Consumers, farmers squeezed as grain giants tighten grip
But consumers will feel the impact if importers and supermarkets are subject to higher prices, as the flexibility of supply reduces.
"There are efficiencies that are gained when you have this kind of consolidation. But, on the other hand, there's a danger in a situation where you have more and more controlled by fewer and fewer," he said.
"Ultimately this hurts the consumer. I don't know any time that you can concentrate so much leverage in so few hands that it doesn't eventually impact the consumer," Gaus added.
Gaus also saw the consolidation as a threat to producers who are faced with fewer potential buyers for their crops - meaning that they might be forced to accept lower prices for their produce.
Farmers are often dependent on the grain trading companies for their seed and fertilisers as well as providing a buyer for their crops.
"It (grain market consolidation) has a negative impact, both on the many producers that feed into this very small number of traders and on the other end on their customers and ultimately consumers," said Jodie Thorpe, policy adviser for Oxfam.
ADM, through the acquisition of GrainCorp, will join Cargill and Glencore, both of whom have already made major acquisitions in the world's second largest wheat exporter.
"If GrainCorp is swallowed up by U.S. giant Archer Daniels Midland, all bulk grain exporting capacity in South Australia, Victoria, NSW and Queensland will be foreign owned," said Warren Truss, leader of the opposition National Party.
"We are rapidly descending into a state where farmers will toil in their paddocks while post-farm gate profits from Australia's A$9 billion-a-year grain crops will be counted in multi-national boardrooms," he added.
Australia is a key exporter of wheat to China, where demand is expected to rise sharply in coming years.
"Such consolidation would result in lower prices for Australian farmers if those farmers are not big enough to compete," said Zhong Funing, director at the International Research Centre for Food and Agricultural Economics at Nanjing Agricultural University.
"China could also lose its access to relatively cheap Australian wheat. China's grain imports are definitely on the rise. There is limited scope for expanding the farmland while demand growth is coming largely from the livestock industry."