Location: Plant Physiology and Genetics ResearchTitle: Complex Ploidy Level Variation in Guayule Breeding Programs Author
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2010
Publication Date: 11/15/2010
Citation: Gore, M.A., Coyle, G.G., Friebe, B., Coffelt, T.A., Salvucci, M.E. 2011. Complex ploidy level variation in guayule breeding programs. Crop Science. 51:210-216. Interpretive Summary: Natural rubber is an important commodity in the global economy. The potential spread of South American leaf blight to rubber tree plantations in Asia, the prevalence of Type I latex allergy, and a projected global shortage of natural rubber by 2020 have revitalized interest in developing new rubber crops. Guayule, a perennial shrub native to desert regions in North America, is a promising alternative to the rubber tree for production of natural rubber in the southwestern United States. Genetic improvement of guayule through plant breeding requires determining the number of copies of the basic chromosome set or ploidy level in a large number of plants. However, the existing technique used to determine ploidy levels in guayule is laborious for even a modest number of samples. Thus, a fast and accurate method to determine ploidy level in guayule is needed for improvement of this species in a breeding program. To that end, flow cytometry, a rapid and simple method to indirectly estimate the number of chromosomes in plant cells, was adapted for ploidy level analysis in guayule. With the use of flow cytometry, guayule cultivars and lines were found to span a wide range of ploidy levels. The availability of a rapid method to determine ploidy level in uncharacterized germplasm will help to accelerate the rate of genetic improvement in guayule breeding programs.
Technical Abstract: Guayule (Parthenium argentatum Gray) is a potential source of natural rubber, but attempts to domesticate and cultivate this perennial crop for large-scale commercial production in the southwestern United States have been intermittent over the past century. Genetic improvement through modern plant breeding is needed to increase its yield potential and suitability for commercialization. Natural variation in ploidy levels among individuals is among the factors that slow the rate of genetic gain in guayule breeding programs, thus knowledge of ploidy in guayule germplasm would help to accelerate the development of stable, high yielding cultivars. To that end, we adapted flow cytometry—a rapid and simple alternative to laborious chromosome counting—for ploidy level analysis in guayule. With the implementation of flow cytometry, we examined the ploidy of 34 guayule accessions available from the National Plant Germplasm System. A natural polyploid series that ranged from diploid (2n=2x=36) to pentaploid (2n=5x=90) was detected, with 4x as the predominant ploidy. In addition, not all plants sampled from an accession had the same ploidy level, which shows that ploidy within an accession can be variable. Notably, linkage of ploidy level data to that of pedigrees uncovered complex ploidy variation in guayule breeding programs. Importantly, this work serves as the basis for future breeding efforts as well as quantitative trait loci analysis and genomewide association studies in guayule.