A rust pathogen affecting the invasive Navua sedge (Cyperus aromaticus) in Australia – A fortuitous biocontrol agent?

Abstract

Navua sedge (Cyperus aromaticus), a perennial invasive sedge affecting beef, dairy and sugarcane industries in the Queensland wet tropics, is a target for biocontrol in Australia. Host specificity tests for a floret-infecting smut fungus Cintractia kyllingae and a leaf and stem infecting rust fungus Puccinia kyllingae-erectae, both native to Africa, are in progress at CABI, UK. In 2023, a rust fungus on leaves and stems of Navua sedge was reported from a grazing property in Topaz, northern Queensland. The rust was morphologically and genetically identical to P. kyllingae-erectae from Africa. Puccinia kyllingae-erectae was found to be widespread in the Atherton Tablelands, and in the coastal lowlands, from Innisfail in the south to Cape Tribulation in the north. Puccinia kyllingae-erectae killed 80–95% of the above ground foliage, although Navua sedge resprouts from underground rhizomes. The rust was not found on pasture species or other native sedge species indicating that it is host specific. Future studies will focus on determining the distribution, impact and host range of P. kyllingae-erectae in the field.