Couch smut, an economically important disease of Cynodon dactylon in Australia

Abstract

Couch smut, caused by Ustilago cynodontis, is an economically important disease of Cynodon dactylon, the most widely planted warm season turfgrass in Australia. The disease is distributed across all states and mainland territories of Australia, and is found worldwide wherever the host plant is present. The most characteristic disease symptoms are expressed at the flowering stage, when the inflorescence is partly or entirely destroyed and covered by a mass of black powdery spores. However, there are also less obvious impacts of the disease on plant growth such as a more erect growth habit, and a reduced rate of stolon extension and root development, leading to lower levels of tolerance of the turf to wear during usage, and greater amounts of wastage during harvest due to the roll breaking at points of infection. Ustilago cynodontis was first described nearly 130 years ago but pathogen biology and disease epidemiology are still poorly understood, hindering development of disease management strategies. We review the current knowledge and understanding of couch smut biology, the history of its occurrence, distribution and impact, and existing disease management practices to identify the gaps in knowledge that require further research.