Support for the 'out-of-Southeast Asia' hypothesis for the origin of Australian populations of Radopholus similis (Cobb, 1893) (Nematoda: Pratylenchidae).

Radopholus similis is one of the world's ten most economically important plant-parasitic nematodes. It is especially a problem in banana cultivation, where the nematodes' feeding reduces yields and causes toppling disease. It has been suggested that the genus Radopholus Thorne, 1949 might have an Australian origin, but the native range of R. similis (Cobb, 1893) is not well known. Here we undertake a phylogeographical study of samples of R. similis from banana plantations down the eastern seaboard of Australia, with additional samples from Costa Rica and accessions from GenBank, to examine the origin of pest populations of R. similis. The lack of genetic diversity of R. similis within Australia, and its sharing of a worldwide pest haplotype, suggest that populations of R. similis in Australia were introduced from a single source population, most likely from the Southeast Asian region. This might not be the case in Africa, where extensive genetic diversity has been found.