Genetic variation within and among silverleaf nightshade (Solarium elaeagnifolium Cav.) populations in South Australia

摘要

Native to America, silverleaf nightshade (Solanum elaeagnifolium Cav.) has become a major agricultural weed across the globe. Since its introduction to Australia in the early 1900s the weed has spread across much of the south-east temperate zone. Theextensive root system of silverleaf nightshade allows it to survive most cultural and chemical control measures and regenerate from rootstock. Given the difficulty in controlling this weed, containment to prevent this weed spreading to unaffected areas should be the focus of control programs. Silverleaf nightshade infestations can increase in size through regeneration from the creeping root system, but spread over longer distances is thought to be a result of root fragment and seed dispersal. Genetic analysis tools were used to investigate mechanisms of spread of silverleaf nightshade. Leaf material was collected from silverleaf nightshade populations across the range of the species in South Australia and extracted for analysis with a RAPD marker. Analysis of genetic variation within populations indicated that most of the populations examined contained multiple genotypes, highlighting that sexual recombination and dispersal of seeds may play important roles in maintaining genetic diversity within populations. Examination of genetic variation within and between populations at property, regional and state levels also highlighted that outcrossing occurred and that dispersal of seed was the major factor in the spread of silverleaf nightshade across larger areas. Differentiation between populations indicated that gene flow was not at adequate levels to counteract genetic drift within populations, resulting in significant genetic diversity across the state. The amount of genetic variation present in silverleaf nightshade in South Australia alone indicates that there were repeated introductions of the weed to the state and the random distribution of genotypes across the state implies that longer distance dispersal of the weed probably by seeds, has occurred. Figure 1 highlights the apparent lack of correlation between pairwise comparisons of genetic and geographical distance between populations sampled across South Australia. The key role that seed appears to play in the spread of silverleaf nightshade within and among populations in South Australia emphasises the need to prevent seed set and the movement of contaminated agricultural produce, livestock and machinery in order to contain this weed. The significant levels of genetic diversity identified insilverleaf nightshade in South Australia alone also has important implications for the long term management of this weed, in terms of the potential evolution of resistance to control mechanisms.