First report of Guineagrass smut caused by Conidiosporomyces ayresii in North America.
Guineagrass (Panicum maximum, synonym = Megathyrsus maximus) is native to Africa but has been introduced to many tropical regions for use as livestock forage. It is a significant weed problem for crop production in several areas of the southern United States and has been the focus of previous efforts for biological control. It is listed by the Florida Exotic Pest Plant Council as a category II invasive species. Guineagrass with inflated florets filled with gray-brown spore masses was found in multiple locations in Saint Lucie and Okeechobee counties in Florida, USA, in May 2015. When observed, nearly all spikelets on individual plants and all plants in the area were affected. Based on morphological characteristics, sequencing of the 28S rDNA and pathogenicity, the causal agent was identified as Conidiosporomyces ayresii. This is thought to be the first report of Guineagrass smut in North America, the causal agent of which could potentially be used as a biological control agent for this invasive species.