Choose varieties carefully to reduce rust risk
To minimise the risk of crop damage from rust in wheat and barley in 2014, Western Australian growers need to think carefully about the varieties they retain now for crop seed, or plan to source.
Controlling the ‘green bridge’ and monitoring summer regrowth for rust is also imperative.
This follows the identification of wheat and barley leaf rust pathotypes new to WA – by the Grains Research and Development Corporation (GRDC)-supported Australian Cereal Rust Control Program (ACRCP) at the University of Sydney, with support from the Department of Agriculture and Food (DAFWA).
Based on reactions in eastern Australia, the findings – announced in recent months – could have significant implications for commonly grown varieties including Mace - by far the State’s most popular wheat variety.
The full extent of any changes in the rust resistance of different varieties will not be confirmed until more exhaustive tests have been completed.
Wheat leaf rust
Growers need to be aware of the potential changes to wheat leaf rust resistance ratings to make informed decisions now about what varieties to retain this harvest or to source.
Professor Robert Park of the ACRCP recently identified an eastern Australian wheat leaf rust pathotype (76-1,3,5,7,9,10,12 +Lr37) from samples collected across WA’s grainbelt.
This is expected to result in several wheat varieties becoming more susceptible to leaf rust.
Varieties that carry the Lr13 gene (such as Mace, Wyalkatchem, Corack and Emu Rock) and Lr17a (Fortune) will be more susceptible and may require additional management in 2014.
The resistance ratings of Mace and Wyalkatchem may be reclassified from resistant to moderately resistant (R-MR), to moderately susceptible (MS).
Some varieties have other leaf rust genes that are expected to still be effective so have a lesser rating shift.
These include King Rock, Fortune and Zippy that are likely to be reclassified from resistant to moderately resistant (R-MR) to moderately resistant to moderately susceptible (MR-MS).
The responses of Carnamah (MS) and Cobra are not likely to change, but further tests are needed to establish their responses more accurately.
Resistance ratings for all other wheat varieties are unlikely to change.
For example, Magenta, Sapphire and Bullaring remain resistant (R) to leaf rust in WA.
Information about other wheat disease resistance ratings is available in the WA Wheat Variety Guide 2013, available on the DAFWA website www.agric.wa.gov.au
When consulting this guide, growers should keep in mind the possible revisions to resistance ratings outlined above.
Disease information is also available on the GRDC-supported National Variety Trials website www.nvtonline.com.au
Barley leaf rust
A new pathotype of the barley leaf rust pathogen (Puccinia hordei) was identified by Prof Park, based on samples collected by DAFWA in WA’s southern cropping regions in 2013.
The new pathotype (5457 P-) is expected to reduce resistance to leaf rust in several varieties known to carry the Rph3 resistance gene in WA.
Test are underway to assess its impact on Bass, Fairview, Finniss, Fitzroy, Grange, Henley,Oxford ,Wimmera, and Yarra, barley varieties.
In barley leaf rust-prone areas such as the South Coast, Bass is likely to require careful management of leaf rust, comparable to existing susceptible varieties.
However, the leaf rust susceptibility of three of these varieties – Grange, Henley and Oxford – is not expected to change markedly due to the additional presence of the adult plant resistance gene Rph20.
Information about other barley disease resistance ratings can be found in the 2013 WA Barley Variety Guide on the DAFWA website.
Researchers recommend that all growers develop a rust management strategy for 2014.
Information on developing a strategy can be found on the Rust Bust website www.rustbust.com.au, which includes a ‘Rust Bust Management Checklist’, or in the GRDC Cereal Fungicides Fact Sheet at www.grdc.com.au/GRDC-FS-CerealFungicides.
Growers need to control the green bridge in coming months. But if leaf rust is detected on any regrowth, samples should be sent to the University of Sydney Plant Breeding Institute for pathotype analysis.
Rusted plant samples can be mailed in paper envelopes, not plastic wrapping or plastic-lined packages to the Australia Cereal Rust Survey Plant Breeding Institute, Private Bag 4011, Narellan, NSW, 2567.
The ACRCP is supported by growers through the GRDC.
It is one of the GRDC’s core investments to monitor, assess and develop a rust management strategy for Australian growers.Since the early 1970s, ACRCP researchers have identified new sources of rust resistance and have assisted breeders to incorporate these into new cereal cultivars.
The work has included extensive testing of cereal lines with new rust pathotypes to ensure industry-wide preparedness to the emergence of new rust threats.
This ensures that plant breeders are provided with new sources of leaf rust resistance to breed into new Australian wheat varieties.
PHOTO CAPTION: Peter Roberts