New outbreak, but wheat virus fears could prove unfounded

A fourth outbreak of wheat streak mosaic virus, detected in research crops in Victoria today, has raised concerns that the virus may become a wider problem.

But the virus may not pose much of a risk to Australia's cereal crops after all, according to a leading plant scientist at Adelaide University and research director of the CRC for Molecular Plant Breeding.

The detection of the virus in Victoria follows outbreaks at Adelaide's Waite campus last week and another on Monday at Toowoomba in Queensland. At CSIRO Plant Industry, where the virus was first detected, 30,000 plants have now been destroyed to combat the virus, a cereal plant pathogen that causes widespread destruction of crops in the US and Europe.

But Prof Peter Langridge told Australian Biotechnology News that media reports claiming the virus could potentially damage up to 90 per cent of Australia's crops were unsubstantiated. In fact, he said, the virus had never even been considered a serious threat to Australia's grains industry.

"It's a bad time -- everyone is very nervous about viruses at the moment," Langridge said.

Langridge's own research programs are hanging in the balance, while the Adelaide outbreak is investigated. The quarantine that has been enforced by Plant Health Australia and South Australia's Department of Primary Industries means that not even nucleic acid can be sent out of the facilities for the time being. And the researchers, particularly the students among them, are worried about the possibility of having to destroy the plants they have spent months, if not years, developing.

Tragically for CSIRO, it may yet turn out that the virus has been in Australia for years, without causing major damage to Australia's cereal crops and breeding programs.

One Waite wheat breeder said similar symptoms had been present in wheat plants in Australia for more than 10 years.

New assays can detect virus

Langridge said that the difference now was that sensitive PCR-based assays had been developed that were capable of picking up the virus. "We have the assays now, so we can see it," he said.

Australia has a number of programs aimed at developing resistance to potential pathogens not yet found in Australia, according to Langridge. In general, these programs look at developing varieties with resistance genes to serious diseases, using molecular markers to select for the resistance genes. In this way, the plants do not even have to be exposed to the pathogen until relatively late in the game, and are usually sent overseas to be tested by breeding partners, thus avoiding the need to bring the infectious agent into Australia at all.

So far, the strategy has been a good one, and has worked for every pathogen that the plant geneticists have targeted. But the virus has never been seen as sufficiently important as a potential threat to Australian crops to justify an active breeding program to look at resistance, said Langridge. Instead, the focus has been on far more devastating diseases including stripe rust in barley, karnal bunt and the Russian wheat aphid.

"It's important to know that we have active breeding programs in Australia, breeding and selecting for resistance to exotic diseases. We have material in the pipeline that could be released to growers fairly quickly -- within one or two years," he said. "We've tried to pre-empt the major diseases, as you'd expect that at some time they'll be brought in. There's a lot going on that should help us."

Even if the virus becomes a serious threat to Australia's grain industry, Langridge said that new resistant cereal varieties could probably be developed within about five years.

Another strike against the virus, according to Langridge, is the difference in the growing environment between Australia and the countries which do have a problem with the virus, which includes the US and parts of Northern Europe. Factors involved include climate differences, as well as crop planting and rotation practices.

"The spectrum of diseases we face is very different to that in other parts of the world," he said.