A grain glut leaves some Eastern European countries caught between solidarity with Ukraine and survival.

After more than a year of surprisingly solid European unity in support of Ukraine, grains of discord are piling up in the barn of Robert Vieru, a Romanian farmer with 500 tons of wheat and 250 tons of sunflower seeds now sitting unsold because of cut-price Ukrainian competition.

A glut of Ukrainian cereals and other produce has nearly halved the value for the results of Mr. Vieru’s labors and left farmers across Eastern and Central Europe — and their governments, most of which face elections this year or next — caught between solidarity with Ukraine and their own survival.

“I feel sad for them but my heart breaks for myself,” Mr. Vieru said of Ukrainians living across the nearby border in Romania’s Danube River delta, as he opened the sliding door of a concrete barn, filled to the brim with last year’s unsold harvest.

Prices have been driven so low by a flood of cheap food from Ukraine, he said, that selling would mean earning less than he paid to produce his crops.

Mr. Vieru’s plight, shared by farmers in Poland, Hungary, Slovakia and Bulgaria, flow from the unintended consequences of good intentions gone awry.

Market forces, turbocharged by profiteering, have turned an ambitious effort by the European Union to help Ukraine export its harvest and ease what the United Nations described last year as an “unprecedented global hunger crisis” into a source of political division and economic distress in Europe’s formerly communist eastern lands.

The mess has not erased strong public support for Ukraine, at least not yet, but it has created an opening for far-right groups that favor Russia, generated serious frictions within the European bloc and soured moods in a region that had been a bastion of mostly unflagging support for Ukraine. A proposal from the European Commission of 100 million euros to compensate farmers has done little to assuage the tensions.

With the exception of Hungary, whose populist prime minister, Viktor Orban, has often cozied up to Russia, the countries hit hardest by the competition are among Ukraine’s most stalwart European allies. Poland, Romania and Slovakia have provided weapons and military training.

Over the past week, however, all five nations have imposed tight restrictions on importing Ukrainian grain, with only Romania stopping short of an outright ban.

“We are the last man standing,” Romania’s transport minister, Sorin Grindeanu, said in an interview.