Genetic variation in the invasive pompom weed, Campuloclinium macrocephalum, in South Africa.
Campuloclinium macrocephalum (Asteraceae) is native to South and Central America but is a highly invasive weed in South Africa where it is commonly known as the pompom weed. It is a target for biological control and success will depend on host specificity and biotype compatibility with the full genetic diversity of pompom weed in South Africa. We investigated the Amplified Fragment Length Polymorphisms (AFLP) marker diversity in 54 South African, 25 Argentinean and three Brazilian specimens. AFLP analyses showed a close relationship between South African and South American populations, and greatest similarity between the Argentinean population and the South African Gauteng one. All specimens showed different proportions of genetic admixture between two genetic entities but with a low net nucleotide distance of 0.115. Although there was a significant genetic variation among the populations, genetic differentiation and mean heterozygosity were low indicating low genetic diversity between the populations. These results suggest some clonal reproduction has occurred, and at least 23 clones (16 in South Africa) were present among the populations, indicating that clones were introduced to South Africa more than once. A population-assignment analysis revealed that all the South African populations studied contained at least one individual that may have migrated from the Gauteng population. The original point of entry is therefore very likely Gauteng, with Argentina as the most probable source of the South Africa invasion. Long-distance dispersal appears to have played a major role in the spread of the weed across South Africa, as indicated by a weak positive non-significant genetic versus geographic structure. The AFLP results contrast with those of our previous studies based on ribosomal DNA Internal Transcribed Spacer (ITS) regions of 52 specimens from across South Africa, 14 Argentinean and three from Brazil which suggested that all specimens might be a single clone. Nonetheless, both ITS and AFLP markers confirm the close relationship between Argentinean and South African specimens and low genetic diversity among the various populations. Candidate Argentinean biological control agents may therefore be effective on South African populations of C. macrocephalum, and testing of the biological control agents should include populations from all invaded provinces.