The Justice Department announced charges on Tuesday against two Chinese researchers accused of trying to smuggle a fungus into the United States, bringing the case as the government pushes to keep more Chinese students out of the country.

       The students, Yunqing Jian, 33, and Zunyong Liu, 34, were in a romantic relationship last July, when U.S. authorities say Mr. Liu arrived in the country carrying small bags of the fungus Fusarium graminearum, which causes a disease that can cripple wheat, barley, maize and rice.

       The disease, head blight, is a familiar problem for American farmers, particularly in Northern and Eastern states, according to research funded by the Agriculture Department that has tracked it in 32 states last year. The fungus can be particularly damaging to winter wheat crops.

       Ms. Jian was arrested and booked in the federal courthouse in Detroit; Mr. Liu is believed to be in China. The criminal charges come as tensions mount between the United States and China over the Trump administration’s vow to “aggressively” revoke student visas for Chinese nationals. Such students, the administration says, risk siphoning off sensitive technology or trade secrets from American labs for the benefit of their home country.

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       Jerome F. Gorgon Jr., the interim U.S. attorney in Detroit, said the researchers’ actions amounted to “the gravest national security concerns,” saying they had tried to bring “a potential agroterrorism weapon” into “the heartland of America.”

       For decades, U.S. national security officials have worried about — and sometimes arrested — Chinese academics suspected of stealing scientific data from American universities and businesses. The Trump administration’s new push goes further by stripping an unspecified number of students of visas.

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