A patent dispute between the world's two biggest seed groups has escalated into a slanging match, with DuPont citing "fraud and inequitable conduct" by Monsanto, which taunted its rival for "commercial and scientific failures".

DuPont said it was trying to stamp out a "new anti-competitive campaign" by its larger rival by fighting for the right to blend Monsanto's so-called Roundup Ready genetically modified seed technology, which confers herbicide resistance, with its own.

Monsanto had obtained patent protection on Roundup Ready traits through illegal means, including lodging "knowingly false, incomplete and misleading" statements with authorities, the filing claimed.

And the company had "abused its unlawfully-acquired monopoly power" to block competition and impose price rises for the trait of 100% between 2004 and 2008.

"Competition in corn and soybean traits is at a critical crossroads, with farmers demanding, and advances in biotechnology making possible, the development of competing seed 'systems',"  DuPont said.

"Monsanto seeks not only to unlawfully preserve its existing trait monopolies, but to extend its monopoly power through exclusionary conduct into developing markets for stacked (combined) traits."

'Pirated' technology 

However, Monsanto, which last month began a legal fight to try to prevent DuPont selling seeds containing traits from both companies, dismissed the filing as a "smokescreen".

DuPont has admitted in January own herbicide resistant seed technology presented an "unacceptable risk" and required Roundup Ready to work.

"Rather than tell the truth about its failed product, DuPont pirated Monsanto's technology," Scott Partridge, Monsanto's deputy general counsel.

"DuPont wants to compete by hurling false accusations and using the innovations of others to cover up its own failed technologies.

"DuPont is trying to make up for its commercial and scientific failures by misusing Monsanto technology."