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

Bringing new potato varieties to the marketplace is very much a combined effort. Seed breeders work closely with growers to develop desirable agronomic traits, and with the wider supply chain for those crucial characteristics such as dry matter distribution, sugar formation, and storability.

In parallel, the work of researchers across the globe informs breeders about blight and the genetic basis for varietal resistance.

The role of research

The James Hutton Institute in Scotland 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 which has around 220,000 potato varieties starting 10 years of trials each year. And this is before growers, like the UK’s 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.

David Cooke:
 

"Varietal resistance doesn't play as big a part in crop protection programs as it really should. 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 the 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 its potential to resist fungicide activity – as we saw back in 2017 with the 37_A2 lineage and fluazinam."

Know your enemy

It is why his work within the Fight Against Blight and Euroblight projects 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 can track the evolution, spread, and population growth of different genotypes.

Alison Lees:
 

"Late blight, or Phytophthora infestans, is not a fungus.  It’s an oomycete 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 generates 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 traits, such as an ability to infect earlier, for example, becomes dominant."

"That dominance often doesn’t last longer than 5-10 years as a clonal population has no way to rid itself of accumulating deleterious mutations. It’s why we’re doing a lot of work on the sexual variability 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 vigor 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 defenses

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.

Sjefke Allefs:
 

"All the cultivated potatoes originate from Peru. 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 programs 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.

Sjefke Allefs:
 

"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 principle, can still be attacked by the late blight fungus but the economic damage is considerably lower."

Agrico offers a portfolio of nine ‘Next Generation’ varieties. All offer outstanding blight resistance.

Sjefke Allefs:
 

"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 program – we call this pre-breeding or introgression breeding."

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

Sjefke Allefs:
 

"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 in the next season. 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 segment. 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 per variety.

Sjefke Allefs:
 

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

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, England, is the largest organic root vegetable grower in the UK and is passionate about the potential of new varieties.

Nick Taylor:
 

"Customer requirements are getting higher and higher.  Any visible damage pests and diseases cause is not acceptable anymore.  So we’ve got to come up with solutions and variety choice is a huge part of that."

"There 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.

Nick Taylor:
 

"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 optimize marketable yield."

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

Nick Taylor:
 

"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 shaped, it’s skin-finish, it’s quality and its 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.

Nick Taylor:
 

"The investments are big and the risks are also big.  Last year, for example, we trialed 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 GBP 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.

Sjefke Allefs:
 

"We’ve had three growing seasons of experimental work with these varieties in conventional conditions. We’re proving conventional farmers, supported by decision-making tools, can save 3–7 blight sprays per crop. Where conditions are hotter and drier, then most sprays can be saved."

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

At The James Hutton Institute, Dr. Cooke is exploring how host resistance can optimize IPM strategies.

David Cooke:
 

"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."