After Russian wheat aphid (RWA) was first detected in Australian cereal crops in May 2016, considerable new knowledge has emerged from Grains Research and Development Corporation (GRDC) research investments activated in the wake of the pest’s discovery.
Now present in parts of South Australia, Victoria, Tasmania, and southern New South Wales, RWA is the focus of several unprecedented GRDC-supported research undertakings aimed at helping the grains industry combat the pest.
The GRDC has been investing in research to confirm susceptibility of commercial wheat and barley cultivars to RWA, assessing potential sources of plant resistance, determining aphid biotype, RWA biology, ecology, and economic thresholds under Australian conditions, an investigation into alternate hosts for RWA, trials looking at insecticide efficacy, and development of practical resources for growers and advisers.
GRDC Manager of Disease Traits, Lauren Du Fall, is overseeing key host resistance-related experiments – the first of their kind in Australia – being carried out by the South Australian Research and Development Institute (SARDI*) and led by entomologists Greg Baker and Maarten van Helden.
One of those projects has involved assessing RWA susceptibility of current commercial varieties.
“A total of 85 Australian commercial lines have been screened for RWA susceptibility at the seedling to tillering stage,” Dr Du Fall says.
“A range of symptom expression was observed in a preliminary screen of a selection of current commercial bread wheat, barley, and durum wheat varieties, indicating that there may be a level of tolerance or resistance present in current commercial cultivars that could be further developed.
“However, susceptibility to RWA is a complex assessment and further data will be required to confirm these results, assess the impact on yield and determine whether it will be valuable to provide resistance ratings of varieties.”
Another undertaking has focused on assessing sources of RWA plant resistance.
A glasshouse experiment has been conducted where diverse germplasm from around the world was screened with RWA to determine potential sources of resistance that might be utilised in breeding new varieties.
“Through assessing sources of resistance and the biotyping work, it appears we have access to germplasm with potential genetic resistance that could be developed through breeding to deliver Australian grain growers new resistant varieties if that is considered to be an economically viable and sustainable approach to controlling RWA by commercial breeding companies,” Dr Du Fall says.
“We are really getting on the front foot here to provide breeders and industry with all of the information necessary to make informed decisions on the most appropriate strategy to manage RWA as an endemic pest to south-eastern Australia.”
Some of the germplasm screened exhibited higher levels of resistance than those of current commercial cultivars.
Although the plant resistance research is generating encouraging insights, Dr Du Fall says it must be remembered that while plant resistance has been deployed as a management strategy in areas of the world where RWA is a serious risk, the aphid has responded through the evolution of new biotypes attacking these resistant plants.
The GRDC is therefore emphasising that genetic plant resistance will not be “the solution” to RWA control, but it may instead form part of an integrated pest management strategy that includes green bridge management, agronomic practices, strategic use of insecticides, and exploitation of natural enemies of the pest.
While the introduction of RWA presents yet another pest for growers to control, experts supported by the GRDC believe it should be a manageable pest.
In 2017, growers are advised to assess local risk and adopt a threshold-based management strategy. Managing the green bridge well prior to sowing will be an important tool to minimise exposure to RWA pressure in 2018.
More information on management of RWA and links to relevant resources are available via the GRDC website at www.grdc.com.au.
* SARDI is a division of Primary Industries and Regions South Australia (PIRSA)