Austropuccinia psidii (myrtle rust).

Abstract Austropuccinia psidii is a rust fungus with a wide and expanding host range within the Myrtaceae, with over 440 host species currently known (Carnegie and Lidbetter, 2012; Morin et al., 2012; Pegg et al., 2014). Like many rusts, urediniospores of A. psidii can be wind-dispersed over long distances. Viable spores have been detected on clothing and personal effects following visits to rust-affected plantations (Langrell et al., 2003), and this is a viable pathway for dispersal. Furthermore, there are several instances of (accidental) long-distance movement of A. psidii on diseased plants, both within and between continents (Loope et al., 2007; Kawanishi et al., 2009; Carnegie and Cooper, 2011; Zambino and Nolan, 2012). Under sub-optimal conditions, the rust can remain un-symptomatic within plants for more than a month (Carnegie and Lidbetter, 2012). This combination of wide host range and ease of long-distance dispersal make A. psidii a successful invasive pathogen. It has spread quickly once established in new countries, including Jamaica (MacLachlan, 1938), Hawaii (Uchida and Loope, 2009), Australia (Carnegie and Cooper, 2011; Pegg et al., 2014) and New Caledonia (DAVAR Nouvelle-Calédonie, 2014). Severe impact on a range of Myrtaceae has been recorded in amenity plantings, commercial plantations and the native environment. A. psidii was first identified as an invasive pathogen in the 1930s when it caused extensive damage to allspice (Pimenta dioica) plantations in Jamaica (Smith, 1935; MacLachlan, 1938). A. psidii has been identified as a quarantine risk for some time in many countries including Australia (Australian Quarantine Service, 1985; Grgurinovic et al., 2006), South Africa (Coutinho et al., 1998) and New Zealand (Kriticos and Leriche, 2008).