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What are you waiting for?
GROW.
6 12 15
CORN
Growers starting to think of what soybeans to plant for the coming season, TopCropManager has compiled a list of the latest soybean varieties available for the 2026 growing season in Eastern Canada. All information has been provided by each of the respective seed companies.
Vol. 51, No. 4
6 What’s new in corn?
Explore the latest varieties available for Eastern Canada.
FERTILITY
& NUTRIENTS
8 O ptimizing nitrogen f ixation for soybeans
Fine-tuning best practices for soybean nodulation, nitrogen uptake and yields in the Maritimes.
PESTS
& DISEASE
12 B etter solutions for BT resistant corn ro otworm and western b ean cutworm
University of Guelph researcher investigating alternative control inputs and scouting optimization.
PHOTO CONTEST
15 Taking the season sky-hig h
2025 photo contest captures another busy growing season.
CROP BREEDING
16 G rappling with a challenging fungal foe
Working towards improved white mould resistance in Ontario soybean varieties.
ON THE COVER: Photo contest winnerNorthern lights dancing behind farm silos.
Photo courtesy of Joanna Wallace.
FROM THE EDITOR
by Jillian Filmer
THAT’S A WRAP ON 2025
Here’s to finishing another year, another growing season and, hopefully by the time you get this issue, another harvest. 2025 sure has turned out to be a memorable one.
Earlier this year, U.S. President Donald Trump announced a 25 per cent tariff for imports on select Canadian goods, resulting in a cascading effect of new and retaliatory tariffs, and tension amongst trading partners all around the globe. Add in an incredibly dry and hot summer for Eastern Canada and you’ve got the perfect storm.
But with uncertainty comes new opportunity. The Canadian federal government seeks to expand upon and build new trading partnerships to protect and build resiliency within the Canadian economy. As I write this, the Minister of Agriculture and Agri-Food is in China, meeting with Chinese government officials to strengthen agricultural trade efforts between the two nations. As for weather extremes, this highlights the importance of research, the development of new innovations, and even subsidy programs, to mitigate risk.
Take the Toronto Blue Jays for example. They did not come close to securing a playoff spot last season. And, speaking as a diehard fan, I think there was a high level of uncertainty on how this season would go. But with some trades and necessary roster moves, they earned the ALCS championship title and made it to Game 7 of the World Series. Though the result wasn’t what most had hoped for, the Jays persevered amidst a shaky start to the season.
Now let’s talk about 2026. Your planning is likely underway, but this issue’s stories may spark some new ideas for the coming season. Explore the latest in corn varieties for Eastern Canada on page 6 and visit topcropmanager.com to see the latest in soybean varieties. Read about best practices for improving nitrogen fixation in soybeans (page 8), breeding research for white mould resistance in soybeans (page 16) and potential solutions to improve pest management in corn (page 12). Looking ahead, I want to know your feedback and thoughts. How can we do better, and if there is a story or an important issue you think should be featured in Top Crop Manager, email me at jfilmer@annexbusinessmedia.com. All the best for a prosperous 2026!
What’s new in corn?
Explore the latest corn varieties available for Eastern Canada.
BY JILL FILMER
If corn’s part of the rotation for next year, look no further. Top Crop Manager has compiled a list of the latest corn varieties available in Eastern Canada. All information has been provided by each of the respective seed companies.
DEKALB
DKC069-10RIB (2025 CHU) is a VT Double Pro hybrid with top end yield potential for this maturity, excellent emergence and seedling vigour, along with excellent grain quality and test weight.
DKC074-82RIB (2125 CHU) is a VT Double Pro hybrid with excellent yield potential, very good emergence and seedling vigour.
DKC081-18RIB (2450 CHU) is a VT Double Pro hybrid with strong yield potential, very good staygreen and late season intactness.
DKC082-21RIB (2475 CHU) is a Trecepta hybrid providing excellent above ground insect pest protection, very good staygreen at the end of the season and good grain quality with strong test weight.
DKC094-94RIB (2850 CHU) provides the VT4PRO trait for robust above and below ground insect protection, high yield potential with a girthy ear and very good flex, and a strong overall disease package.
DKC100-01RIB (3025 CHU) provides the VT4PRO trait for robust above and below ground insect protection, very solid yield potential, and very good seedling vigour and emergence.
DKC102-02RIB (3100 CHU) is a SmartStax PRO hybrid that brings excellent protection against corn rootworm. It provides very good yield potential and very good staygreen with excellent drydown.
DKC56-26RIB (3200 CHU) is a Trecepta hybrid with excellent yield potential, stable performance under stressed conditions and western bean cutworm control.
DKC107-84RIB (3200 CHU) is a SmartStax PRO hybrid with excellent top end yield potential, very good emergence and seedling vigour. It has excellent poten-
tial for dual purpose.
DKC110-10RIB (3300 CHU) is a StartStax hybrid with strong yield potential, test weight and agronomic package. It has excellent potential for dual purpose.
MAIZEX
MZ 1255DBR (2050 CHU) is a VT Double PRO hybrid grain corn with industry-leading yield performance. It has rapid seedling vigour to maximize potential and is a dual-purpose silage option.
MZ 1397DBR (2150 CHU) is a VT Double PRO hybrid grain corn that sets grain early for risk management and has excellent fall intactness for efficient harvest.
MZ 3006DBR (2700 CHU) is a VT Double PRO hybrid grain corn with industry-leading yield performance with strong stay-green that supports yield potential.
MZ 3717SSP (2900 CHU) is a SmartStax Pro hybrid grain corn with industry-leading corn rootworm protection and exceptional stay-green to promote full yield potential.
MZ 4799SMX (3250 CHU) is a SmartStax hybrid grain corn with market-leading DON tolerance with open husks for rapid dry down. It’s also a dual-purpose silage option.
ABOVE Corn trial in Ridgetown, Ont.
Photo courtesy of Jill Filmer.
PIONEER
P71231PCE (2000 CHU) is a PowerCore Enlist hybrid with excellent yield potential for the maturity. It features a strong disease package with very good resistance to Northern corn leaf blight.
P75303PCE (2150 CHU) is a PowerCore Enlist hybrid with excellent yield potential for maturity with early flower, good test weight and good stalk strength.
P78150PCE (2250 CHU) is a PowerCore Enlist hybrid with excellent yield potential for maturity with good stalk and root strength. It provides good resistance to Northern corn leaf blight.
P85199PCE (2500 CHU) is a PowerCore Enlist hybrid with very good drought tolerance and above average resistance to Northern corn leaf blight at 85CRM.
P91719AM (2750 CHU) is a high yield potential hybrid that provides a good disease package with very good resistance to Northern corn leaf blight and tar spot, along with very good root strength.
P98125PCE (2925 CHU) is a top end performer with AquaMax drought tolerance and the PowerCore Enlist trait, providing strong roots, stalks and good stress emergence.
P98125V (2925 CHU) is a top end performer with AquaMax drought tolerance and the Vorceed Enlist trait, providing strong roots, stalks and good stress emergence.
P9955V (2950 CHU) provides top end yield performance and strong
agronomics in the Vorceed Enlist trait, including solid root and stalk strength with a moderate plant stature.
P01851PCE and P01851V (3000 CHU) provide high yield potential with good root strength and very good resistance to Northern corn leaf blight. Available both in the Power Core Enlist and Vorceed Enlist trait options.
P03115V (3100 CHU) is a Vorceed Enlist corn hybrid offering stable performance under stress and strong top-yield in more favorable conditions. It brings a good disease package.
P07147PCE (3250 CHU) is a PowerCore Enlist full season hybrid with good stress emergence and balanced agronomics.
P10300PCE (3350 CHU) is a full maturity hybrid with top end yield potential, above average drought tolerance available with the PowerCore Enlist technology, and a solid disease package.
P10796PCE (3350 CHU) is an early silking 110 CRM product that offers consistent performance with very good drought tolerance and very good resistance to Northern corn leaf blight.
PROUD TO BE PART OF YOUR STORY
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Optimizing nitrogen fixation for soybeans
Fine-tuning best practices for soybean nodulation, nitrogen uptake and yields in the Maritimes.
BY CAROLYN KING
Rhizobia bacteria can be a valuable partner in soybean production by supplying nitrogen to their host plant over the growing season.
Bradyrhizobium japonicum, the rhizobia species used in soybean inoculants, forms nodules on the plant’s roots. In those nodules, the rhizobia convert nitrogen from the atmosphere into nitrogen compounds that the plant can use. But various factors can influence the nitrogen benefits to the plant. Now a project is looking into how to make the most of this partnership for soybeans grown under Maritime soil conditions.
“The steps to establish the relationship between the plant and the rhizobia bacteria to form these nodules are actually quite complex,” explains Tandra Fraser, an Agriculture and Agri-Food Canada (AAFC) soil microbiologist in Charlottetown who is leading this project.
“Soybeans regulate this signalling and nodulation early in the growing season. … Previous research has shown that certain conditions – including high available nitrogen in the soil and lower soil pH – can disrupt the signalling and reduce nitrogen fixation and supply to the plant later in the growing season.”
In terms of soil pH, she notes that most soils in the Maritimes tend to be acidic, and most producers apply lime to raise the soil pH level and improve nutrient availability. For soybeans, a soil pH around 6.5 is considered opti-
mal.
On the other hand, some potato producers keep their soil pH at a slightly lower level because the acidity can help control potato scab in the field. So, if they have soybeans in their potato rotations, these growers might prefer to apply less lime for the soybean year of the rotation.
“At present, the majority of Soybean Variety Trials in the region focus on maximizing yields under optimal soil pH conditions and with a small amount of nitrogen fertilizer at planting,” Fraser says.
This approach makes sense, but it leaves an information gap for producers who are interested in how different soybean varieties would perform when the soil is slightly more acidic or when no N fertilizer is applied.
“This project aims to provide some additional information on nodulation potential and biological nitrogen supply for soybean varieties that are already being tested for yield, oil and protein content under the Maritime Soybean Variety Trials.”
PROGRESS SO FAR
The project, which runs from 2024 to 2028, includes field trials and also commercial soybean fields in the Soybean Yield Enhancement Network (YEN) in P.E.I.
The project’s small-plot, replicated field trials are taking place at AAFC’s Harrington Research Farm in
LEFT A drone image of Fraser’s soybean trial on June 26, 2025, shortly after emergence.
P.E.I. These trials involve four conventional soybean varieties (Acuna, Koa, Jago, Prostar) and four Roundup Ready varieties (DKB007-91XF, B0073EE, P007A68E, Elmo E3). These eight varieties are grown in a field with a soil pH of 5.5 (slightly acidic), under two N fertilizer rates: 20 kilograms of N per hectare (kg/ha) applied as a starter; and 0 kg/ha.
Fraser and her research group are determining nodule number and weight, plant-available N in the soil, N uptake by the plant, and soybean yield and protein, for the plots in the 5.5 pH field.
For comparison, they are also collecting samples and analyzing the same factors for the same eight varieties growing in the P.E.I. Soybean Variety Trials at Harrington. In these variety trials, the soybeans are grown in an optimal soil pH of 6.5 and with 20 kg/ha of N fertilizer. Fraser’s field trials and the Soybean Variety Trials both apply a rhizobial inoculant to the soybean seed.
As of September 2025, Fraser and her group have analyzed the 2024 field data from these trials, and the project’s 2025 field season is nearing completion.
For the project’s Soybean YEN component, Fraser’s group is analyzing soil and plant samples from commercial fields across P.E.I., determining soil pH and
available N, and counting and weighing the nodules. They obtain soybean yield and protein data from YEN. In 2024, they analyzed samples from 12 YEN fields. They are continuing this work in 2025.
Fraser’s research group also recently conducted a small growth chamber experiment looking at soil pH and nodulation. They collected soils from 30 sites across the Island with a range of soil pH levels, and then grew soybeans in those soils.
They are currently counting and weighing the nodules from this growth chamber experiment. The resulting data will give Fraser and her group a better idea of the relationship between soil pH and soybean nodulation for P.E.I. conditions.
A LOOK AT SOME INITIAL RESULTS
“For the treatments at a pH of 5.5, in the first year [of the trial at Harrington], we didn’t see any differences between the varieties that we tested in terms of nodule number or weight. But we did see a reduction in the nodules in the fertilized plots versus the plots with 0 nitrogen fertilizer,” Fraser notes about preliminary results from the project’s first year.
“Looking at the differences from soil pH, the yields
were higher in the soybeans grown at pH 6.5 as compared to 5.5. However, there were also some differences in weed control between those plots, which I think likely contributed to the yield differences between the two pH levels.”
Unexpectedly, the nodule numbers and weights were actually higher in the 5.5 pH field. However, it turned out that the 6.5 pH field had more available N than the 5.5 pH field due to previous crop management. The data showed the nodule counts and weights went down as the available N went up, suggesting that the increased nodulation in the 5.5 pH field was due to its lower available N rather than to its lower pH in this case.
In the YEN fields for 2024, the number of nodules per plant ranged from 23 to 99, and available N ranged from 1.1 to 4.8 milligrams per kilogram of soil. As expected, the nodule numbers tended to decrease as the available N in the soil increased. (They have not yet completed the analysis of the data related to the effect of soil pH on nodulation.)
COMING UP NEXT
Fraser and her research group will continue the field trials in 2026 and 2027. She says, “By running the multi-year trials, we can get a better idea of the effects under different weather situations.”
They will also continue to collect data from new YEN sites on the Island in each year of the project.
By the end of the project, Fraser hopes to have a substantial dataset that will allow her group to tease out a clearer picture of the effects of soybean variety, available N, soil pH and weather conditions on soybean nodulation, N fixation, N uptake, yield and protein.
Fraser is also hoping to do some DNA analysis to get a better understanding of soybean rhizobia performance under Maritime growing conditions.
“Bradyrhizobium japonicum bacteria are not naturally occurring in our soils, so they need to be applied as an inoculant. This is especially true if soybeans have never been grown in a field,” she explains.
“However, over time, if soybean has been planted in a particular field many times, it is possible that the rhizobia population could build up in the soil and could form nodules on soybean roots even if the grower does not apply an inoculant every year. But if you apply an inoculant, you can be confident that the rhizobia are there and it is usually going to be more effective.”
The length of time that rhizobia from inoculants will persist in the soil after an inoculated crop has been harvested depends on several factors such as weather conditions, soil conditions, and the number of years since soybeans were last grown in the field. Another consideration related to these residual rhizobia populations is that some of these rhizobia might gradually adapt to the local growing conditions so they might differ from the original inoculant strain in terms of their ability to compete for places on the plant’s roots and/or their effectiveness in providing N to the plant.
Fraser says, “For the YEN fields, we could potentially look at the rhizobial strains by extracting the DNA [from the nodules] and then sequencing it to see if there is any difference between commercial fields in what is being nodulated on the plant, whether it is the commercial inoculant or if there are some changes in the strains over time.”
LOOKING AHEAD
The information resulting from this project could help Maritime soybean growers in making decisions on variety selection related to N fixation and
performance under lower soil pH conditions, as well as information to help in decisions around N fertilizer applications and liming.
“The aim of this project is [to] provide producers with locally relevant data on the best management practices for soybean production in Prince Edward Island and to improve the understanding of the relationship between the soil conditions and nodule development and then yield,” concludes Fraser.
“That way growers will know when inoculation or nitrogen fertilizer is most critical or when they could potentially reduce their input costs. … And for potato farmers who have soybeans in their potato rotations, we’re hoping to provide information on which soybean varieties produce better yields in a lower soil pH.”
Fraser’s project is funded by the Atlantic Grains Council (AGC) and AAFC. Collaborators on this project include: Dan MacEachern, a biologist at AAFC Charlottetown who is managing the agronomy aspects of the field trials; Aaron Mills, an agronomist at AAFC Charlottetown, and Steve Howatt, AGC’s YEN coordinator, who are collecting the soil and plant samples from the YEN fields.
ABOVE One of the soybean plants grown at the optimal soil pH of 6.5 in the trials at Harrington.
PRIDE SEEDS
A4226G2 (2125 CHU) is a VT Double PRO hybrid grain corn that delivers strong standability, excellent spring emergence, early flowering and very good early-season vigour.
A5175G2 RIB (2475 CHU) is a VT Double PRO hybrid grain corn with excellent emergence, early vigour, and demonstrates strong late season health and harvestability.
A5580G4 RIB (2650 CHU) is a Trecepta hybrid grain corn with strong seedling vigour and protection against western bean cutworm.
A5775G2 RIB (2650 CHU) is a VT Double PRO hybrid grain corn with excellent yield performance under stress. It provides a medium plant stature with excellent feed value as a silage hybrid.
A6226G2 RIB (2800 CHU) is a hybrid grain corn that delivers outstanding yield for its maturity with good drought tolerance. It’s supported by strong stalks and roots and a solid response to fungicide.
A6846G6 RIB (2950 CHU) is a SmartStax hybrid grain corn that offers trait protection against western bean cutworm and corn rootworm. Consider it as a reliable dual-purpose option.
A6975G2 RIB (2975 CHU) is a VT Double PRO hybrid featuring above ground pest protection. It demonstrates good emergence across spring soil conditions, and strong stalks and roots.
A7275G2 RIB (3150 CHU) is a VT Double PRO hybrid with excellent yield potential for maturity with good dry down, and ability to flex in
kernel depth late in season.
A7599G9 RIB (3225 CHU) is a SmartStax PRO hybrid grain corn with excellent disease tolerance. It has an early flowering for maturity rating for a longer grain fill period.
AS1058G2 EDF RUB (2350-2525 CHU) is a VT Double PRO hybrid for silage feed. It features integrated above ground pest protection and balance feed value with low to medium plant populations.
A7275G2 RIB (3075 CHU) is a VT Double PRO hybrid for silage feed that provides excellent yield potential for maturity with good dry down, and the ability to flex in kernel depth late in season.
WINFIELD UNITED
CP2925TRE (2700 CHU) is a Trecepta hybrid with new high yield potential in the 89-day growing regions. It’s a versatile hybrid that is flexible on soil types and has above average staygreen.
CP3540VT4P (2850 CHU) is a VT4PRO hybrid that fits Ontario/Quebec well. It shows high yield potential coupled with drought tolerance and fast dry down for timely harvest.
Better solutions for Bt resistant corn rootworm and western bean cutworm
University of Guelph researcher investigating alternative control inputs and scouting optimization.
BY MATT MCINTOSH
Corn rootworm and western bean cutworm pose serious risks to Canadian corn growers, particularly as resistance to go-to controls continue to proliferate, and when environmental conditions impede optimal insecticide application timing.
University of Guelph researcher Jocelyn Smith, assistant professor of field crop entomology, is evaluating how growers can get a leg-up on corn rootworm and western bean cutworm through alternative control methods. However, as resistance to go-to controls continue to proliferate, the fundamentals of regular crop rotation and scouting remain critical.
CURRENT ROOTWORM CONTROLS
Ontario is home to western corn rootworm and northern corn rootworm. Adults of the former are yellow with three wavy black stripes on their wings, while the latter are green. Adults emerge from the soil in mid-summer to feed on pollen, silk and leaves.
The larvae of both rootworm species inhibit nutrient and water uptake by eating the roots of corn plants, resulting in poor growth. Significant yield losses – 15 to 18 per cent for every damaged node of roots – are often incurred before any symptoms of root damage are visible. Harvest losses from subsequent lodging are also possible.
“Our primary tried-and-true way to manage rootworm is crop rotation. There is no rotation-resistant rootworm in Ontario as of yet. Rotation to any crop other than corn causes high larvae mortality,” says Smith. “For growers that don’t have rotation as an option, they have primarily Bt corn hybrids. But anywhere there’s concentrated areas of livestock producers, where there’s a lot of continuous corn for livestock feed, we’re getting a lot of resistance developing to current Bt toxins.”
New RNAi traits effective at controlling corn
rootworm are now available, providing growers with additional options for repeated corn crops. Smith cautions against relying too heavily on new control traits, however.
“We’re worried there won’t be a long lifespan for these traits if growers continue growing corn after corn. We really encourage rotation. Do not go more than three years with any of the RNAi traits,” she says.
“Rootworm resistance levels in Ontario are increasing. The same thing is happening in Quebec. The Maritimes less so, but rootworm populations are
ABOVE Western bean cutworm feeding on ear of corn.
All photos courtesy of Jocelyn Smith.
starting to increase there. We all need to be thinking long-term rootworm management. We cannot rely just on the Bt traits because rootworms are notorious for developing resistance to everything.”
NEW ROOTWORM TOOLS
One alternative rootworm option is a granular pyrethroid insecticide, applied at planting. Smith’s research shows this is effective at eliminating rootworm larvae, but it requires the use of insecticide boxes on planters – something most growers eschewed long ago, but which some are now bringing back. Applying granular pyrethroids at planting should not be used in conjunction with Bt corn either, as doing so further compounds selection pressure for Bt resistance.
New liquid formulation insecticides are also being evaluated, as is the application of entomopathogenic nematodes – soil organisms that infect larvae – as a biological control.
“The nematodes are already native in the soil, but we’re supplementing it with reared doses of nematodes. There’s research from the United States showing this helps lower resistance issues when used with Bt
A DIFFERENCE YOU CAN SEE
traits,” says Smith, adding further data is needed before full conclusions can be made about their efficacy.
“2025 has been a very big rootworm year. The environmental conditions for their overwintering and the hatching in spring were ideal...We were having a lot of calls for high populations, lodged corn, and we collected many samples of beetle in Bt corn fields with a lot of rootworm injury…Some years are just worse than others. Often times we maybe get away with less than best management practices because the weather helps us out. But when weather aligns well, we can see how bad the problem actually is.”
LEFT Below the surface damage caused by corn rootworm.
IMPACT OF WESTERN BEAN CUTWORM
Western bean cutworm was first detected in Ontario in 2008. Cutworm larvae feeding occurs on pollen, silks, ear tip kernels, as well as further down the ear both within and outside the husk. Western bean cutworm larvae are also very mobile, capable of dispersing to multiple plants. Yield losses from the pest are estimated to
reach 15 bushels per acre.
Smith says western bean cutworm pressure in 2025 has proven to be lower than anticipated in Ontario and Quebec. The Maritimes, conversely, have experienced higher pressure. Only one effective Bt toxin currently exists for the pest, and relatively few hybrids with the trait are available.
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“Growers really need to scout to see if they need to apply insecticide,” she says, referring to in-season applications. The trouble is, finding western bean cutworm egg masses is difficult because they are small, on the underside of leaves, and thus hard to see.
Part of Smith’s current research involves the identification of characteristics that make fields more or less attractive for western bean cutworm to lay eggs. Distance from tree lines, soil texture, topographical characteristics, plant stage or height, and nutrient levels are examples of the ten to twelve different characteristics currently being considered. Data is being gathered via drone equipment with NDVI imagery capability. The hope is to inform prioritized scouting by determining which locations western bean cutworm are most likely to be found.
“We didn’t have a lot of data because of the low pressure from western bean cutworm this year, so at this point, scouting has to be done the old-fashioned way,” says Smith, adding they may increase the number of field characteristics in their analysis as more information is gathered.
“We’ve also been hearing from some growers that optimal insecticide timing is challenging, so we want to optimize spray timing recommendations as well. Scouting is difficult and the timing is so tricky. Growers that do scout might not just hit that timing correctly.”
ABOVE In-field damage caused by corn rootworm.
Taking the season sky-high
2025 photo contest captures another busy growing season.
BY JILL FILMER
Harvest’, amongst breathtaking skies and views, seemed to be the trending theme featured in the entries from Top Crop Manager’s 2025 photo contest. The winning photo gracing this issue’s cover displays silos against a sky of Northern Lights – taken by Joanna Wallace of Seaforth, Ont. Here are a few honourable mentions.
TOP/MAIN Soybean harvest at sunset.
MIDDLE A storm rolling in.
BOTTOM ROW The final stage of wheat before harvest time; Finishing up corn planting; Harvesting wheat.
Grappling with a challenging fungal foe
Working towards improved white mould resistance in Ontario soybean varieties.
BY CAROLYN KING
When it comes to developing soybean varieties with resistance to white mould, “the work is cut out for the breeders. But it is possible, and we are making progress. It is just a little more challenging than some other diseases in soybean,” says Istvan Rajcan.
Rajcan is speaking from a wealth of experience in soybean breeding and genetics, including leading a soybean breeding program at the University of Guelph for more than 27 years. His program, which has developed more than 87 soybean varieties, focuses on high yielding, high quality, disease-resistant varieties suited to Ontario growing conditions.
White mould, a very damaging disease that reduces soybean yield and quality, is one of his program’s disease resistance priorities. Rajcan and his research group are using molecular tools and other advanced approaches to develop soybean varieties that are better able to withstand the disease.
Also known as sclerotinia stem rot, white mould is caused by the fungal pathogen Sclerotinia sclerotiorum. Disease symptoms in soybean can include lesions on the stems, pods and leaves, white mouldy areas, wilted and dying leaves, and in the late stages of disease development, the formation of black resting bodies called sclerotia, which can drop in the field to cause infection in future years.
Although crop varieties with genetic resistance to any given disease offer an easy, environmentally friendly way to manage that disease, Rajcan explains that resistance to white mould is especially helpful for a couple of reasons.
“White mould can be controlled in soybean crops with a fungicide, but these fungicides have to be applied in a
timely manner. Sometimes that is difficult if scouting misses the disease symptoms early; the disease could develop fast and then the fungicide application might be too late, and the cost of application becomes a factor as well,” he says.
“Secondly, white mould is a sporadic and unpredictable disease. Even when we think we know what environmental conditions promote this disease – in most cases it is cooler weather and moist conditions – there have been some years when we had exactly those conditions and no disease, and other years when it was the opposite.”
However, when a variety has white mould resistance, the plants are ready to fight back if the fungus does show up.
TACKLING SOME BREEDING CHALLENGES
A key challenge in breeding for white mould resistance is that white mould resistance involves many genes on many different chromosomes, with each gene having a small effect.
Due to this complexity, no soybean varieties are completely resistant to white mould, and breeding for partial resistance, while difficult, is the best approach currently.
“Trying to build all those genes into a new variety, combining their effects to have a variety that is partially resistant to white mould, requires a significant effort,” Rajcan notes. “And in some contexts, a certain gene may work in one genetic background but may not work in another.”
Another challenge is that field screening of breeding materials for white
ABOVE To assess white mould resistance in the 193 lines, each line was inoculated with the pathogen; this plant shows symptoms of white mould after inoculation.
mould resistance can be difficult because of the disease’s unpredictability. Even in white mould disease nurseries, breeders can’t always be sure of getting the strong disease pressure needed to accurately distinguish partially resistant lines from susceptible ones.
That’s why Rajcan’s group uses indoor screening methods where the plants are inoculated with the fungus under controlled conditions. “Those results from indoor studies tend to be consistent and transferable from one lab to another,” he explains. There is a small possibility that the indoor results might not always correlate to natural outdoor infection conditions, but he says, “We think if we inundate the plant with inoculum of the fungus in the indoor screening and it still responds well, then the chances of that plant behaving as a susceptible plant in the field are much lower.”
As well, his group uses DNA markers to screen for white mould resistance without having to expose the plants to the disease. Rajcan says, “If we have a DNA marker that is associated with partial resistance to white mould, we can do an assay to determine whether the DNA in the plant carries the susceptible ‘allele’, or version of the gene, or the resistant allele, and then select those plants that have the resistance and discard the susceptible ones.”
Markers are particularly helpful when breeders are aiming to stack several different white mould resistance genes in a variety. To do that, they need to know which particular resistance genes are present in the progeny, and they can’t tell that from the plants’ resistance responses in a field or lab trial.
Along with markers, Rajcan’s program uses other molecular genetics tools, such as genome-wide association studies (GWAS) and gene expression studies, in developing varieties with resistance to white mould and other key diseases.
DISCOVERING NOVEL RESISTANCE
A great example of the use of these types of molecular tools for investigating white mould resistance is the research by one of Rajcan’s previous PhD students, Deus Mugabe. Now a scientist with Bayer Crop Science Canada, Mugabe’s PhD work resulted in the discovery of new white mould resistance in Canadian soybeans.
This research involved a panel of 193 soybean lines that are representative of the genetic diversity in Canadian soybean varieties, with a focus on maturity groups 000 to I. The lines in this panel were also chosen to encompass a diversity of responses to white mould, ranging from partially resistant to highly susceptible. Each line was genotyped by sequencing its DNA.
In controlled environment conditions, Mugabe inoculated each of the lines with the white mould pathogen. Then he rated each line’s resistance or susceptibility to the disease by measuring the length of stem lesions.
A DEKALB roundtable discussion with Eastern Canadian Agronomists on Harvest Insights
Sponsored by
Presented by
Bob Thirlwall Phil Nadalin Katie Macfarlane Gabrielle Croft
RIGHT Each line’s resistance or susceptibility to the disease was assessed by measuring the length of stem lesions.
Next, Mugabe brought together this white mould response data and the genotype data in a GWAS analysis. GWAS is a way to find which alleles are associated with a specific trait of interest, in this case white mould resistance. For instance, if a certain allele is present in all the soybean lines with partial resistance and absent in the susceptible lines, then that helps researchers to draw the conclusion that the allele may be conferring some white mould resistance.
Through the GWAS analysis, Mugabe identified two genetic loci (specific locations in the plant’s DNA) on chromosomes 2 and 9 that are associated with white mould resistance. These two resistance loci have never been reported before.
Then he conducted several studies to look at the genes in the vicinity of those two loci to try to determine which particular genes are conferring the resistance. He identified several possible candidate genes based on known roles of these genes in a soybean plant’s defences against disease. He also carried out gene expression studies to see how these candidate genes responded after the plants were inoculated with the white mould pathogen.
Now Rajcan’s research group is conducting further studies to confirm which candidate genes are conferring the resistance. And, using DNA markers resulting from Mugabe’s work, they will be making crosses to incorporate these novel white mould resistance genes into new soybean varieties.
IMPROVING BREEDING EFFICIENCIES
In a recently completed project, Rajcan’s group used marker-assisted breeding for resistance to white mould and soybean cyst nematode.
Until this project, his group had been using the previously identified disease resistance markers at the F 5 stage, the fifth generation of offspring from a cross. But in this project, they used the markers at F4. This allowed them to discard all plants without the resistance alleles earlier in the process, saving time and resources by focusing on the materials with the most promise for developing disease-resistant varieties.
The white mould portion of the project involved crosses made between high yielding, high quality, food grade parents and parents with partial resistance to white mould. Rajcan’s group used a marker developed by a colleague to select for the white mould resistance gene that was in an old Agriculture and Agri-Food Canada variety named Maple Donovan.
With that marker, they identified some materials with the resistance gene, and then they tested those materials to confirm the partial white mould resistance.
Since then, Rajcan and his group have been evaluating those partially resistant lines for yield, quality and all the other traits needed in Ontario soybean varieties, keeping the best lines and culling the rest. They are nearing the final stages towards developing commercial varieties and they have some advanced breeding lines with partial white mould resistance that look pretty good.
TAPPING INTO CHINESE GENETICS
White mould resistance is also going to be part of Rajcan’s current ‘allele mining’ project, which runs from 2023 to 2029. This project is tapping into
Chinese soybean genetics for novel genes and alleles related to yield, protein content, oil content, drought tolerance and disease resistance.
“When soybeans were brought to Canada more than 100 years ago, what was brought was only a subsample of what is found in China. There is a much greater diversity of genetics in China that we haven’t tapped into,” explains Rajcan.
This research had its beginnings with a gift of soybean seed to Rajcan from his Chinese colleagues in northeast China. Those Chinese varieties became part of a Canadian-Chinese genetic diversity panel assembled by Rajcan’s group. This panel consists of about 200 different soybean lines, including elite Chinese varieties, elite Canadian varieties, and the progeny of crosses between the Canadian and Chinese varieties.
The project’s disease resistance component includes the pathogens causing soybean cyst nematode (study completed) and Phytophthora root rot (study underway); the white mould study using this panel will be done in the coming years. These studies involve GWAS analysis to find genes and alleles associated with the disease resistance.
Overall, Rajcan and his group are making significant advances in developing soybean varieties with improved white mould resistance – along with all the other traits that growers, processors and consumers are looking for.
The funding agencies making Rajcan’s white mould research possible include: Grain Farmers of Ontario, SeCan, Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Agricultural Partnership program and the Ontario Agri-Food Innovation Alliance program. He also thanks his graduate students, summer students, technicians and research associates, both current and former, for their work contributing to development of soybean varieties with white mould resistance.
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