The origin of the southern African biotype of Chromolaena odorata: strong evidence puts an old question to bed

The origin of the southern African biotype of Chromolaena odorata: strong evidence puts an old question to bed
Costas Zachariades1,2, Iain D. Paterson3
1Plant Protection Research Institute, Agricultural Research Council; 2School of Life Sciences, University of KwaZulu-Natal; 3Department of Zoology & Entomology, Rhodes University

The neotropical shrub Chromolaena odorata (Asteraceae) remains a major invasive alien plant in the subtropical regions of southern Africa. From early in the South African biological control research programme, initiated in 1988, it was evident that the form of C. odorata invading southern Africa (designated the SA biotype) differed from that invading other parts of the Old World (designated the Asian/West African or A/WA biotype). Furthermore, for many years no plants identical to the SA biotype were found during exploratory surveys for biocontrol agents in the Americas. These issues posed a problem for the biocontrol programme in that many of the insects and pathogens collected from other morphological forms of C. odorata developed sub-optimally on the SA biotype. In the late

1990s anecdotal evidence accumulated to indicate that this biotype originated from one of the islands in the northern Caribbean (collectively known as the Greater Antilles and including Jamaica and Cuba). A molecular study examining the ITS region was conducted in the early 2000s, but was inconclusive. In order to establish with confidence that the SA biotype originated in this region, and thus that biocontrol agents collected from this region would have a high degree of compatibility with the weed, the current molecular study, using ISSRs, was conducted. This study has provided strong evidence that the C. odorata invading southern Africa originates either from Jamaica or Cuba. Genetically, the Jamaica-Cuba-South Africa clade is highly distinct from C. odorata from other parts of its wide native range.