Host Range and Virulence of a Fungal Pathogen for Control of Giant Salvinia (<i>Salvinia molesta</i>)

Abstract

A teleomorph of the fungus Botryosphaeria rhodina (Berkeley et Curtis) von Arx, ( Br ) was evaluated as a bioherbicide for control of giant salvinia ( Salvinia molesta D.S. Mitchell) under greenhouse conditions and in small-scale field trials. We found that fungal mycelium was highly infective and could be rapidly produced (48+ h) in soy flour-cornmeal liquid media contained in shake flasks or fermenters. A dew period was not required to achieve infection and mortality of inoculated plants. A surfactant (Silwet L-77, a polyalkyleneoxide modified heptamethyl-trisiloxane) incorporated in the fungal formulation was required for Br to infect and kill plants. Infection and mortality occurred rapidly (within 48 h after treatment), and re-growth of treated plants did not occur. In replicated field trials, Br controlled giant salvinia ~95%. Br also infected other plants, such as common salvinia ( S. minima Baker), and Azolla filiculoides Lam., as determined in ongoing host range research. However, no symptomatology was observed on several economically important crop species, such as rice ( Oryza sativa L.), corn ( Zea mays L.), and several woody species such as bald cypress ( Taxodium distichum L.) and loblolly pine ( Pinus taeda L.) occurring in areas where giant salvina occurs that would be subject to contact with releases of Br . These results suggest that this teleomorph of Botryosphaeria rhodina has potential as a bioherbicide for controlling this onerous aquatic weed.