The report says both AstraZeneca and Novartis have been accused in the past of working on GM crops which would force farmers into a continuing dependence on the companies' products.
Four groups concerned at the potential impact of genetically-modified (GM) plants say a planned new company will threaten farmers in developing countries.
They believe Syngenta, to be formed by a merger of AstraZeneca and Novartis, could make it impossible for farmers to save seeds from one year to the next.
The groups also suspect Syngenta may develop new GM technologies which would make farmers dependent on it in other ways. They want the new company to promise not to put farmers at risk in the ways they fear.
But Syngenta's chief executive officer designate, Michael Pragnell, accuses the groups of misunderstanding and misrepresenting the new company's GM policies.
Dependence
The four groups are the British development agency ActionAid, GeneWatch UK, the Berne Declaration, based in Switzerland, and the Swedish Society for Nature Conservation.
In a report, Syngenta: Switching off farmers' rights?, they say Syngenta will be "the world's largest agribusiness".
The report says both AstraZeneca and Novartis have been accused in the past of working on GM crops which would force farmers into a continuing dependence on the companies' products.
"The most famous are 'terminator seeds' - seeds modified to grow plants which produce infertile seed.
"Farmers have always saved seed, and 1.4 billion people still rely on them as their primary seed source.
"'Terminator' means farmers would have to buy new (patented) seed or chemicals which will switch off the sterility each year."
The report says "terminator" seeds are just one example of a range of GM techniques known as "genetic use restriction technologies" (Gurts).
These work by controlling the traits of GM crops with the application of special chemicals: because the plants' natural traits are said to have been betrayed, the techniques have been called "traitor technology".
Disregarded
The report acknowledges that both AstraZeneca and Novartis promised publicly not to commercialise the terminator patents they owned.
But it says both companies "have broken commitments" not to develop the technology.
The authors say: "Investigations in this report show that research and development around terminator and traitor seeds has continued since those promises were made.
"We have uncovered 11 new patents held by both companies which allow for genetic modification of staple crops which will:
The four groups are asking the new company to promise not to develop any crops using terminator technology, and not to conduct traitor technology field trials until the results of assessments of its impact are available.
They want governments to agree a global ban on terminator plants, and say Syngenta should promise not to develop plants with weakened disease resistance, or where saving seeds would depend on the use of a chemical.
Premature
But the accusations levelled at Syngenta have been rejected as ill-informed by the new company's chief executive officer designate, Michael Pragnell.
"The latest analysis of patents conducted by ActionAid is flawed because it misinterprets the application of the technology and its potential benefit," he said.
"Both Zeneca Agrochemicals and Novartis have reaffirmed their commitment not to introduce any technology in developing countries where seed germination is prevented.
"Syngenta believes that the responsible research and development of new crop technologies, and their application through sustainable agriculture and integrated crop management practices, will ultimately be of immense benefit to agriculture in the third world.
Mr Pragnell said GM seeds would account for just 2% of Syngenta's proforma sales in 1999.
"Syngenta recognises that there is currently some public concern, notably in Europe, about the use of new crop technologies," he said. "This is expressed through a number of groups including political parties, consumer organisations, campaigning bodies and some government organisations.
"Syngenta intends to be a participant in the public debate. However, all those who participate in this public debate have a responsibility not to misrepresent."