Development of an Australian Standard Myrtle Rust Impact Rating Models

Michael Cole of the Australian Government Department of Agriculture, Fisheries and Forestry is leading this project towards the development of a standardised rating system for Myrtle Rust

The rating system is the subject of vigorous discussion and varying approaches. A key requirement is support for a range of user experiemce to maximise the quality of the information captured while not excluding willing stakeholders through excessive complexity and detail.

In Australia there are about 88 genera and 2253 species of native Myrtaceae plus a significant, but not yet tallied, number of exotic genera and species. Potentially most of these could be susceptible to myrtle rust. It is clearly not feasible to develop specific methodologies for each genus or species (suhc as the first example below). Furthermore the variation in susceptibility between hosts is enormous, ranging from one or two sori per plant in some Callistemon populations, to near total defoliation in some Rhodamia. The methodology to be used on this website has to be able to encompass this very wide variation in disease intensity between hosts, and perhaps between sites, yet provide accurate and reproducible data.

Option 1: Disease Index for the Rust Puccinia psidii sensu lato on Rhodamnia species in Australia

The rating system shown here is being developed for potential use in a QLD/NSW CRC project using Rhodamnia in a sentinel site approach.

OPTION 2: Myrtle rust disease severity Index - Jack A. Simpson Biosecurity Australia 23 June 2011

The rating system shown here provides some valuable context to the ongoing discussion on MR measurement methodologies in seeking to develop a National consensus standard.

Other Options

This CSIRO and NSW Departmentof Primary Industries Report - Myrtle rust: host testing under controlled conditions - provides both a detailed analysis of host infections but also includes another assessment option.

EXTRACT Myrtle rust (Uredo rangelii) was first detected in Australia in April 2010. This exotic plant pathogen belongs to the guava/eucalyptus rust complex (Puccinia psidii sensulato), which is native to South and Central America and known to have a very wide host range within the Myrtaceae family. Rusts in this complex only infect young, actively-growing foliage, as well as floral buds and young fruits in some hosts. As part of the nationally-funded interim response plan for myrtle rust, the National Management Group agreed to fund a project, with co-investments from CSIRO and NSW Department of Primary Industries, to obtain better understanding of the host range potential of myrtle rust by undertaking a series of experiments under controlled conditions.

These earlier references have inspired Australian thinking on assessment models:

Disease Index for the Rust Puccinia psidii on ��hi�a Metrosideros polymorpha) in Hawai�i, and EXTRACT A rust disease first found on potted ��hi�a (Metrosideros polymorpha) on O�ahu in 2005 has become a threat to Hawai�i�s forests. This plant composes as much as 80 percent of some of the remaining native forests, and its genetic diversity is highly valuable to these ecosystems. ��hi�a is one of the first plants to colonize new lava flows and is adapted to both wet and dry environments from sea level to high elevations. As a keystone species in the forest, ��hi�a provides habitat for numerous populations of native flora and fauna, including some endangered species, and helps maintain the hydrological cycle; without it, the entire ecosystem is at risk.

Disease Index for the Rust Puccinia psidii on Rose Apple in Hawai�i. This rust rating severity/impact rating approach uses methodologies prepared by University of Hawaii at Manoa for assessing guava rust disease intensity on two host species Metrosideros polymorpha and Syzygium jambos.