Everybody needs wild relatives

Aphanomyces in the pea on the right has diminished the roots significantly compared to the healthy ones to its left. To the left of the healthy roots, fusarium solani has done a great deal of damage. To the left of those, fusarium avenaceum has also caused problems.  |  Mike Raine photo

Plant breeders can’t always find the disease resistance in tame populations, so they look further afield

Wild relatives of agricultural crops have powerful genes that crop researchers can use to help cultivated varieties adapt to an ever-changing environment.

Kirstin Bett, of the College of Agriculture and Bioresources at the University of Saskatchewan, said disease resistance is a useful trait common in wild relatives of domestic crops that researchers might be able to better use.

“Disease resistance is a really good example of a trait that you’re more likely to find in a wild population than you will within the domesticated species, because the plants have been exposed over millennia to these pathogens and they survive in the wild,” she said.

Bett specializes in pulse crop genomics and dry bean breeding. She said crop breeders typically do not want to cross with wild species because those plants often come with a lot of genetic baggage that can take a long time for breeding programs to clean up.

But there are instances where researchers cannot find the genetic variability needed in cultivated species, so the next best thing is to go looking at close wild relatives of the crops.

This is especially the case with crops where researchers and breeders cannot use genetic modification technology to improve them, including pulses like peas and lentils.

When a production problem arises with modern pea and lentil varieties, there is a chance their wild relatives will be used to patch the hole.

Peas and lentils both have been hit hard by aphanomyces root rot on the Prairies.

This fungus was first found in Saskatchewan in 2012, but it quickly swept through the region and there are now fields that can no longer grow peas or lentils because aphanomyces would cause a complete crop failure.

“It’s (aphanomyces) by far the top issue facing growers across the province,” said Dave Greenshields, director of research and development at the Saskatchewan Pulse Growers.

“It’s going to be a lasting problem. I think if you look around at places that have historically grown peas, you know, it paints a pretty stark picture. So, you look at some of the northern states like Michigan or Wisconsin, used to grow peas don’t any more. France is another good example. Where they used to grow a lot of peas and they grow a lot less now, and that’s because of root diseases.”

There are no fungicides or seed treatments available to farmers that can prevent or stop aphanomyces.

So the pressure is mounting on crop researchers to find tolerance to this disease in either the land races or wild relatives of these crops, and then breed these traits into modern varieties.

Some tolerance has been found in pea varieties grown in other parts of the world, and Canadian farmers should soon be able to grow pea varieties that have aphanomyces tolerance.

For lentils, researchers have not been able to find resistance to this fungus in their surveys of lentil varieties from around the globe, so they are looking to the crop’s wild relatives for resistance or tolerance.

A recent study titled Crop Wild Relatives of the United States Require Urgent Conservation Action found wild relatives are under threat in the country, and that more needs to be done to protect these species.

The study was published by the Proceedings of the National Academy of Science of The United States of America (PNAS) in December, 2020, and it provides conservation assessments for 600 U.S. native plants that are wild relatives of important agricultural crops.

“We found that more than one-half of the species may be endangered in their natural habitats, and that the great majority require further conservation action,” the study said.

Habitat destruction, climate change, pollution, invasive species, and overharvesting in their natural habitats were all cited as reasons these wild relatives are in trouble.

In Canada, efforts are being made to collect and categorize wild relatives including by DivSeek International, which is housed in the Global Institute for Food Security in Saskatoon.

DivSeek is a not-for-profit organization that was founded in 2014 and its program director, Katy Navabi, said its goal is to unlock the potential of crop diversity to enhance the productivity, sustainability and resilience of crops.

“It (DivSeek) brings a community of scientists together from around the world to help characterize and utilize the gene the germplasm that is being conserved in the gene banks, and help bring them into breeding programs and to the fields of the farmers,” Navabi said.

She said access to genetic diversity is fundamental for crop breeders to make genetic gains when developing new cultivated lines.

“Creating genetic diversity and introducing wild relatives are important and challenging. It is important because not only do they help introduce new sources of novel genetic and exotic sources of genetics, but also because the wild relatives are resilient. They carry very interesting traits, like disease-resistant traits, they adapt to a lot of harsh climates,” Navabi said.

“The way I like to look at the wild relatives is that they are the treasure box of the breeders, but they need to know what it is in that treasure box. So characterizing them for specific traits or specific genes will make it easier for them to be utilized.”

Plant Gene Resources of Canada is Canada’s national Seed Genebank that’s managed by Ag Canada in a Saskatoon facility.

This Seed Genebank has about 112,000 items that are available for plant researchers to help them enhance crops grown in Canada.

Bett said the Seed Genebank is important for new crop development and for preserving genetic diversity, but that it’s a huge undertaking, hard to maintain, and underfunded.

“They (Seed Genebank) characterize the material every few years. You have to regrow the seed or the viability goes off. So whenever they regrow them they take notes on things like size, shape, colour, height, days to maturity, all those kind of basic traits and that’s all stored in a database,” Bett said.

“Then if I’m looking for something in particular, I can go into the database and say ‘hey, I want to see all your beans that have white seed coats’ or something like that, and then they’ll give you a whole list and you can pick which ones you want.”

She said the plant breeder’s equation basically says if you want genetic gain you to have genetic variability.

“You can make small incremental gains by crossing elite by elite. So you’re crossing your best material with your second best material and you can make gains,” Bett said.

“But at some point you’re going to run out of genetic variability and you’re going to need to inject more or you’re going to stagnate in the program and the improvements will be lesser and lesser over time.”

Beyond wild relatives, gene banks also keep domesticated material in their giant freezers that come from old land races. These are crops people have grown for generations that have been selected by farmers because they grow well in their region.

Bett said a concern with gene banks is they can become museums that have a one-way street with genetic material going in, but it doesn’t come out to be used in new crop varieties.

“Funders are reluctant to fund museums,” she said.

The PNAS study said further conservation action for U.S. native wild relatives is “clearly needed,” both to safeguard their diversity in gene banks and botanical gardens, and to facilitate their continued evolution in their natural habitats.

“Among the taxa assessed to be of urgent conservation priority are wild genetic resources of cereal, fibre, fruit, nut, oil, pulse, root and tuber, spice, sugar, and vegetable crops that collectively generate more than $116 billion in annual U.S. agricultural production value,” the study said in the discussion section.

Navabi said the clock is ticking to get these resources into gene banks before environmental pressures including climate changes wipes them out.

“We are not even doing enough in collecting and conserving them, and I’m not surprised because we don’t see a lot of genes being introduced from wild relatives in the new varieties that are being registered,” Navabi said.

Bett said getting genetic resources into seed banks can be difficult, requiring a pile of paperwork including approvals from the counties where you want to harvest wild relatives.

And some areas are just too dangerous for researchers to work in, including parts of the Middle East where many of the wild relatives of pulse crops live.

“War is not conducive to plants growing. Neither is human pressure on land use, and that’s also encroaching on a lot of these areas where there’s wild relatives growing,” Bett said.

“Once they disappear they’re not coming back, and so there’s sort of a push on these days to try and get into these regions (Middle East) before they all disappear.”

Because when a new disease emerges, or changes, Bett said the genetic resources in seed genebanks are essential.

“I always think of disease as a bit of a nuclear arms race, right. You’re just piling on more forms of tolerance or resistance, and then the pathogen can mutate and affect it. The reason the wilds are a source of these resistance genes tends to be because they’ve coexisted with these pathogens for so long,” Bett said.

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