Epidemiology, impact and management of myrtle rust (Puccinia psidii) in lemon myrtle plantations

Abstract

Lemon myrtle (Backhousia citriodora) is a native Australian species whose leaves contain oil with the highest citral content (<98%) of any known plant in the world. The leaves are dried and milled for use in teas or as a spice; and steam distillation is used to extract the essential oil from the leaf material, which can be used as food flavouring, in aromatherapy products, or in cosmetics and toiletries. This developing Australian native food industry has grown considerably in recent years, both in Australia and overseas. However, the introduction of the rust fungus Puccinia psidii into Australia in 2010 is jeopardising its expansion and success.
The widely used commercial cultivar Limpinwood is highly susceptible to P. psidii and yield losses have been estimated to be up to 70% in untreated lemon myrtle plantations. The aim of this research
is to gain an understanding of: (1) the factors influencing the susceptibility of lemon myrtle to infection by P. psidii and how it infects and colonises this host; (2) the effect P. psidii infection has on the growth and yield of lemon myrtle; and (3) the influence of climatic factors and inoculum density on the incidence and severity of P. psidii in lemon myrtle plantations. This will assist with the development of an effective evidence-based forecasting system for this disease and enable more informed, effective and economically feasible management decisions to be made, particularly with regard to fungicide applications. In addition, newly obtained lemon myrtle germplasm will be
screened for resistance to P. psidii.