Identifying the geographic origins of invasive Megathyrsus maximus in the United States using molecular data.

Megathyrsus maximus is nonnative in the neotropics, with a tall form that is commonly used as a forage grass and a smaller-statured form that is considered invasive in south Texas, USA. Biological control researchers are challenged to find an agent that will attack the short form, but not the desirable tall form in other parts of the neotropics. We conducted molecular analyses on 155 Megathyrsus maximus samples from its native range in Africa and compared them with U.S. short-form samples to help determine the geographic origins of its invasion. We found eight distinct genotypes in 34 short-form samples from Texas and Florida, USA. The highest genetic similarity of invasive samples was with plants from South Africa, while highest matches for the desirable tall form were from Kenya, Uganda, Ivory Coast, and Zambia. Ongoing biological control agent exploration and research has found agents from Kenya that are associated with an M. maximus genotype not well matched to the invasive short form, thus leading to a lack of rearing success. Two eriophyoid mite agents from the genetic match locality in South Africa have been evaluated but are not sufficiently host specific, as they develop on both the short and tall forms. Additional exploration is needed at the genetic match populations in South Africa to discover and evaluate potential biological control agents for the invasive form of M. maximus