Origins and diversity of exotic silverleaf nightshade (Solanum elaeagnifolium Cav.) present in Australia as determined by sequence analysis of a chloroplast DNA intergenic spacer region

Solanum elaeagnifolium Cav. (silverleaf nightshade) is a native perennial of the Americas present in Australia as a Weed of National Significance. Knowledge of the genetic diversity and origins of silverleaf nightshade in Australia may inform future programs that propose using geographic source specific biocontrols to mitigate the weed.Here we sequenced the trnS-trnG intergenic spacer in chloroplast DNA (cpDNA) from native and introduced populations of silverleaf nightshade to identify haplotypes representative of cpDNA lineages in the species distribution. We used network analysis to infer a genealogy among identified haplotypes and compared the array of haplotypes detected in Australia to those found elsewhere.Eleven silverleaf nightshade haplotypes were identified and parsimoniously arranged as a shallow star-like genealogy. Two of five haplotypes in Australia were also in the United States of America, Mexico and South Africa. A third haplotype prevalent in Australia and South Africa was absent elsewhere but previously reported from Paraguay. Presence of two haplotypes unique to Australia indicated our sample was insufficient to identify all cpDNA diversity in the native distribution. Haplotype diversity in Australia was similar to that elsewhere and showed no signs of diminished genetic diversity expected if foundered by few colonisers.We argue silverleaf nightshade in Australia originated from genetically diverse populations in North and South America. Silverleaf nightshade in Australia is likely at a late successional stage of colonisation, containing a variety of genetic backgrounds that may respond differently to various biocontrols. Our future work will explore additional genealogies to pinpoint geographic origins of silverleaf nightshade in Australia.