Using the canola at the University of Manitoba's greenhouse, professor Mark Belmonte and his colleagues are exploring ways to defend the plants from Sclerotinia sclerotiorum, a crop-destroying pest that's grown increasingly resistant to fungicides.
A leafspotting guide
How does white mould afflict canola so it can grow and spread? Learn more below about its life cycle.
Since canola first arrived in Canada decades ago, farmers have been embroiled in an arms race with a deadly fungus. They were frequently losing. But that might be about to change.
Canada’s canola crop has no natural defences against Sclerotinia sclerotiorum, also known as white mould. In hot and humid years – conditions in which the mould thrives – 89 per cent of Western Canada (where the majority of canola is grown) fields can be infected. The only defence is a smorgasbord of fungicides, to which the mould grows more resistant with each passing season. It is currently the biggest threat to a crop that contributes $29.9-billion to Canada’s economy.
“It is canola’s number 1 yield killer,” said Mark Belmonte, a researcher at the University of Manitoba. “The arch-nemesis.”
The fungus gets its Latin name from the dark, hardened beads, or sclerotia, that it forms to lay dormant in the soil. The Manitoba researchers have recreated some in Petri dishes.
However, canola has a new weapon coming.
Prof. Belmonte and a team of researchers at the University of Manitoba have developed an RNA that can infiltrate the body of the white mould, destroying it from within. It is easy to apply. It promises to be better for the environment. And it is targeted.
The technology is around five years from commercial application. It is part of a growing body that works on a genetic level – either through RNA or gene-editing – to control pests.
These tools are in acute demand as climate change transforms weather patterns and alters geographic boundaries, boosting the virulence of numerous pests, from fungi to insects.
Currently, up to 40 per cent of global crops are lost annually because of plant pests and disease, with that total expected to climb, according to the United Nations’ Food and Agriculture Organization.
These pests have also grown an immunity to more traditional chemical pesticides, while ecosystems have continued to suffer from pesticides, a leading cause of biodiversity loss, with recent reports noting steep declines in insect biomass, bird populations and pollinators.
However, any new pesticides developed in a lab, especially when it comes to food, invites questions about safety, and the effects on the broader ecosystem. Before introducing a new weapon to the agricultural arsenal, industry, researchers and consumers must consider the consequences, both known and unknown.
With canola leaves carefully laid out on wet paper towels, Prof. Belmonte shows how they are prepared to test foliar fungicides. The chemicals used to kill harmful fungi can end up killing helpful ones too.
Outside the lab building where Prof. Belmonte works, there is a bust of Baldur Rosmund Stefansson, the plant breeder who adapted rapeseed into the high-yield canola – short for 'Canadian oil' – that we know today.
Sclerotinia sclerotiorum takes no prisoners, especially when it comes to canola.
The mother ship is a mushroom-like stool that emerges from the soil in the spring. It releases millions of microscopic, feather-light spores that land on canola petals and leaves and infiltrate the plant’s vascular system, transforming into tiny black pebbles that clog the xylem and phloem. The suffocated plant rots and decays and the pebbles fall back into the soil, where they can lay dormant for 10 years, waiting for the next moment to strike.
Canola has no natural immunity to white mould, meaning that farmers have been unable to breed a truly resistant variety.
Traditionally, white mould is fought using fungicides. However, chemical fungicides destroy everything in their path, including beneficial fungus that play an essential role in the ecosystem and can be helpful to the canola plant. Fungicides are also proving to be less effective against white mould. In recent years, Sclerotinia has grown more resistant to these chemicals.
The cost of crop protection against fungicide each season is around $22 to $25 an acre, before application costs. This can increase the price by another $10 to $13, depending on whether a plane is required, said Roger Chevraux, a canola farmer southeast of Edmonton who has 2,000 acres of the crop. But to apply or not to apply is a guessing game, he said. Sclerotinia is stealthy. The fungi take hold at the start of the season, when the canola flowers bloom, but signs do not show until later.
“As a farmer we do everything we can to control what happens in our fields but some things – weather and disease – we cannot control,” he said.
Roger Chevraux’s family has farmed near Killam, Alta., since 1912. He has dealt with destructive white mould before.
A bad year in recent memory was 2016 when, according to estimates from the Canola Council of Canada, 89 per cent of canola fields surveyed in Western Canada were infected. The conditions were just right – hot, humid and the canopy was dense, creating a perfect, damp shelter for the white mould to thrive. The white mould is not totally destructive. Some plants survive, however, yield losses can reach 50 per cent.
To be safe, Mr. Chevraux treats at least some of his acres most years, with the amount depending on the conditions. If the weather is hot and humid he will treat more. In years where he needs to treat all 2,000 acres, costs could reach as high as $70,000. Less guessing and more certainty is what Prof. Belmonte is hoping to provide with his tool to fight Sclerotinia.
It all started with finding a RNA molecule that looked like those in the fungi that coded for certain proteins, the ones that allowed it to be toxic to canola.
RNA is a messenger that delivers information from DNA to eventually build proteins in a cell. Once they identified that RNA, they designed a double-stranded RNA look-alike. The look-alike is then sprayed onto the crop so that when the fungus arrives it is absorbed and processed in the pathogen. These double stranded RNAs that code for the toxic traits of Sclerotinia interfere with RNAs in the fungus, reducing the effect the disease on the crop. “We’re tricking the fungus into thinking that it’s consuming something that’s bad and then it’s essentially killing itself in different ways,” said Prof. Belmonte.
The success rates are similar to traditional broad spectrum fungicides, based on results so far.
The RNA molecule can be applied to canola fields through a spray application, much like a more traditional fungicide. Prof. Belmonte is also working to develop canola that can make the RNA molecule itself, essentially developing a crop with genetic resistance across the life cycle of the plant. This research is a little further out than the spray application.
In canola fields like Mr. Chevraux’s in Alberta, farmers must often guess which parts to spray with fungicide, depending on conditions. The researchers in Manitoba hope that spraying the RNA molecules, or developing crops that make the molecule themselves, will offer a better defence.
Currently, nothing exists in Canada for a fungicide that combats white mould by interfering with RNA and proteins. However, in the United States there is an RNA interference, or RNAi, fungicide that controls the Colorado Potato Beetle. Trials for more products – in Canada and the U.S. – continue.
However, the research fits into a growing body of work on cellular synthesis and gene-editing for the purposes of pest control. These tools vary. Mr. Belmonte’s technology uses RNA interference; other work uses a different technology to edit gene sequences. A prominent example is genetically modified mosquitoes, a tool against malaria and other insect-borne diseases. However, for the most part, few technologies are advanced enough to be involved in field trials, according to a Council of Canadian Academies report on the topic published in November.
But the technology is being picked up because of a major advantage: precision, says Robert Slater, the chair of an expert panel on the report published in November, an initiative of the Council of Canadian Academies.
For example, in the case of Prof. Belmonte’s RNAi, it is only harmful to Sclerotinia, not the other beneficial fungus in the area.
“It’s a pinpoint as opposed to a bludgeon,” said Mr. Slater.
The Council of Canadian Academies report said that gene-editing organisms for pest control have wide-ranging implications for controlling insect-borne disease, invasive species and to slow down the worrying trend of pesticide resistance, which is often growing faster than we can develop new pesticides, said Mr. Slater.
However, the report also found that the technology poses a number of risks, from environmental to social.
The environmental risks are because it’s a novel technology, said Mr. Slater. A gene-edited fungicide could, for example, have unknown effects on ecosystems. These new strategies for combatting pesticides therefore need to take precautions.
Prof. Belmonte is in field trials to see how the new technology fares outside the greenhouse.
For example, Prof. Belmonte’s lab has spent several years trialing the fungicide in a controlled greenhouse setting to ensure that the RNA molecule is specific to Sclerotinia and will not affect other fungi. They found that when applied to various other fungi it had no effect.
Prof. Belmonte is now in field trials, working with industry partners and the Canola Council of Canada to assess the impact that the new technology has on the surrounding ecosystem. They are also testing to see if the technology is durable and consistent in various geographical locations. A benefit of the technology – compared to traditional fungicides – is that the RNA molecule breaks down quickly within the environment.
“We have now the greatest type of information at our fingertips to be able to precisely engineer the plant with as much knowledge as possible,” said Prof. Belmonte.
Leafspotting: See how Sclerotinia grows and spreads
Sclerotinia stem rot is one of the most economically significant canola diseases in Canada. This disease, caused by the fungus Sclerotinia sclerotiorum, is heavily influenced by environmental conditions leading up to and during the flowering period of canola, which can make predicting outbreaks difficult. Control of this disease can be achieved with risk assessment tools, fungicides, and partial resistance available in some canola cultivars.
Apothecium
Sclerotia overwinter in soil
The stem rot fungus overwinters
as sclerotia in the soil or in stubble
at the soil surface.
Ascospores
Apothecium
Formation of apothecia
Apothecia germinate from sclerotia under moist plant canopy and release ascospores.
Distribution of infection
Ascospores germinate, infect the petal and spread to adjacent tissues of healthy leaves and stems by direct contact.
Distribution of fungal lesion
The lesions progress up and down the stem. At this stage, wilted leaves can be visible.
Formation of new sclerotia
The infected stem–bleached and brittle–forms new sclerotia, which return to the soil at harvest and the cycle repeats.
MURAT YÜKSELIR / THE GLOBE AND MAIL,
SOURCE: CANOLACOUNCIL.ORG
Sclerotinia stem rot is one of the most economically significant canola diseases in Canada. This disease, caused by the fungus Sclerotinia sclerotiorum, is heavily influenced by environmental conditions leading up to and during the flowering period of canola, which can make predicting outbreaks difficult. Control of this disease can be achieved with risk assessment tools, fungicides, and partial resistance available in some canola cultivars.
Apothecium
Sclerotia overwinter in soil
The stem rot fungus overwinters
as sclerotia in the soil or in stubble
at the soil surface.
Ascospores
Apothecium
Formation of apothecia
Apothecia germinate from sclerotia under moist plant canopy and release ascospores.
Distribution of infection
Ascospores germinate, infect the petal and spread to adjacent tissues of healthy leaves and stems by direct contact.
Distribution of fungal lesion
The lesions progress up and down the stem. At this stage, wilted leaves can be visible.
Formation of new sclerotia
The infected stem–bleached and brittle–forms new sclerotia, which return to the soil at harvest and the cycle repeats.
MURAT YÜKSELIR / THE GLOBE AND MAIL,
SOURCE: CANOLACOUNCIL.ORG
Sclerotinia stem rot is one of the most economically significant canola diseases in Canada. This disease, caused by the fungus Sclerotinia sclerotiorum, is heavily influenced by environmental conditions leading up to and during the flowering period of canola, which can make predicting outbreaks difficult. Control of this disease can be achieved with risk assessment tools, fungicides, and partial resistance available in some canola cultivars.
Ascospore distributes on petals
The windborne ascospores adhere to flower petals and or other organic material.
Distribution of infection
Ascospores germinate, infect the petal and spread to adjacent tissues of healthy leaves and stems by direct contact.
Distribution of fungal lesion
The lesions progress up and down the stem. At this stage, wilted leaves can be visible.
Ascospores
Apothecium
Sclerotia
Formation of apothecia
Apothecia germinate from sclerotia under moist plant canopy and release ascospores.
Sclerotia overwinter in soil
The stem rot fungus overwinters
as sclerotia in the soil or in stubble
at the soil surface.
Formation of new sclerotia
The infected stem–bleached and brittle–forms new sclerotia, which return to the soil at harvest and the cycle repeats.
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: CANOLACOUNCIL.ORG