GM potato trials point to blight resistant crops of the future

The field trials follow successful lab experiments to modify Maris Piper potatoes with late blight resistance genes from wild relatives of potato called Solanum americanum and Solanum venturii.

To improve tuber quality, the modified Maris Piper lines also have genes switched off - or “silenced” - to reduce browning upon bruise damage and to avoid cold-induced sweetening (which is the accumulation of reducing sugars during cold storage that causes blackening when potatoes are cooked at high temperatures).

The Sainsbury Laboratory was granted permission earlier this year by DEFRA to proceed with three years of field trials in controlled conditions.

These trials in Norfolk this summer were set up to test if the genetic improvements were without side-effects for yield or lower performance in the field. They were funded by a BBSRC Super Follow-on Funding Grant.

“We have identified a plant that looks fine in terms of yield - comparable to wild type Maris Piper - but with all the benefits of blight resistance, reduced bruising and lower levels of reducing sugars,” says Professor Jonathan Jones of The Sainsbury Laboratory. “The really exciting thing about this trial is that our new line also shows resistance to tuber blight - the same pathogen that causes late blight can get into tubers and rot them. This will reduce losses in storage for potato growers.”

The next phase of trials funded by BBSRC, a part of UK Research and Innovation, will see 12 more lines go forward to more extensive yield trials before the final GM Maris Piper can be taken forward for regulatory assessment and commercialisation.

The Sainsbury Laboratory will collaborate with NIAB, Cambridge for further field evaluation of these new lines of potatoes.

UK farmers spend an estimated £60m a year on agrichemical applications to control potato late blight which if left unchecked can destroy a crop within two weeks.

By using natural genetic diversity found in the wider potato family and introducing it into modern potato cultivars, farmers would have to rely less on agrichemicals which are costly and cause environmental concern.

European regulations on GM crops are complex but with the UK’s future in relation to Europe still to be confirmed, the project will press ahead with further trials.

“The future regulatory framework is an imponderable,” says Professor Jones. “But we have shown that the technology works. These improvements were made in Maris Piper, the most planted UK potato variety. If you want to use our genetic knowledge to solve problems in the field, you need to do so in the most preferred variety.”

“I would urge people to support this technology, and not to create obstacles to using it to solve real problems in the field in a more environmentally sustainable way. We all want to see a more sustainable agriculture, and to achieve that goal, we need to replace chemistry with genetics for disease and pest control.”

The research has previously been funded by the BBSRC via a Horticulture and Potato Initiative (HAPI) grant, and is in partnership with Biopotatoes Ltd, UK and Simplot Plant Sciences in the USA.

Background information

• Late blight caused the Irish Potato famine of the 19th Century. It results from infection by the fungal-like mould Phytophthora infestans, causing losses of $6B/ year for potato and tomato production.
• Potato is the fourth most important crop in the world and widely grown in Europe, USA, South America, Canada, China, India and Africa.

How are potatoes genetically modified?

Potato is easy to modify using strains of nature’s genetic engineer the bacterium Agrobacterium tumefaciens which transfers specific genes into cells of potato. Pieces of potato stem are used for making the genetically modified potato plants.

Cells which have received the gene from the bacterium form a mass of undifferentiated cells, or callus, on the cut ends of the potato stem pieces. These transformed cells are encouraged using plant hormones to form new shoots and roots and after a few weeks become a genetically modified potato. Multiple such new plants are then evaluated to identify those that are the same as the original potato except they now contain the additional introduced gene (in this case the resistance to potato blight transferred from the wild relative).

Why is GM needed for late blight resistance, why not use traditional breeding?

Traditional breeding techniques have failed to produce varieties that have durable resistance to late blight. This is because they have tended to introduce resistance genes one at a time which are easily overcome by the pathogen.

Professor Jonathan Jones says: “If you put in three effective genes at once they are all in effect saving each other because a mutation that enables the pathogen to overcome one of them won't overcome the other two. I think that resistance in these lines should last for decades.”

Tuber quality traits: why is bruising an issue?

Bruising causes millions of potatoes to be thrown away every year. Maris Piper lines used in these trials have a gene switched off, or silenced, which makes the tuber less prone to bruising and ensure that the potato meets customer quality specifications.

“There is a lot of wastage from bruising. Potato harvest is in September/October so to ensure there is a product for consumers in April is tricky. This will make it much easier for this challenge to be addressed.”

Tuber quality trait: what is cold induced sweetening and how does it affect tuber quality?

The accumulation of reducing sugars such as glucose and fructose in potato during cold storage is a problem because it leads to browning and the formation of acrylamide when potatoes are cooked at high temperatures, for example when cooking crisps or chips. This process is known as cold-induced sweetening.

The Sainsbury Laboratory team has silenced a gene for an enzyme required for this sweetening, which leads to lower levels of reducing sugars when potatoes are stored at low temperatures (which are needed to prevent sprouting prior to sale).

“Our GM Maris Piper genotype means you would be able to store potatoes without chemical treatment at 2 degrees and they won’t have the cold-induced sweetening. This addresses a crucial problem for the industry,” says Professor Jones.