A rumour spread by text message has badly hit the price of bananas from China's Hainan island, state media say.
The messages claim the fruit contains viruses similar to Sars, the severe respiratory illness which has killed hundreds of people worldwide.
Producers in Hainan say the resulting price slump is costing them up to 20 million yuan ($US2.6m) a day.
China's Agriculture Ministry has dismissed the Sars claim as baseless. Police are investigating its source.
"It is utterly a rumour," a Chinese Health Ministry official was quoted as saying by Xinhua news agency.
"There has not been a case in the world in which humans have contracted a plant virus, and there is not any scientific evidence."
Hainan bananas had already been subject to rumours they caused cancer, after the banana plantations were hit by blight earlier this year.
The banana fears come amid international concerns over tainted Chinese exports, including allegations of poisons in pet food and toothpaste.
The state-owned China Daily newspaper recently criticised China's food safety regulators and called on the government to do more to protect Chinese consumers.