Lincoln, New Zealand
September 11, 2002

The New Zealand Institute for Crop and Food Research has developed potatoes with proven resistance to the potato tuber moth, the major pest for the country's NZ$84-million industry. In a parallel development they have also developed potatoes with resistance to bacterial soft rot. Program leader, Dr Tony Conner is well known for his pioneer work in the genetic modification of potatoes.

Traditional breeding techniques are limited by a lack of appropriate germplasm for resistance to tuber moth and current control measures often rely heavily on pesticides. There are no known sources of resistance to bacterial soft rot within potato germplasm.

The tuber moth resistant plants contain 'cry' genes from Bacillus thuringiensis or Bt, a well-established genetic modification technique and the bacterial soft rot resistance is conferred by a synthetic magainin gene.

GM crops are controversial in New Zealand which has a moratorium on commercial production in place until October 2003. The GM trials have been conducted under stringent conditions for the last 5 years.

Tubers for the trials have been produced in a containment greenhouse and are then hardened off before planting in the field. The field trial is contained by a buffer zone of three rows of non-transgenic potato plants, as well as an isolation distance of at least 50 yards from other non-modified potato crops.

Subsequent monitoring of the trial site for 1-2 years after harvest, coupled with the immediate removal of any potato plants, aims to ensure complete elimination of genetically engineered potato plants from the trial site.

The trials have shown that Dr Conner and his colleagues have been able to develop potatoes with a high level of resistance to potato tuber moth in the field. In larger-scale field trials during the 2000-2001 summer, a high infestation was seen in the non-GM parental lines, but not the four high-performing GM lines.

GM Russet Burbank and Red Rascal lines had less than 0.2% of tubers with potato tuber moth 'mines', while 25% of the tubers in the control sample were affected. The GM lines showed no reduction in yield compared to the control lines.

The magainin gene was expressed at various levels showing various degrees of resistance to bacterial soft rot. The two best lines showed significantly better resistance to soft rot when tested against a "massive" dose of Erwinia cells, the causal agent. Dr Conner believes that the gene may also confer good field resistance to other bacterial and fungal diseases.

The potential benefits of the tuber moth resistant potatoes are reduced pesticide requirements as well as reduced pesticide residues in soils and ground water. The bacterial soft rot resistance will be of direct benefit to consumers who are occasionally horrified at putting their hand in to a bag of potatoes and finding a slimy, smelly mess.

Dr Conner plans to undertake wider regional testing of GM potato cultivars in the near future.