In pursuit of hirsute canola
An update on the development of hairy canola for fighting flea beetles and other pests.
December 4, 2020 By Carolyn King
Hairy canola, a tool for managing one of the worst insect pests of canola, could finally be coming into its own. After many years and numerous challenges, the latest hairy canola lines being developed by Agriculture and Agri-Food Canada (AAFC) have characteristics that could spark the interest of canola breeding companies.
AAFC’s research shows these non-genetically modified (non-GM) lines deter flea beetle feeding and might also help manage other tough-to-control canola pests. So, hairy canola could become a valuable addition to pest management toolboxes, especially if insecticide options become more limited due to regulatory changes or to development of insecticide-resistant canola pests.
Advances and hurdles
“This research actually began decades ago with the work of two AAFC scientists, Bob Bodnaryk and Bob Lamb, in Winnipeg. They were looking at wild Brassicas, the wild relatives of canola, to find plants that were resistant or less susceptible to flea beetles. They found a fair number of Brassicas that had noxious chemicals that discourage insect feeding, such as the glucosinolates that we have bred out of canola. But they also found some Brassicas with hairs – the scientific term is trichomes – that seemed to deter flea beetles,” explains Dwayne Hegedus, the AAFC research scientist who is currently leading the hairy canola breeding work.
“Julie Soroka, who had been working with these two scientists, decided to further pursue this research when she transferred to AAFC’s Saskatoon centre in the 1990s. In some really interesting studies, she determined that for a flea beetle to begin feeding on a plant, it has to go through a series of steps involving landing, then tapping on the plant with its appendages, and then various types of probing and tasting. But if you disrupt a flea beetle at any stage in this ingrained process, it has to go back to step one. Hairs on a plant prevent the beetle from engaging in this process. So, rather than starve, the beetle eventually leaves the hairy plant.”
Margaret Gruber, a plant molecular biologist at AAFC-Saskatoon, began working with Soroka to see which genes were missing in canola that prevented it from forming trichomes. “Margie forged a collaboration with a scientist at Texas A&M University who had discovered a gene called GL3 that is responsible for hair production in Arabidopsis thaliana, a European Brassica weed,” Hegedus notes. “Margie put GL3 into canola, and the resulting genetically modified lines had lots of hair [all over the plants]. However, these lines were also very small and had poor growth habits.”
To overcome that problem, Gruber made another genetic modification. “She changed the expression of a gene called TTG1 so that the ratio of GL3 to TTG1 was closer to natural.”
The combination of these two modifications resulted in a hairy canola line that performed as well as Westar, the check canola variety, in terms of agronomics and oil quality. Plus, these hairy canola plants withstood flea beetles as effectively as Westar plants that had received an insecticide seed treatment.
“Margie then engaged in a very long exercise to try to get different breeding companies interested in this. And over the years it has been asked many times: why is hairy canola not yet in farmers’ fields?” Hegedus says.
He outlines some key factors: “First of all, the hairy canola that Margie and Julie developed requires not one but two different transgenic events, which is quite complicated from a regulatory perspective. As well, if the ratio of GL3 and TTG1 is off a bit you can have problems with plant development, and at times this ratio is not very stable. That is not what breeders want in their breeding programs.
“Another factor is there is a patent on GL3 at Texas A&M, so breeding companies would have to deal with that. Also, there is the issue of the registration/regulatory costs for GMOs. In addition, most of our major breeding companies are also chemical companies. If they had invested in this way of naturally reducing the impact of flea beetles, that would have been in conflict with their chemical business unit.”
However, Hegedus points out that thinking on this last issue is changing, especially since neonicotinoids – the main chemical control option for flea beetles – have come under environmental review in several jurisdictions. In Canada, some bans or restrictions on neonicotinoid use are already in place, and Health Canada’s Pest Management Regulatory Agency (PMRA) is currently reviewing neonicotinoid uses.
Towards non-GM hairy canola
Given the GM-related hurdles, Gruber and Soroka decided to see if they could develop non-GM hairy canola lines. They embarked on a very ambitious program to screen more than 1,000 Brassica lines from Plant Gene Resources of Canada to look for naturally hairy plants. According to Hegedus, the researchers found a handful of hairy lines in three species: Brassica napus (canola is a type of Brassica napus that has been bred for certain crucial quality characteristics); Brassica rapa (Polish canola was developed from this species); and Brassica villosa (a wild Brassica).
He notes, “Brassica villosa is closely related to Brassica oleracea, which is the species of most cruciferous vegetables, like cauliflower, broccoli, cabbage, kale and so on. But Brassica oleracea is also very closely related to canola. In fact, if you cross Brassica oleracea with Brassica rapa, you generate Brassica napus. So they are all part of a triangle of very closely related species, and the traits in one can be transferred to another.”
Over the next few years, Gruber and Soroka conducted various studies towards developing non-GM hairy canola lines. Hegedus, who came to AAFC-Saskatoon in 1997, worked with them on these studies. Gruber and Soroka have since retired, and Hegedus has taken up the reins of this research.
His current hairy canola project runs from 2018 to 2023 and is funded by AAFC and the Canola Council of Canada under the Canola Cluster research program. In this project, the researchers are continuing to develop non-GM hairy canola lines through work with the naturally hairy Brassica napus, Brassica rapa and Brassica villosa lines. Hegedus says these lines have some differences in their hair characteristics. Brassica villosa has abundant hairs that blanket all of the plant’s surfaces in a soft, velvety covering. The hairs on the B. rapa and B. napus lines are prickly, erect, less abundant, and occur only on the leaves.
Hegedus and his project team are identifying the genes that control hairiness in these different lines, and they are mapping and moving those genes into a Brassica napus background that commercial breeders could use for crossbreeding to move the trait into their elite canola lines. The team is also developing genetic markers to make it easier to track the presence of these genes in the progeny of different crosses and backcrosses.
The project also includes greenhouse and field trials to see how effectively the lines from the different crosses repel flea beetles.
“Chrystel Olivier, who is providing entomology expertise on this project, has discovered some of our early lines from some of our crosses show fairly significant deterrence to flea beetles,” Hegedus notes. “But in the lines where only the leaves have hairs, the beetles just go to the stems and begin feeding there. So we now know that we need trichomes over the entire surface of Brassica napus, like Brassica villosa has.”
As a result, the team is mapping the genes that govern trichome formation as well as the genes that regulate trichome abundance and distribution, with the goal of combining both characteristics in a single background.
Interest from breeders
“We’re in a position now where I think we could begin providing some of our very early material to breeders. We have had some discussions with private sector breeders about this. They have told me that they would actually prefer the early material because then they can begin doing their own crosses,” Hegedus explains. “Even if they want to develop the markers themselves so they can do things on proprietary basis, our work on the initial crosses is very useful to them. It helps establish just how complicated hairiness might be; for instance, if it is one gene or two genes or three genes.”
By early 2020, Hegedus and his project team were feeling very enthusiastic about their progress on hairy canola. Then COVID-19 restrictions halted their work, resulting in the loss of a field season. Hegedus is hopeful to be in the greenhouse during the winter. “We were able to collect seed from some of our plants and populations, but all that has to be restarted.”
Deterrence for more than flea beetle?
In a related project, Olivier and her research group are conducting lab and field experiments with hairy Brassica napus and Brassica villosa to assess feeding and egg-laying behaviour of striped flea beetles, diamondback moths and aster leafhoppers.
“These three insects are major canola pests, and all three of them are difficult to control,” Olivier says. “At present, there are no canola varieties that are resistant to any of these three insects. So far, no models have been developed for any of them that can predict their populations from one year to the next. With grasshoppers, you can look at the number of eggs and predict how large the population will be in the following year, but we can’t do that for these three insects.”
Plus, each of these pests has its own particular control challenges.For flea beetles, a neonicotinoid seed treatment is used to help manage the pest during the seedling stage when the plants are most vulnerable. “This seed treatment provided better results when crucifer flea beetles were the main species of concern, but we have had a shift toward striped flea beetles in many regions of the Prairies,” she notes. “Striped beetles emerge earlier and are less susceptible to the neonics. Especially where this species shift has occurred, a seed treatment may not be sufficient to control the pest and you may need to also spray the crop.” As well, the findings from the current Canadian review of neonicotinoids might impact the use of neonicotinoid seed treatments in Prairie canola crops.
“For the diamondback moth, a lot of its populations are starting to be resistant to insecticide products. Also, these insects have several generations per year, which means you need to monitor and spray your crop to control the population,” Olivier says.
“Aster leafhoppers spread the aster yellows disease. Some of the bioassays that we conducted a few years ago showed that this insect can transmit the disease to a plant in less than 10 hours. So the window to spray is extremely short.”
Olivier’s project is funded by the Canola Agronomic Research Program in partnership with Alberta Canola and SaskCanola. This project started in 2018 and goes to 2021. So far, she and her group have mainly been working on lab bioassays with flea beetles and diamondback moths.
“The bioassays involve using an environmentally controlled growth chamber. We put cages with the insects and the plants in the chamber, and we monitor the insects’ feeding behaviour, feeding damage, the number of eggs, how they fly, and how they move from one plant to the other,” she explains. “The bioassay can be a choice experiment or a no-choice experiment. A choice experiment is when we put, for example, a flea beetle in the cage with a hairy canola plant and a glabrous (non-hairy) canola plant. And we see what the flea beetles do – do they go on one plant or the other, do they prefer to feed on one and not the other, do they prefer to lay eggs on one and not the other, do they prefer to feed on some part of the plant and not the other, and so on. In a no-choice experiment, we use only one type of plant, and we see what the insects do.”
These experiments are also evaluating the effect of plant growth stage, temperature and soil moisture on insect behaviour.
“We started with the striped flea beetle bioassays because that species is the main concern for many growers. We found that the striped flea beetles tend to avoid the hairy part of the plant. So when we put a hairy canola and a glabrous canola in the cage, the beetles usually don’t want to stay on the hairy one, and they go on the glabrous one, which is very good,” Olivier says.
“When we put only hairy canola in the cage, the flea beetles don’t like the hairy parts. They don’t even particularly like the cotyledons, which is weird because the cotyledons do not have hairs. The beetles go from the cotyledons and hairy leaves to the glabrous stem. And they clip the stem, killing the stem, which is not good.”
These findings are why Hegedus’s team is now working to develop hairy canola lines that have hairs all over, not just on the leaves. Olivier notes that the Brassica villosa plants, which are hairy all over, had very little to no flea beetle feeding.
The diamondback moth bioassays are also generating valuable results. Olivier says, “We found that the female diamondback moths absolutely love laying eggs on the hairy canola; they lay a lot more eggs on the hairy canola compared to the glabrous canola. But the good news is that the larvae have a lot of trouble walking, mining and feeding on the hairy plants. In particular, the first instar larvae, the tiniest larvae which usually mine the foliage, have a lot of trouble mining.” Those little larvae tend to die before they get much bigger.
“And when we put the bigger diamondback larvae on the hairy leaves, the larvae don’t want to have anything to do with those leaves. They prefer feeding on the glabrous leaves. So that is also good news.”
COVID-19 restrictions have limited the project’s progress this year, affecting such activities as the aster leafhopper bioassays and some field experiments.
Olivier has applied for funding for a new project to do hairy/glabrous canola bioassays with both striped and crucifer flea beetles. She explains, “These two species are both found in Prairie canola. Some crops have a lot more striped and some have a lot more crucifer. I would really like to know what happens when you put both species in the same cage.”
The more tools, the better
“The more tools we have to control these pests, the better. Hairy canola might be one of the tools that the growers could use,” Olivier says.
Hegedus notes, “Almost every single acre of canola grown in Canada has its seed treated with neonicotinoid insecticides because the flea beetle pressure is so high that it is virtually impossible to grow canola unless you do something to control this pest. If farmers in Western Canada lose this very important tool for flea beetle control, it would severely impact canola acreage.”
He points out that growers could lose the use of neonicotinoids depending on the results of the current review, but they might also lose the effective use of these products due to development of neonicotinoid-resistant insect populations.
“When you apply a chemical every year to control a crop disease or insect pest, you continually select for the individuals in the population that are more resistant to that chemical. So neonicotinoids are going to have a limited life, and they will have to be replaced by something else,” Hegedus says.
“I think it is far less likely that flea beetles will develop some sort of mechanism where they could begin feeding on hairy canola. Looking at natural mechanisms like this is really something we need to be doing.”