Polyploid polymorphism in the prairie grass big bluestem (Andropogon gerardii)

TitlePolyploid polymorphism in the prairie grass big bluestem (Andropogon gerardii)
Publication TypeConference Proceedings
Year of Publication1989
AuthorsKeeler, KH, Kwankin, B
EditorBragg, TB, Stubbendieck, J
PublisherUniversity of Nebraska Press
Conference LocationLincoln, NE
Accession NumberKNZ00242

A suprising number of plant species contain individuals of a variety of levels of polyploidy, so that the species is polymorphic for polyploidy. This paper considers possible general causes for this phenomenon in plants of the Great Plains of North America. First we compared the frequency of intraspecific polyploidy in three major plant families, Poaceae, Asteraceae, and Fabaceae. The majority of grass species (Poaceae) and the minority of composite and legume species (Asteraceae and Fabaceae) are polyploid polymorphic. The frequency of grass species with intraspecific polyploidy suggests shared causatin or at least shared tolerance of this character. Having established that the situation occurs frequently in grasses, we analyzed a single species, big bluestem, Andropogon gerardii, looking for information on the function of polyploid polymorphism. We used flow cytometry to determine amount of nuclear DNA per cell; In big bluestem this correlates with chromosome number. Individuals with 7 pg nuclear DNA had 2N=60 chromosomes, and were therefore hexaploid, since in Andropogon x=10. Most other individuals had approximately 10 pg nuclear DNA and 80 (occasionally 90) chromosomes. Seven-pg DNA individuals were predominatnt everywhere, but the frequency of higher polyploids (10 pg nuclear DNA) went from virtually 0 on the eastern end of the tallgrass prairie region to 40% at the western end. Within native prairies in the west, the full range of variation existed between sites. A recent origin for polyploid polymorphism is suggested in big bluestem and probably other Great Plains grasses, and the data seem most compatible with a transitional situation, although other explanations cannot be ruled out