Uredo rangelii

Uredo rangelii
File:Eugeniareinwardtianarust.JPG
on Eugenia reinwardtiana
Scientific classification
Kingdom:	Fungi
Division:	Basidiomycota
Class:	Pucciniomycetes
Order:	Pucciniales
Family:	Incertae sedis
Genus:	Uredo
Species:	U. rangelii
Binomial name
Uredo rangelii J.A.Simpson, K.Thomas & Grgur. (2006)

Uredo rangelii, commonly known as myrtle rust, is a fungal plant pathogen native to South America that affects plants in the family Myrtaceae. It is a member of the fungal complex called the guava rust (Puccinia psidii)] group. The spores have a distinctive yellow to orange colour, occasionally encircled by a purple ring. They are found on lesions on new growth including shoots, leaves, buds and fruits. Leaves become twisted and may die. Infections in highly susceptible species may result in the death of the host plant.

As of late 2013, it is infecting around 179 species in New South Wales and Queensland, from 41 genera (around 46% of genera in the Myrtaceae) in Australia.

Taxonomy

The rust was first described scientifically in 2006 by mycologists J.A. Simpson, K. Thomas, and Cheryl Grgurinovic.

Development and symptoms

Myrtle rust is typically characterised by the appearance of urediniospores on the underside of the leaf, though urediniospores may also be found on the top of the leaf or on young stems. Initially, the disease appears as small purple or red brown flecks with a faint chlorotic halo on the leaf surface, which coalesce to form bright yellow pustules. As the rust develops, these pustules often fade to a grey brown colour. A high degree of pustule coalescence can result in distortion of the leaf. Myrtle rust also makes plants more susceptible to secondary infections, which may occur within days of the initial appearance of the pustules.

Favourable conditions that increase the infection rate include: new tissue; high humidity; free water on plant surface for more than 6 hours; moderate temperatures, around 15–25°C. Low light conditions (minimum of 8 hours) after spore contact can increase germination.

The main ways in which myrtle rust can be spread are by: the movement of infected plant material, the movement of contaminated equipment, wind, water and gravity, animals, humans and/or vehicles.

Myrtle rust may remain on a single host plant to complete its life cycle, which can be as short as 10–14 days.

As an invasive species in Australia

See also: Biosecurity in Australia

Myrtle rust was first recorded in Australia in mid-2010 and currently poses a major threat to the continent's ecosystem given that almost 80 per cent of Australian native trees are Mytraceae, most indigenous species rely on healthy trees for their survival. Additionally it poses a major threat to Australia's primary industry sector. Its current range includes much of the eastern coastal fringe of the Australian mainland.

Initial detection was in April 2010 in Gosford in the Central Coast region of New South Wales. It was initially quarantined and eradication thought viable. The New South Wales government spent $5 million attempting to eradicate the disease. However, efforts to contain it failed and it spread rapidly north and south along the eastern coast. In response to the increasing threat, a Myrtle Rust National Management Group was formed on 2 July 2010 with the aim of eradication however due to the extent of its spread at that point of time, the group conceded that it had become impossible to eradicate.

By December 2010, it had significantly spread north along the coast and recorded in South East Queensland with isolated cases in Far North Queensland cities of Cairns and Townsville. In January 2012, an isolated myrtle rust outbreak was reported in Victoria beginning in Melbourne's southern and eastern suburbs. Initial attempts to contain it were unsuccessful and by April, 2012 it had spread across much of the state via regional cities.

Host genera

Species within the following plant genera have been recorded with the infection:

• Acmena
• Agonis
• Angophora
• Asteromyrtus
• Austromyrtus
• Backhousia
• Callistemon
• Chamelaucium
• Choricarpia
• Decaspermum
• Eucalyptus
• Eugenia
• Gossia
• Lenwebbia
• Leptospermum
• Lophomyrtus
• Melaleuca
• Metrosideros
• Myrtus
• Pilidiostigma
• Rhodamnia
• Rhodomyrtus
• Ristantia
• Stockwellia
• Syncarpia
• Syzygium
• Tristania
• Ugni
• Uromyrtus
• Waterhousea
• Xanthostemon

Management

The original plan to eradicate myrtle rust was declared to be unfeasible by the Myrtle Rust National Management Group in December 2010. The Myrtle Rust Response Plan was cancelled and focus was placed on minimising the spread and the impacts on myrtle rust. The Australian Government, through the Department of Agriculture Fisheries and Forestry (DAFF), established the Myrtle Rust Coordination Group to manage the investment of $1.5 million of research funding. The management plan consists of six main sections: coordination and communication, immediate disease management, taxonomy and identity of the pathogen, potential impact and distribution, chemical control options and resistance breeding options. This management plan should be applied to all species in the Myrtaceae family, within all industries.

To minimise the risk of increasing the distribution of myrtle rust, several precautions can be undertaken. These precautions include: not moving plant matter from one site to another; minimising pathogen spread by arriving and leaving each site clean of the pathogen, and avoiding areas that may contain myrtle rust-infected plant matter.

External links

• Uredo rangelii in Index Fungorum