Closing in on the first wheat varieties in the world resistant to barley yellow dwarf virus (BYDV), CSIRO and Queensland Department of Primary Industries researchers have enjoyed a series of pleasant surprises on the disease resistance front.
A Hartog-like spring wheat QT8733, to be released this year, and a winter wheat known as LH64C, due for release in 2003, will be the first commercially available BYDV-resistant wheat varieties. The virus resistance came from a wild wheat grass, Thinopyrum intermedium.
QDPI researchers at Toowoomba recently discovered that resistance to the nematode Pratylenchus thornei has been transferred to QT8733 from Thinopyrum along with the virus resistance. Further, Thinopyrum, known as intermediate wheat grass, also carries and may hold the key to new genes for rust resistance.
New high-'rainfall wheat
CSIRO plant breeder Susan Kleven says that, last year in trial plots at Millthorpe on the NSW Central Tablelands where BYDV was particularly severe, LH64C out-yielded all other varieties by 40 per cent. The research is supported by growers through the GRDC.
Across 11 sites in the high-rainfall wheatbelt the variety averaged 5.62 t/ha and produced 19 per cent more than the average of the highest-yielding commercial winter wheat variety, Declic.
She estimates that an autumn infestation of BYDV can reduce yield potential by more than 30 per cent.
The wild perennial grass Thinopyrum intermedium is a native to Iran, Iraq and China. CSIRO Plant Industry’s Phil Larkin developed the original germplasm with Phillip Banks of QDPI’s Leslie Research Centre.
Dr Larkin says the fact that the grass is a perennial is important and is the reason that it has built up such a high level of disease resistance. His work, begun in 1988, is being described as an unconventional use of conventional plant-breeding techniques.
The original crosses between wheat and the grass parent produced genetically unstable offspring with an additional chromosome. The scientists took tissue from the cross for cell culture, eventually producing tens of thousands of plants. These were then subjected to an exhaustive search for those carrying the resistant gene on a wheat chromosome. Eight families were identified, which form the basis of the present crosses.
Intermediate wheat grass is proving to be something of a treasure chest. After discovering that the BYDV-resistant Hartog-like line QT8733 is resistant to the nematode Pratylenchus thornei, researchers are now testing it for resistance to the related species Pratylenchus neglectus. The two species of root lesion nematodes are responsible for yield losses of up to 40 per cent in susceptible wheat varieties.
Pratylenchus neglectus, most common in South Australia, is also emerging as a serious problem in NSW and Qld. Pratylenchus thornei is a recognised constraint to production in NSW and Qld.
It is known that the parent grass contains genes for resistance to stem, leaf and stripe rust. Researchers are back-crossing with the variety Janz to see if the there is a potential replacement for the Lr24 gene, which recently fell victim to a new rust pathotype.
BYDV is transmitted by aphids. At the South Australian Research and Development Institute, Hugh Wallwork says that two infestations are possible each year in April, May and again in August. “In most traditional wheat-growing areas the crop won’t be up when that autumn flight hits and so is safe from the disease but where you get very early sowings, as with the winter wheats, the disease can be very serious,” he says.
Internationally the disease is even more important. It’s considered the most serious viral disease of cereal crops in the world and is of particular importance in China, Europe and the USA. CIMMYT, the international centre for wheat breeding, has taken up the material as a high priority.
Contact: Dr Phil Banks 07 4639 8888 email email@example.com or Ms Susan Kleven 02 6246 5374 email firstname.lastname@example.org