Next Generation Potato Varieties – the fight against blight.

Fighting blight: what does it take to bring a resistant variety to market?

Bringing new potato varieties to the marketplace is very much a combined effort with seed breeders working closely with growers to develop desirable agronomic traits, and the wider supply chain for those crucial characteristics such dry matter distribution, sugar formation and storability, for example. In parallel, the work of researchers across the globe informs the breeders about the moving target that is blight and puts potential new varieties through their paces in the field.

The James Hutton Institute is one such research body and currently has projects covering everything from pathogen diversity, evolution and phenotyping to host resistance and IPM. The knowledge gleaned from these projects, together with in-house research, inform the work of seed breeders like Agrico who has around 220,000 potato varieties starting 10 years of trials each year. And this is before growers, like Nick Taylor, start on-farm commercial trials.

Dr David Cooke, research leader in cell and molecular sciences at the James Hutton Institute is involved in strengthening the industry’s understanding of pathogen populations and how to best use inherent resistance to control late blight in the field as part of an IPM strategy.

“Varietal resistance doesn’t play as big a part in crop protection programmes as it really should,” he says. “It’s a form of protection that lasts; from the seed tubers right through to harvest and beyond.

“We are so reliant on fungicides yet pressure to reduce these inputs is mounting, not least from the pathogen itself. Late blight’s ability to reproduce both sexually and asexually means there’s tremendous variability within the population and it’s that variability that gives the pathogen it’s potential to resist fungicide activity – as we saw back in 2005 with the 37_A2 lineage and fluazinam.”

Know your enemy

It is why his work within the Euroblight project is so important. In 2020, 90 UK growers (FAB scouts) submitted nearly 700 genetic samples of late blight to the team at the James Hutton Institute for analysis. Together with samples gathered across the continent, researchers are able to track the evolution, spread and population growth of different genotypes. Work by Dr Cooke’s counterparts such as Dr Allison Lees are able to use the samples to determine sensitivity to active ingredients, as well as the pathogen’s mechanisms to overcome genetic resistance.

“Late blight, or phytophthora infestans, is not a fungus. It’s an oomcyte and can reproduce in two ways.

“Firstly the sexual cycle. This is where the hyphae of both mating types, A1 and A2 meet in a leaf. It triggers the production of oospores and gives new variation within the pathogen population.

“That is important in many parts of Europe, but not all. Within most of the U. K. for example, we tend to see more clonal lineages; a result of asexual reproduction. A very well adapted strain that has some advantageous trait, such as an ability to infect earlier for example, becomes dominant. That dominance often doesn’t last as long as those from sexual reproduction as rapid asexual reproduction accumulates deleterious mutations.

“It’s why we’re doing a lot of work on the sexual variables within populations, trying to predict which ones are going to be the winners, and which ones are going to be the losers.”

One of the more recent observations is the tendency for clones to be triploid, rather than diploid. “Like hybrid vigour in vegetable seeds, with three copies of every gene these clones are arguably better able to survive some of those deleterious mutations. We don’t fully understand how that works yet but many of these clones do seem to be surviving longer.”

Developing defences

While Dr Cooke and others at the James Hutton Institute are learning more about the pathogen’s genetic evolution in near real-time, Sjefke Allefs, director of Agrico Research, and his team are delving into the genetics of potatoes.

“All the cultivated potatoes originate from Peru,” explains Mr Allefs. “It was the Inca people that domesticated the first potatoes over 9,000 years ago. As the potato spread across the Andes, it met with the pathogen we now know as late blight, which originates from Mexico.

“And this is where we predominantly find wild varieties with high levels of genetic resistance. It is the main source of genes for our breeding programmes though we also draw from primitive and old varieties.”

Mr Allefs and his team use DNA markers to identify genes and the biological characteristics they invoke.

“We are heading for varieties that have accumulated combinations of R genes and R genes that have synergistic effects. My view is that, over time, we will be able to introduce varieties that, in principal, can still be attacked by the late blight fungus but the economic damage is considerably lower.”

Today Agrico offers a portfolio of nine ‘Next Generation’ varieties. All offer outstanding blight resistance. “Our Next Generation varieties contain different ‘new’ R genes. It takes longer than the usual 11 years to bring to market because we first have to dilute the wild gene, before integrating it with the breeding programme – we call this pre-breeding or integration breeding.”

Those 11 years are spent selecting and trialling the resulting varieties.

“From the gene pool we select parents which, by combination, we hope will give offspring clones that meet the market demands and then we make crosses – about 500 each year.”

At the glasshouse stage, the Agrico Group has over 220,000 offspring clones. “These are all unique individuals that have inherited characteristics from their parents. Each one is potentially a new variety but it will take a further nine consecutive years of field trials to find those that meet the demands of any market segments. On average, only 3-4 new varieties will make it to market each year.”

Putting a price on this work is difficult. But by dividing the R&D budget by the number of new varieties the company brings to market, Mr Allefs gives an indication that it costs about €1 million.

“There is, of course, no guarantee that if you spend this money you will have a marketable variety at the end of the decade,” he notes.

The work for the seed breeder doesn’t stop here. Once a new variety is found it needs to be multiplied for sale and heavily supported during its early years in the marketplace.

Agronomy for profit

Nick Taylor, with 150-200ha of potatoes on his 1,000ha farm in Shropshire is the largest organic vegetable grower in the country, and he is passionate about the potential of new varieties.

“Customer requirements are getting higher and higher. Any visible damage caused by pests and diseases is not acceptable anymore. So we’ve got to come up with solutions and variety choice is a huge part of that,” he says.

“They have always been varieties out there that can side-step these issues, the problem has been that they aren’t palatable or aesthetically pleasing to consumers.”

Mr Taylor has been running trials professionally, with Produce Solutions, for the last 5 years.

“We tend to grow new varieties in very small plots first. In the second year we’ll do a bigger plot trial before taking it to a field scale trial in the third year. It’s about ensuring the varieties are robust, understanding how they perform in our specific field conditions and developing the agronomic knowledge to optimise marketable yield.”

Last year Mr Taylor ran field-scale trials with two of Agrico’s ‘Next Generation’ varieties, Twinner and Twister.

“We grew 1 ha of each and they are proving to be very promising. Externally and internally they look really good, which is so important for the retail market. We just need to learn a little more about Twinner and its nitrogen requirements. It’s a very quick-growing variety and knowing how to best manage that to get optimum yields is something we’re still working on. But it looks beautiful. It’s shape, it’s skin-finish, it’s quality and it’s resistance to blight come together to make it a very exciting variety.”

Not all variety trials are a success and when they fail it is costly, as Mr Taylor recalls: “The investments are big and the risks are also big. Last year for example, we trialled a variety that has done very well in France. We put over 10ha in the ground and the internal damage from pests meant the whole crop was unsaleable. We didn’t sell a single spud and with costs ranging from £5,000-10,000 per hectare, it was an expensive trial.”

Calculating the cost

While it may be both expensive and time consuming to bring new, blight-resistant varieties to market there are multiple benefits.

For conventional growers the cost-savings can be significant. Agrico, in combination with partners in the Netherlands is exploring how best to exploit the resulting characteristics with conventional farmers. “We’ve had three growing seasons of experimental work with these varieties in conventional conditions,” explains Mr Allefs. “We’re proving conventional farmers, supported by decision-making tools, can save 3 – 7 blight sprays per crop. Where conditions are hotter and drier, the most sprays can be saved.

“With potentially resistance-breaking isolates tending to emerge later in the season, continuing with late-season fungicide applications help to protect and preserve the biology.”

At The James Hutton Institute Dr Cooke is exploring how host resistance can optimise IPM strategies. “We acknowledge that we’re not replacing fungicides anytime soon but what we want to do is use resistance and fungicides together to protect one another,” says Dr Cooke.