Blight-resistant Maris Piper at The Sainsbury Laboratory

16 April 2021

Image Caption

Photo was taken by Andrew Davis, John Innes Centre.

In 2016, field trials were approved to develop a Maris Piper potato that is better for consumers, farmers and our environment. Professor Jonathan Jones and Dr Agnieszka Witek tell us about the recent progress made on the “PiperPlus” potato in this ground-breaking Potato Partnership Project with Simplot and the start-up company, BioPotatoes.

What makes PiperPlus different from the original Maris Piper potato?

In this project, we have developed lines derived from the Maris Piper potato that are resistant to both late blight and tuber blight. Late blight is an ever-present potato disease that is controlled in northern Europe by 15-20 agrochemical sprays every year. Even with treatment, it can still cause severe losses. In addition, healthy tubers may be harvested from fields impacted by late blight, only to rot in storage due to tuber blight. With our new lines, potatoes are protected from blight in the field and during storage. Additional qualities have been developed in these lines to reduce losses during storage by decreasing bruising and the cold-induced accumulation of reducing sugars, such as glucose and fructose. These sugars along with the naturally occurring amino acid asparagine promote acrylamide formation and blackening when potatoes are cooked at high temperatures, such as in the frying or baking of crisps and chips. Acrylamide is toxic, so minimising the reducing sugar content is important when selecting varieties for foods cooked at high temperature.

In the header photo the two tubers on the right side were inoculated with a Phytophthora infestans (late blight) spore suspension, and the two on the left were mock-inoculated with sterile water as controls. The two tubers in the top row are from the genetically modified PiperPlus line 27 and the two in the bottom row are Maris Piper potatoes.

What are the new developments since your last field trial update in 2019?

Ten of our best lines were used in a field trial at the National Institute of Agricultural Botany (NIAB) in Cambridge in collaboration with Professor Gerard Bishop. The aim was to select the best lines of those ten and characterize them in more detail. We also wanted to test if there was a difference in yield between our lines and commercial Maris Piper. To make the results comparable, the tested potato plants were all treated with agrochemicals to prevent the late blight that would otherwise have decimated the Maris Piper. The yield of the best new lines was indistinguishable from Maris Piper. This showed that the process of making our resistant and tuber-quality improved lines did not compromise yield.

Potatoes, like many species in the Solanum genus, contain steroidal glycoalkaloids (SGAs) that can be toxic at high levels. Commercial Maris Piper potatoes contain low and safe levels of these toxins. We have now measured SGA levels in our new lines; they contain no more of these compounds than commercial Maris Piper.

To minimise the risk of forming acrylamide during cooking, having a potato that does not accumulate reducing sugars during cold storage is highly desirable. Our latest data show that after ten months of storage at 2 °C, the level of reducing sugars in our lines is a quarter of that seen in commercial Maris Piper. Our lines therefore bring significant benefits to consumers.

Our lines also show a reduction in the predisposition to bruising by more than half. An additional benefit of safe storing at low temperatures is the prevention of sprouting, which is another cause for heavy losses. Like with all potatoes, the sprouts of potatoes should not be consumed because they contain high levels of SGAs.

What do these changes mean for farmers and producers?

These new lines of Maris Piper could potentially save millions of pounds (~£450 per hectare) by removing the need to spray to control late blight. Reduced wastage of bruised, sprouting or cold-sweetened tubers after harvest will be an additional benefit. Potatoes need to be stored at temperatures below 3 °C to prevent sprouting and the spread of diseases. However, cold temperatures promote the unwanted production of the sugars. The chemical chlorpropham (CIPC) was used to suppress sprouting, but is no longer permitted for use in the EU due to its toxicity. Alternative sprout suppressants that are both effective and affordable have not yet been identified. Having a potato that can be stored at low temperatures without the need for chemical suppressants would also save money.

How could this benefit the general public?

These PiperPlus potatoes will require significantly less agrochemical input than Maris Piper or other varieties. Also, by reducing losses that usually arise from late blight, tuber blight and the deterioration of tubers, the overall yield per hectare of agricultural land will be much higher and post-harvest losses in storage will be reduced. The supply of these prized potatoes will therefore better meet demand and reduce the price in the shops.

Acrylamide is a chemical that is produced naturally in the cooking of many starchy foods, such as wheat or potatoes. Simplot’s InnateTM technology, which was used in the development of PiperPlus, can reduce the potential for the formation of acrylamide during cooking at high temperatures by up to 90%.

If our lines were approved for use in the UK, it would provide the opportunity for the UK to benefit from the investment that has been made from taxpayer-funded plant pathology research. As of now, it has only been adopted in the US.

What methods were used in developing this potato?

To confer blight resistance, we genetically modified the Maris Piper potato by transferring three blight resistance genes from close relatives of potato, one from Solanum venturii and two from Solanum americanum. To reduce bruising, cold-induced sweetening and the potential for forming acrylamide within the tubers we used Simplot’s Innate (TM) gene silencing technology that uses potato genes. This prevents the expression of polyphenol oxidase and invertase. These enzymes are involved in the formation of the dark coloured compounds in a bruise, and in the formation of glucose and fructose from sucrose, which combine with asparagine to form acrylamide at high temperatures.

Did you have any safety concerns when starting this field trial and how did you address them?

There are rigorous regulations governing the planting of GM crops in the UK. The Government’s independent group, ACRE (Advisory Committee on Releases to the Environment), assessed this application for potential environmental and health concerns in 2016 and strict measures were put in place before approval.

Environmental concerns relate to the unintended spread of the new lines to other plant populations (wild or agricultural). Our field trial plot is surrounded by a 3 m high fence so that animals cannot get in and facilitate the spreading of the plant, and the plants are at least 20 m away from any other potato crops. Furthermore, because potatoes are propagated as tubers, viable true seeds of cultivated potato plants usually don’t form or can be easily contained by removing the flowers or berries, meaning that distribution of genetic material that way is not a concern.

There is no scientific reason to anticipate that these modified potatoes could be unsafe to eat. Nevertheless, food safety testing will be undertaken before our lines will be permitted to be brought to market. Genetic modification is a very precise method, and the chance of it resulting in unintended consequences is very small, and no greater than the risk with accepted breeding methods. Many independent studies and years of consumption in other countries have shown that GM food is as safe to eat as conventionally produced food.

Who funded your research and who did you collaborate with?

The project is primarily funded by the Biotechnology and Biological Sciences Research Council (BBSRC) with additional funding from industry partners BioPotatoes (UK) and Simplot (US).

What are the chances of us seeing this blight-resistant potato in our supermarkets in the near future?

That depends on the outcome of the recent consultation on genetic technologies conducted by DEFRA. These potatoes are currently classified as GM, making them unlikely to ever reach the UK market, not least because of the high cost associated with the current regulations. Secretary of State, George Eustice, said in his address to the Oxford Farming Conference in January 2021, ” However, what we have learned since that initial GM debate is that cisgenesis – where traits are moved within a species or genus of plant – is also powerful, but raises far fewer ethical or biological concerns”. The resistance genes that we transferred to the PiperPlus potatoes are from species within the same genus, Solanum.

The adoption of a trait-based regulatory framework, rather than a technological one, would allow the benefits of each line to be assessed on a case-by-case basis. Once any changes to the UK regulations have been made, it might take 5 year for lines like ours to become available for producers and consumers. It would then be important to ensure that each crop is properly labelled to enable consumer choice. In the case of PiperPlus, for example, it would be the choice between one line that requires spraying with a lot of agrochemicals and another that requires far fewer agrochemical applications.