A potential biocontrol agent for Alternanthera philoxeroides
Alternanthera philoxeroides (Amaranthaceae) known as alligatorweed, is an aquatic perennial plant native to South America and is invasive in freshwater systems around the world. In the EPPO region, it is not widespread and is only recorded in the wild in France and Italy. It alters the ecology of infested sites, restricting light penetration which interfers with the growth of submerged flora and fauna and has also been found infesting crops and pastures.
Although biological control with Agasicles hygrophila (Coleoptera: Chrysomelidae) and the moth Arcola malloi (Lepidoptera: Pyralidae) is successful in aquatic habitats, there is a need for additional agents to manage the weed in large infestations of natural ecosystems. Accordingly, in a survey in Brazil in 1997, the fungus Nimbya (=Alternaria) alternantherae was discovered and confirmed to be highly damaging to A. philoxeroides. Studies were conducted to determine the potential of this fungus for controlling this weed. Several isolates from Brazil, USA and Puerto Rico were compared and no differences in virulence were observed (although a lower dew requirement was demonstrated for the Brazilian isolates). Conidia were more effective than mycelial suspension, and inoculum concentrations of 1x105 and 1x106 conidia per ml provided significant levels of control of the weed in greenhouse and field experiments, respectively. In a host-range study, Nimbya alternantherae infected five other plant species from a total of 42 species belonging to 23 families. These five species are Celosia cristata and C. plumosa (Amaranthaceae), Beta vulgaris (sugar beet) and Spinacia oleracea (spinach) (Chenopodiaceae) and Portulacca halimoides (Portulacaceae). Therefore, if a commercial mycoherbicide based on N. alternantherae is developed, and further studies confirm its pathogenocity to cultivated plants, particularly celosia (e.g. an important species for the cut flower industry in Florida), spinach and beet, it will be necessary to clearly indicate on the label that the product should not be sprayed on these crops. N. alternantherae has the potential to be an effective mycoherbicide for A. philoxeroides.
Pomella AWV, Barreto RW, Charudattan R (2007) Nimbya alternantherae a potential biocontrol agent for alligatorweed, Alternanthera philoxeroides. Biocontrol 52(2), 271-288.