Western Australia
October 9, 2013

A leaf rust pathotype that can overcome resistance in barley cultivars carrying the Rph3 gene has recently been detected for the first time in WA.

The pathotype (known as 5457 P-) was identified by Robert Park at the GRDC-funded Australian Cereal Rust Control Program (ACRCP), based at the University of Sydney’s Plant Breeding Institute (PBI).

It was found during testing on seven barley crop samples collected in September 2013 from Boxwood Hill, South Stirling, Chillinup and Kamballup in conjunction with the Department of Agriculture and Food WA (DAFWA).

This newly-detected pathotype will primarily affect the Bass variety - commercially released this year - and advanced breeding lines in WA that carry the resistance gene Rph3.

This is the first time Rph3 resistance has been compromised in barley varieties in WA, highlighting the importance of the GRDC’s national rust detection and control initiative through the ACRCP and in close collaboration with DAFWA.

The pathotype 5457 P- is one of several mutations of the barley leaf rust pathogen Puccinia hordei to be identified nationally by PBI through the ACRCP during the past five years.

Professor Park is now testing advanced breeding lines carrying the resistance gene Rph3 to assess the full impact of the new 5457 P- pathotype and its potential future risks to WA barley varieties.

He says screening pre-breeding barley lines with new leaf rust pathotypes has been ongoing since 1997. Since 2009, this testing has included a pathotype from eastern Australia with virulence for Rph3, which is now common in north eastern grain growing regions of those States.

Research to incorporate new sources of leaf rust resistance into new Australian barley cultivars is also being undertaken through the ACRCP at the PBI.

This is targeting potentially more durable resistance sources that are effective at post-seedling growth stages, such as adult plant resistance.

Several Australian barley cultivars already contain adult plant resistance provided by the Rph20 gene. These include Flagship, Oxford, Grange, Henley, Shepherd and Westminster.

Cultivars affected by the new gene mutation

The specific new 5457 P- pathotype mutation is unique to WA, but it is expected to behave similarly to another pathotype with virulence to Rph3 that is present in eastern Australia (known as 5457 P+).

On this basis, it is likely to have the biggest impact on Bass, which has the Rph3 gene.

Grange, Henley and Oxford carry both the Rph3 gene and the Rph20 gene, which is expected to provide some residual resistance and should mean leaf rust response will not change significantly.

Further testing will assess the impact of 5457 P- on Fairview, Finniss, Fitzroy, Wimmera and Yarra varieties, which also have the Rph3 gene.

These varieties – and Bass - were rated as susceptible in PBI field tests from 2009-10 when challenged with the eastern States Rph3-virulent pathotype 5457 P+.

If the population of 5457 P- pathotype builds in WA, it is expected this mutant could migrate to the eastern States - but it is not expected to have an additional significant impact on cultivars there.

On-farm implications in WA

Growers of Bass, Oxford, Grange, Henley, Fairview, Finniss, Fitzroy, Wimmera and Yarra are being advised to monitor these crops closely.

Distribution of the new leaf rust pathotype outside the initial detection area is not yet fully understood. If any leaf rust is detected, it is recommended farmers contact their local DAFWA office.

Samples showing signs of leaf rust can also be sent to PBI for pathotype analysis (see details in Useful Resources below).

A wet and warm spring has exacerbated leaf rust problems in some southern areas of WA and, with higher disease incidence, there is potential for the new pathotype to spread.

Early detection, awareness and monitoring its distribution will allow DAFWA, GRDC and the grains industry to direct research to the most needed areas.

DAFWA researchers are advising growers in leaf rust-prone areas, such as the South Coast, to be aware that future plantings of Bass will require careful management of leaf rust – similar to that used for existing susceptible varieties.

They are also recommending that growers in leaf rust prone areas be extra vigilant about controlling all varieties of barley volunteer crops in the lead-up to 2014 crop plantings, especially if there is a wet summer.

Further information about rust, control and new pathotype mutations can be found through GRDC’s The Rust Bust website: www.rustbust.com.au and the ACRCP.

Website: http://www.grdc.com.au

Published: October 9, 2013