Ancient wheats resistant to root lesion nematodes
The wild, ancient ancestors of wheat are a vital key to solving the problem of root lesion nematodes in Australia, researchers now believe.
Root-lesion nematodes (RLN) are ubiquitous in northern grain-growing systems. Pratylenchus thornei, the most prevalent species in the north, can cause up to 70 per cent yield loss in susceptible wheat varieties.
Northern growers currently have no commercial wheat varieties that resist the ravages of RLN, and the massive yield losses they experience each year are of great concern to the industry.
However, wheat researchers at the Queensland Department of Agriculture, Fisheries and Forestry (DAFF) have discovered that ancestral wheat species, and indigenous wheats (called ‘landraces’) cultivated in ancient villages of the Middle East, appear to be resistant to P. thornei.
“We realised the resistances that aren’t available in modern commercial wheat varieties do exist in their ancient ancestors,” says Queensland DAFF plant pathologist and project leader Jason Sheedy. “Over time, these wild relatives must have adapted to certain local conditions, including RLN in the soil.”
The researchers started taking a closer look at these ancient varieties, hoping to source some novel genetic resistances to P. thornei, and possibly other northern species of RLN.
Their project is part of an innovative wheat pre-breeding program into genetic options for RLN control funded by the GRDC. The GRDC invests more than $1.5 million annually into RLN research that cuts across both genetic and management options.
Using ancient resistance genes identified and transferred into locally adapted elite lines by researchers and made available to Australian wheat breeding programs, breeders hope to generate new commercial wheat varieties that will have higher yields and reduced losses from P. thornei.
The power of resistance
RLNs are a species of microscopic roundworm that are likely endemic to the Fertile Crescent region in the Middle East where wheat cultivation began in about 8000 BCE. From there, the species probably spread around the world, with grain cultivation across North Africa, Europe, America and, finally, in Australia.
Researchers believe Australian wheat varieties were initially bred in the absence of RLN. This means new varieties are susceptible to RLN, lacking the resistance their wild ancestors once had.
Without resistance, RLN can cause extreme tissue damage and ‘lesions’ inside the roots of plants. Multiplying rapidly, they inhibit an intolerant plant’s ability to absorb water and nutrients such as nitrogen, phosphorus and zinc from the soil. This leads to stunted growth and a decrease in crop yields.
Since there are no available commercial wheat varieties with resistance to RLN, choosing varieties that are tolerant, such as EGA Gregory, is a good first step in managing their populations (see the 2014 Queensland Wheat Varieties Guide).
However, tolerant varieties are not effective in any long-term management strategy, says Dr John Thompson, from Queensland DAFF.
“While they can still yield well, growing them doesn’t fix the nematode problem,” he explains. “Tolerant plants remain susceptible, and nematodes will continue to multiply inside their roots.
“A resistant variety, however, will prevent build-up of nematode populations quite dramatically and will ultimately reduce populations of nematodes in paddocks,” Dr Thompson says.
“In ancient villages of the Middle East people used to grow landrace wheats, and over time they would select and keep using the better varieties,” Dr Thompson says. “These varieties would then have adapted to local conditions, including the presence of RLN in the soil.”
For the program, researchers sought out Middle Eastern landrace wheats and varieties that might have been selected for resistance in this way over millennia.
The research team selected several hundred varieties from the Watkins Landrace Wheat Collection, based at the John Innes Centre in the UK. This collection is extensive, consisting of about 1200 landrace wheat varieties selected from 32 countries by UK botanist A.E. Watkins in the 1920s and 1930s.
The selected varieties were then screened in glasshouse experiments, and the extent of their resistance was determined by the number of P. thornei remaining in the soil after the plants were grown in the glasshouse.
“We found several that had resistance to P. thornei,” Dr Thompson says. “So we selected the best ones of these, and are now working to cross their resistances into adapted wheat varieties for the northern region and for Australia generally.”
For the pre-breeding program, the future looks bright for developing wheat lines with better resistance to RLN. When most wheat varieties grown on northern region paddocks are RLN-resistant, Dr Thompson says, the RLN-related problems growers are experiencing will be substantially reduced. This heralds a brighter future for the wheat industry, thanks to the remnants of its ancient past.
Dr John Thompson
07 4639 8806
2014 Queensland Wheat Varieties Guide is available at: www.grdc.com.au/WheatVarietiesGuide-QLD
Region North, Overseas