Submitted to: Grass Breeders Work Planning Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2003
Publication Date: 2/1/2004
Citation: Johnson, R.C., Bradley, V.L., Foiles, C.L. 2004. Regenerating grass germplasm: choosing the right compromise. Grass Breeders Work Planning Conference Proceedings. Interpretive Summary: The Western Regional Plant Introduction Station (WRPIS) maintains more than 17,000 forage and turf grass accessions. The majority of these are self-incompatible, wind-pollinated species with high levels of heterogeneity. Germplasm accessions received at the WRPIS usually require an initial seed increase before the quantity and quality of seed is adequate for storage and distribution to users for research purposes. The two main problems associated with regeneration of heterogenetic, outcrossing grass germplasm are 1) the potential for genetic contamination through unwanted crossing of wind pollinated accessions and 2) genetic drift associated with small population used for regeneration. Research at the WRPIS has shown how the potential for unwanted wind pollination can be reduced greatly with minimal distance isolation. Genetic drift can be substantially reduced though increasing plant populations and by special head sampling techniques during grass seed regeneration.
Technical Abstract: Genetic contamination through pollen flow was measured by using a dominant pubescent line and a recessive glabrous line in Bromus inermis Leyss. Genetic contamination from pollen measured from a central pubescent row to glabrous rows spaced 1.5 m apart averaged 17% at 1.5 m, but only 0.5% at 9 m distance. Contamination in plots adjacent and parallel to pubescent plots averaged 15.7% at 3 m distance. Contamination in plots located 1.5 m from the ends or 2.1 m diagonally from pubescent plots averaged only 4.8%, but ranged from 0.7% to 13.7%. Bromegrass marker plots integrated into seed regeneration nurseries at two locations resulted in average contamination of 4.2% at distances between 22 and 27 m. Distance and the abundance of non-contaminating pollen appeared to determine the extent of contamination. For regeneration plots, isolation distances of 22 to 27 m resulted in a relatively low level of contamination. Seed sampling methods to enhance effective population size help maintain the genetic diversity in heterogenetic populations were also developed. In diverse species of heterogenetic grass populations, sampling a constant number of inflorescences from each plant enhanced effective population size by reducing variation in seeds per plant. Most of this benefit was derived when only three to five inflorescences were sampled. Inflorescence sampling appeared to be a cost effective method to help maximize effective population size and diversity of heterogenetic populations during seed regeneration. Potential applications include seed regeneration at gene banks, field germplasm collection, and in selection programs, when maintaining population diversity is desired.