographic areas and planted in environments that differ from the original collection environment. When such collections are grown for seed production in agricultural fields, the genotypes favored under agronomic conditions may differ from those favored at the eventual planting location. The resulting agronomically-produced seed may be poorly matched to intended restoration sites. Populations of two native perennial grasses commonly used in restoration projects in California were grown in typical agronomic conditions for seed production. We compared traits of the plants produced from seed harvested in the first and second years of agronomic production to plants produced from the original seed collections. We found strong evidence for genetic shifts in both species as a result of selection associated with biotic and abiotic factors. A four-population mixture of Elymus glaucus produced seed comprised mainly of two populations, primarily due to differential sensitivity to disease. With two populations of Nassella pulchra, early and late harvests selected for early and late maturing genotypes, respectively, and a reduction in the variance in phenology within the seed from the early harvest. We found that agronomic techniques for seed production have the potential to cause unintentional genotypic selection and result in shifts away from the genetic composition of the original seed collection. We offer recommendations for seed increase protocols to reduce these outcomes.