CSIRO reeling after wheat virus outbreak

It's a nightmare scenario -- scientists forced to destroy months, even years of their labour to combat an outbreak of a virus never seen in Australia. And it has just happened at CSIRO Plant Industry, where thousands of plants have recently been destroyed to combat the wheat streak mosaic virus (WSMV), a cereal plant pathogen that has never before been identified in Australia.

And a second outbreak, announced at Adelaide's Waite campus this week, has raised concerns that the virus may become a wider problem. A national surveillance and sampling program has been instigated by the Consultative Committee on Exotic Plant Pest Diseases to investigate the outbreaks and monitor for the virus.

The nightmare began with the observation over the summer that wheat plants in the organisation's greenhouses looked a bit streaky, said Plant Industry deputy chief Dr TJ Higgins. "It was clearly a disease of some kind... but we didn't initially quarantine the plants as their condition could have been due to stress," he said.

According to Higgins, greenhouse plants normally look a bit stressed, as a result of being grown in small pots. But to be on the safe side, the researchers started looking for the cause.

Samples from the sick plants were sent over to a commercial plant testing lab in the US, where they were tested for eight different plant viruses, including WSMV. The results of the antibody tests all came back negative.

By this time, Higgins said, CSIRO researchers were pretty sure they were dealing with a pathogenic virus and WSMV was at the top of the list. So they set about coming up with their own test. "CSIRO set up a PCR test for the most likely candidate -- wheat streak mosaic virus -- and it came back positive," he said.

The damning result, obtained on April 3, came as a complete shock to the division. WSMV had never before been seen in Australia, although it is a common disease in the US and other countries and is spread by the wheat curl mite, a microscopic mite endemic across Australia.

It also raised questions about the negative results from the commercial testing laboratory. While Higgins said that strain differences could have been responsible, the strain identified in Australia did not appear to be significantly different.

"The company did not give back entirely satisfactory reasons for the negative results," said Higgins.

In the meantime CSIRO had already called in Plant Health Australia, responsible for coordinating plant health issues, and quarantined all of the sick plants, destroying most of the diseased material. But with the identification of a quarantinable disease, CSIRO set about destroying all of the plants that could act as a host for the virus, including wheat, barley, oats, maize and other cereal plants, at its Black Mountain and Ginninderra facilities.

In addition to the plants being grown by CSIRO researchers, native grasses around the greenhouses were destroyed and an intensive greenhouse sterilising program put into place. Seed material sent to 18 locations around Australia was also destroyed, and plants in those locations tested to ensure they hadn't been infected.

In all, more than 30,000 plants were destroyed by the researchers, setting back CSIRO's cereal research programs by months, and in some cases several years. "It has been very sobering, to say the least," said Higgins.

Program savaged

"It has affected our group very savagely," agreed Dr Richard Richards, leader of the High Performance Crops for Australia program, which was in the process of commercialising a number of important new varieties including one resistant to a far more devastating pathogen, the barley yellow dwarf virus.

Richards said the devastating outcome had caused a great deal of uncertainty at CSIRO, especially among researchers on short-term appointments like postdocs and students. But he said the enforced hiatus from research meant scientists and technicians at CSIRO were catching up with analysing results and writing papers, and taking the opportunity to pick up skills from other areas.

"It gives people a chance to take stock of where we are and reassess priorities," Richards said. "And we're looking at the most efficient and creative ways of moving forward."

Last week, however, the South Australian government announced that WSMV had been identified in plants at the Waite agricultural precinct, home to a number of organisations including the South Australian Research and Development Institute (SARDI) and University of Adelaide researchers.

The campus has been put under quarantine while the outbreak is investigated. But for now it doesn't appear that the two outbreaks are connected. Plants originating at CSIRO in Canberra, which have been quarantined, have tested negative for the virus.

"There is no evidence that this [infection] is related to the recent CSIRO infection at this point," said David Cartwright, the chief inspector of plant health for South Australia's Department of Primary Industries.

Virus samples from the Waite outbreak have been sent to CSIRO for further testing and sequencing, with results expected in a couple of weeks time.

Source a mystery

One of the big mysteries of the outbreak is how it got into the country. Australia is free from many plant diseases, especially viruses, and has stringent quarantine procedures to ensure it stays that way.

"The mite has been present in Australia for a very long time, but we don't know where the virus came from," Higgins said. He said the virus was not readily transmitted by seeds -- the only plant material allowed in by the Australian Quarantine and Inspection Service, and the while there is a remote chance that the virus was carried in on someone's clothing, it is extremely small, as neither the virus nor the mite survive in the absence of plant material for long.

But perhaps the virus has been present but unaccounted for in Australia to date. "We can't dismiss the possibility that it occurs at a very low level out there," said Richards. He said the fact that it had shown up at the Waite campus, seemingly independent of the CSIRO outbreak, suggested that it might have been due to an unusual confluence of circumstances.

In any case, Higgins said, it was difficult to know what more could have been done. "The quarantine service works very well but it is hard to manage that residual risk. Surveillance is still the best possibility," he said. "And this virus doesn't show symptoms easily, they only appear when the plant is stressed."