Identifying the geographic origins of invasiveMegathyrsus maximusin the United States using molecular data

Abstract

Guineagrass is non-native 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 Guineagrass samples from its native range in Africa and compared them to USA 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. 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 a Guineagrass 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 Guineagrass. Management Implications: The results of this genetic analysis identify native range origins of invasive Guineagrass in south Texas, allowing for potential to find highly host-specific biological control agents that will attack the invasive short form of Guineagrass and not attack the desirable tall form that is a valuable forage in the neoptropics.