A Chinese scientist entered the U.S. last year with a toxic fungus stashed in his backpack, federal authorities said Tuesday as they filed charges against him and a girlfriend who worked in a lab at the University of Michigan.

The pathogen is known as Fusarium graminearum, which can attack wheat, barley, maize and rice and sicken livestock and people, the FBI said in a court filing in Detroit.

The FBI said a scientific journal describes it as a “potential agroterrorism weapon.”

Yunqing Jian, 33, and Zunyong Liu, 34, were charged with conspiracy, smuggling, making false statements and visa fraud.

“The alleged actions of these Chinese nationals, including a loyal member of the Chinese Communist Party, are of the gravest national security concerns," U.S. Attorney Jerome Gorgon Jr. said.

Exercise significantly improves survival for Colon cancer patients: Study

Jian appeared in court and was returned to jail to await a bond hearing Thursday. An attorney who was assigned only for her initial appearance declined to comment.

In July 2024, Liu was turned away at the Detroit airport and sent back to China after changing his story during an interrogation about red plant material discovered in his backpack, the FBI said.

He initially claimed ignorance about the samples but later said he was planning to use the material for research at a University of Michigan lab where Jian worked and where Liu previously worked, the FBI said.

The FBI said authorities found a scientific article on Liu's phone that was titled, "Plant-Pathogen Warfare under Changing Climate Conditions."

A week before arriving in the U.S., according to investigators, Liu exchanged messages with Jian, who said, “It’s a pity that I still have to work for you.”

The FBI said Liu replied: “Once this is done, everything else will be easy.”

Months later, in February, FBI agents visited Jian at the campus lab. She said, “100% no,” when asked if she had been assisting Liu with the pathogen at the lab. The FBI said it found a signed statement on her phone expressing her support for the Communist Party of China.

Messages between the two in 2024 suggest that Jian was already tending to Fusarium graminearum at the campus lab before Liu was caught at the Detroit airport, the FBI said. The university does not have federal permits to handle it.

FDA approves Moderna's new lower-dose COVID-19 vaccine

The U.S. does not have an extradition treaty with China, which makes Liu's arrest unlikely unless he returns.