Silvio Berlusconi's conservative government was split last night on the issue of genetically modified crops, and farmers warned that delays in agreeing rules could lead to next year's Italian harvests being unintentionally "contaminated".

The dispute has cut across traditional loyalties, pushing growers, environmentalists, leftwingers and nationalist-minded "post-fascists" into an unlikely alliance. Opinion among farmers and the public is overwhelmingly opposed to the introduction of GM seeds.

But at the weekend Mr Berlusconi personally scotched an attempt by his agriculture minister to impose stringent restrictions on the cultivation of GM crops. Last month, the European Union added the first genetically modified strains to its common seed catalogue, opening the way for farmers throughout the continent to plant them.

The agriculture minister, Giovanni Alemanno, a member of the post-fascist National Alliance, responded by drawing up an emergency decree laying down guidelines for the planting of GM crops.

After the cabinet broke up last week without an agreement on Mr Alemanno's proposed order, the prime minister doomed the measure by publicly branding it "illiberal". The agriculture minister declared that "if it proves impossible to get it through cabinet we shall have to find other ways".

Mr Berlusconi's Forza Italia party espouses the same free trade principles invoked by the US and Canada in support of genetically modified agriculture. But the prime minister's stance has also prompted criticism from within his own party. The Forza Italia governor of Piedmont, Enzo Ghigo, said: "We feel the exercise of liberty is in allowing producers and consumers to decide what they wish to grow and eat."