Exploring origins, invasion history and genetic diversity of Imperata cylindrica (L.) P. Beauv. (Cogongrass) in the United States using genotyping by sequencing

Authors: BURRELL, MILLIE - Texas A&M University; PEPPER, ALAN - Texas A&M University; HODNET, GEORGE - Texas A&M University; Goolsby, John; OVERHOLT, WILLIAM - University Of Florida; RACELIS, ALEXIS - University Of Texas Rio Grande Valley; DIAZ, RODRIGO - University Of Florida; KLEIN, PATRICIA - Texas A&M University

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2015
Publication Date: 7/1/2015
Citation: Burrell, M., Pepper, A.E., Hodnet, G., Goolsby, J., Overholt, W., Racelis, A.E., Diaz, R., Klein, P. 2015. Exploring origins, invasion history and genetic diversity of Imperata cylindrica (L.) P. Beauv. (Cogongrass) in the United States using genotyping by sequencing. Molecular Ecology. 24:2177-2193.

Interpretive Summary: Imperata cylindrica (Cogongrass) is an invasive grass that is a noxious weed in 73 countries and constitutes a significant threat to global biodiversity and sustainable agriculture, especially in the south-eastern United States. A cost-effective genotyping (DNA fingerprinting) approach to identify the geographic origins of invasions in the U.S. In this work, we demonstrated the advantage of using genetic tools that had previously been developed for a closely related crop species, Sorghum bicolor (L.) Moench (sorghum, milo). The genetic analyses identified. four separate lineages of cogongrass in the United States. Each lineage was very similar genetically, and we found no evidence of hybridization among the different lineages, despite the fact that the populations of the grass sometimes overlapped geographically. At least three of these lineages showed clonal reproduction (genetically identical) prior to introduction to the United States. These results indicate that cogongrass has limited evolutionary potential to adapt to new environments, and yet presents a clear case of broad invasive success, across a diversity of environments, of a clonal organism with limited genetic diversity. This research also shows that finding the origin(s) of these specific clonal lineages of U.S. cogongrass could lead to selection of the best adapted biological control insects for a biological control program.

Technical Abstract: Imperata cylindrica (Cogongrass, Speargrass) is a diploid C4 grass that is a noxious weed in 73 countries and constitutes a significant threat to global biodiversity and sustainable agriculture. We used a cost-effective genotyping-by-sequencing (GBS)approach to identify the reproductive system, genetic diversity and geographic origins of invasions in the south-eastern United States. In this work, we demonstrated the advantage of employing the closely related, fully sequenced crop species Sorghumbicolor (L.) Moench as a proxy reference genome to identify a set of 2320 informative single nucleotide and insertion–deletion polymorphisms. Genetic analyses identified four clonal lineages of cogongrass and one clonal lineage of Imperata brasiliensis Trin. In the United States. Each lineage was highly homogeneous, and we found no evidence of hybridization among the different lineages, despite geographical overlap. We found evidence that at least three of these lineages showed clonal reproduction prior to introduction to the United States. These results indicate that cogongrass has limited evolutionary potential to adapt to novel environments and further suggest that upon arrival to its invaded range, this species did not require local adaptation through hybridization/introgression or selection of favourable alleles from a broad genetic base. Thus, cogongrass presents a clear case of broad invasive success, across a diversity of environments, in a clonal organism with limited genetic diversity