Imported garlic a source of plant viruses
Doesn't go through seed stage which filters out viruses
Next time you plant the garlic that's sprouted in your kitchen cupboard you could be contributing to the spread of exotic viruses, say researchers.
So suggests a new study published in PLoS ONE.
"Garlic can have large numbers of viruses in it and that's exactly what we found," says plant virologist Dr Steve Wylie of Murdoch University in Perth, Australia.
Garlic is particularly susceptible to plant viruses because it propagates vegetatively and does not go through a seed stage.
"The seed has got a lot of mechanisms to filter out viruses so a lot of viruses don't actually make it through the seed and it's a way of a plant cleaning itself of viruses by going through a seed stage," says Wylie.
"Garlic doesn't have this luxury," he says. "And if you are a virus that is just a godsend."
Year after year, garlic accumulates viruses and Wylie and colleagues wondered what viruses might by hitching a ride on imported garlic.
International trade in fresh produce has been on the rise since the softening of trade barriers and the ever-popular garlic is no exception, says Wylie, adding that Australia imports 85 per cent of its garlic and in Canada, it's as much as 68 per cent.
"We're bringing in 3,500 tonnes of garlic a year, mostly from China."
Infected bulbs grow so much slower. They are smaller, the quality is lower and the grower gets a lower price.- Plant virologist Steve Wylie
Wylie and colleagues went to supermarkets and collected 11 bulbs of garlic including those from Australia, China, the U.S., Mexico, Argentina, Spain. They then used high-throughput sequencing technology as a means of detecting viruses in the bulbs.
"Every bulb had viruses," says Wylie.
He says they found 11 RNA viruses, including species from Mexico and Argentina that were "vastly different to anything that anybody in the world had ever seen before".
Wylie says while there are quarantine checks on garlic brought into Australia for farmers to grow, bulbs brought in for people to eat are not considered to be viable.
"But they are viable and people do pop them in the garden," he says, adding that gamma radiation treatment used to stop sprouting doesn't necessarily work.
He says once a clove of imported garlic infected with an exotic virus is planted this establishes the new virus in the country.
"Then an aphid or some sort of insect that can spread that virus can land on there, acquire the virus and then fly over the fence and infect something else."
While the plant viruses don't affect humans they can hit the local garlic industry, says Wylie.
"Infected bulbs grow so much slower. They are smaller, the quality is lower and the grower gets a lower price."
In addition, he says, native orchids can be infected by some of the viruses that infect garlic.
Wylie says the study has broader implications because exotic viruses could be brought in with imported potatoes and sweet potatoes and anything else that propagates vegetatively.
"I think it's a huge problem," he says.
He says viruses also accumulate on flower bulbs so imported daffodils, tulips and gladioli may also carry viruses not picked up by current checks.