Weevil overcome, but GM pea project shelved

CSIRO Plant Industry in Canberra has wound up a decade-long project to develop a genetically modified field pea resistant to the destructive pea weevil, because poultry and pigs fed on the GM pea dropped about 10 per cent in productivity.

Project leader Dr TJ Higgins said the decision was based in economics -- while the pea is perfectly safe for livestock consumption, profit margins in the pig and poultry industries are so slender that they could not tolerate a 10 per cent productivity loss.

Higgins said the result was disappointing, because the GM pea met its primary objective of conferring complete protection against the destructive pea weevil, Bruchus pisorum. With the approval of the Office of the Gene Technology Regulator, its efficacy under field conditions was confirmed in small-scale field trials in Western Australia, South Australia, Victoria and NSW.

Unlike most weevils, which infest stored grain, the larvae of Bruchus pisorum infests living pea seeds. Higgins said the weevil was the second most important pest of the field-pea industry after the fungus disease black spot, Ascochyta blight.

The pest can be controlled with expensive pesticide sprays, which reduce profits, but Higgins said the bigger problem was that overseas customers will reject weevil-infested shipments.

His group obtained the protective transgene from a weevil-resistant Phaseolus bean. It encodes an alpha-amylase inhibitor, that binds to the active site of the alpha-amylase enzyme that allows the weevil to digest pea starch.

Higgins said decades of conventional plant breeding led to the loss of the field pea's own alpha-amylase-inhibitor gene, removing its protection against the pea weevil.

Early feeding trials in laboratory rats confirmed it was non-toxic, even at levels as high as 70 per cent of total dietary intake, and had no effect on food conversion efficiency. Unfortunately, later tests revealed a mild inhibitory effect on the alpha-amylase enzymes of pigs and chickens, that reduced their food conversion efficiency by around 10 per cent.

Farmers funded the project through the Grains Research Development Corporation, which has provided annual research grants of up to $150,000 each year for a decade.

Higgins said gene technology offered alternative approaches to the development of weevil-resistant peas. CSIRO researchers have subsequently identified other inhibitors of alpha-amylase enzymes in insects that have no effect on the equivalent mammalian digestive enzymes, but because there is no more funding, CSIRO has shelved the project.

But he said he believed the GRDC's $1.5 million had been well spent, because it would deliver substantial spin-off benefits in Australia and overseas, especially in developing nations.

To develop the GM pea, Higgins said, his team first needed to develop an efficient gene-transformation system that is potentially applicable to all legumes.

"We've also learned a great deal about gene expression in plants, especially the expression of transgenes in legumes," he said.

"If and when a resistance gene becomes available for black spot, the most serious pathogen of field peas and chickpeas, we will use our system to transform these crops.

"We've already used it to develop a weevil-resistant chickpea. I've just come back from India, where I've taught their molecular geneticists how to transform chickpea -- they're mad keen to use it to develop their own weevil-resistant chickpeas, because it's an important source of protein in southern Asia. We're also working to develop a weevil-resistant variety of cowpea, a staple crop in sub-Saharan Africa.

"The amylase inhibitor gene has no effect on humans, and both these crops are eaten exclusively by humans."

Higgins said it was "very feasible" to use the legume-transformation system to modify chickling vetch, another protein crop staple in southern Asia and Africa.

Chickling vetch contains a neurotoxic amino acid, and long-term consumption can paralyse the lower limbs. Minor genetic surgery to eliminate the toxic amino acid would render the crop safe to eat.

Higgins said the discovery that the GM field pea reduced feed-conversion efficiency in pigs and chickens demonstrated that Australia's system for regulating GM crop development, with its system of checks and balances throughout the life of transgenic crop projects, was working well.