Exploring Origins, Invasion History and Genetic Diversity of Imperata cylindrica (L.) P. Beauv. (Cogongrass) using Genotyping by Sequencing

Imperata cylindrica (Cogongrass) is a diploid C4 grass that is a noxious weed in 73 countries that constitutes a significant threat to global biodiversity and sustainable agriculture. In the southeastern United States alone, this species has invaded over 1.5 million acres. Repeated herbicide application has failed to control Cogongrass, which annually expands its invaded range. Using a genotyping-by-sequencing (GBS) approach, we surveyed over 500 Cogongrass samples from affected areas across the southeastern United States and from potential regions of origin overseas. The species I. brasiliensis, collected in both Florida and multiple sites in Brazil, was included in the analysis to determine if hybridization between I. cylindrica and I. brasiliensis has occurred. We employed the sequenced crop species Sorghum bicolor (L.) Moench as a proxy reference genome to identify a set of 2,320 informative single nucleotide and insertion-deletion polymorphisms. Genetic analysis identified four clonal lineages of I. cylindrica and one clonal lineage of I. brasiliensis in the United States. Each lineage was highly homogeneous, and we found no evidence of hybridization among the different lineages. We found evidence that three of these lineages show clonal reproduction prior to introduction to the United States. We observed greater clonal diversity in populations collected in Africa and Asia. These results indicate Cogongrass infestations in the US have limited evolutionary potential to adapt to novel environments and are excellent candidates for biological control strategies.