Clubbing Clubroot: An Update On Breeding Clubroot-Resistant Canola

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While Bayer CropScience undertakes much canola breeding research, such as in the greenhouse pictured, clubroot resistance research is conducted in a highly-secure lab to prevent the spread of the pathogen. (Photo: Bayer CropScience)

On the Prairies, clubroot appeared in Alberta in 2003, in Saskatchewan in 2008 and Manitoba in 2013. As any grower can tell you, it’s a nasty canola disease that usually worsens in a field every year, partly because the spores are very easy to spread and so hardy they can survive for up to two decades in the soil. Combine this fact with the strong prices that canola fetches these days – widely encouraging back-to-back or two-year rotations – and you have a big problem.

Companies are certainly moving as quickly as possible to produce seed with effective resistance to clubroot, but breeding to defend against this particular pathogen involves navigating a wide range of complex challenges.

“Clubroot has a very short lifecycle resulting in several generations per season,” explains Dr. Marcus Weidler, vice president of seed operationsat Bayer CropScience, “enabling the pathogen to react to changes in its environment very quickly, including new crop resistance genes.”

Dr. Jed Christianson,pathology lead at Monsanto Canada, explains that clubroot’s large and quickly-adapting population sizes means that it takes relatively long canola rotations of three or four years to see significant drops in the number of viable spores in the soil, and very long rotations of over 10 years for spores to effectively disappear.

“Each gall produced on a canola root can contain billions of spores,” he says. “So, given the numbers of spores generated, even very rare events like the emergence of individual spores that have gained the ability to infect resistant canola will happen over a fairly short number of cropping cycles. A one in a billion event doesn’t seem that unlikely to happen when you’re given 20 billion chances.”

Combine this with the fact not all clubroot pathotypes (races) have been identified, and it’s therefore difficult, explains Weidler, to develop a canola variety that is resistant to all potential pathotypes to which a plant may be exposed.

Dr. Igor Falak reminds us that it was in2013 that a new clubroot pathotype was identified, one to which all canola varieties on the market carrying resistance to the original 2003 pathotype were susceptible. Although hybrids with the initial type of resistance continue to hold their own on most infested acres, the number of fields with the new pathotype is increasing annually. Falak, senior research scientist with Corteva Agriscience, blames this situation on “years of canola-on-canola.”

In addition, he notes that although clubroot “is similar to another disease of canola (blackleg), where canola products may carry race specific resistance,” clubroot-resistant canola varieties “do not have ‘fallback’ resistance mechanisms, unlike blackleg-resistant products that also have a different type of stable resistance.”

More breeding challenges are found in the fact that because canola plants carry no clubroot resistance genes, all the major seed companies are actively testing resistance genes found in rutabaga, cabbage and turnip. However, Weidler notes that because these species are only remotely related to canola, it’s far from easy to transfer genes between them without also transferring additional unwanted genetic “baggage” that negatively impacts yield, canola quality or agronomics.

If all this wasn’t enough, clubroot is a challenging organism to deal with, having unique characteristics – described by Weidler as a form of life “somewhere between a bacterium and a fungus.”

Christianson concludes that the biggest challenge in creating clubroot-resistant canola seed is to introduce resistance “while continuing to improve hybrid performance for yield, maturity, standability, resistance to other diseases, harvestability, seed quality and all of the other attributes that are important to growers’ success.”

Breeding Steps to Develop Clubroot-Resistant Canola Seed

Christianson says the steps involved in breeding clubroot-resistant varieties are relatively simple, and that any breakthroughs relating to resistance genes “are really just the discovery and characterization of more of them through concerted screening efforts.”

The entire process is a matter of crossbreeding canola with resistant relatives through normal pollination procedures and recovering offspring that are clubroot-resistant. “Those offspring then have to be crossed with canola again and again through many generations, selecting the resistant offspring at each generation for use in the next cycle to obtain plants that maintain resistance, but have recovered the characteristics of high-performing canola,” Christianson explains.

Weidler adds that unwanted genetic material from the resistance donor that negatively impacts the agronomic performance of the offspring is removed through several crossings of the offspring with elite parent stock. “Using molecular breeding tools, we can check the progress towards the end goal,” he notes. “Ideally, only the genetic sequence conferring clubroot resistance has been transferred and no other parts of the donor genome remain in the offspring.”

Breeding Progress

DowDupontwasthe first company in Canada to market clubroot resistant hybrids in 2009 (45H29).

“Our hybrids have multi-source and multi-race resistance to clubroot, and have a high level of resistance to the most prevalent clubroot race – race 3 – along with resistance to races 2, 5, 6 and 8,” Falak notes. Pioneer has new canola hybrids that contains a new source of clubroot resistance that confers resistance to both the initial type and new pathotypes, and can be rotated with the original resistant hybrids.”

For its part, Bayer CropScience has “identified several new potential resistance sources,” says Weidler, “and we have been able to demonstrate that these are different from what is currently on the market.”

Christianson says that as Monsanto nears “actual commercial entry into the marketplace, we will have more to share about how second-generation resistance fits in with existing resistance traits to provide a sound disease management strategy.”

No matter what resistant canola varieties are marketed, no company can predict how long a new variety will last before it’s compromised. This depends on too many factors, explains Weidler, including the resistance gene, environmental conditions and management practices.

All the companies strongly agree that the existence of varieties with resistance is only part of the clubroot solution.

Weidler emphasizes the importance of an integrated disease management approach for clubroot, and fully supports the recommendations of the Canola Council of Canada.

Falak and Christianson echo the sentiment. “All resistance traits will be effective for longer periods of time if they are used judiciously,” says Christianson. “Choosing resistant seed is only one part of a successful disease management strategy. Growers need to include crop rotation, field scouting and early detection of clubroot, and minimizing soil movement between fields on equipment.”

Falak agrees. He says following a proper canola rotation as well as rotation of resistance genes, combined with preventing soil movement and other agronomic measures “would enable sustainable clubroot management that would prolong efficacy of any new resistance sources that are introduced.”

 

How to Test Soils for the Clubroot Pathogen

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Soil tests for clubroot can have two objectives:

1. Is the clubroot pathogen present? (Yes/No test) This could be done with just one composite sample per field. Take samples (scoops) from higher-risk areas, such as field entrances, low spots or a water run that may bring resting spores into the field. For more refined results, send individual samples from each ‘hot spot’ to better understand the distribution of the pathogen within a field.

Farmers can use a ‘yes’ result to confirm that they should grow clubroot-resistant (CR) varieties. The general recommendation is to use CR varieties as soon as clubroot is found in the area (which are now most areas of the Prairies). A ‘yes’ result should also encourage heightened biosecurity and sanitation measures to keep clubroot from spreading within that field and to other fields.

Experience has shown that a positive result may not immediately lead to noticeable levels of clubroot. Resting spore levels could be too low for infection to be visible. Environmental conditions may not be conducive. Spores may not be viable. But soil tests can complement plant scouting practices for early detection of clubroot.

As a winter project, farmers could save the buckets of sampled soil and use it to grow canola plants to see if they produce galls. Remember, clubroot prefers moist and warm soil so keep the soil wet, but not saturated, and in a warm environment.

2. What is the resting spore count per gram of soil? (Quantitative test) In addition to the yes/no test, labs can also measure the amount of resting spores per gram of soil. Sample to a 15cm depth as spores in the top layer are most likely to cause yield-limiting infection. Quantitative results could be used to assess the clubroot risk level, but the ‘grey-area’ nature of this test creates problems for interpretation. Fewer spores mean lower risk, but clubroot infection can still occur at 1,000 spores per gram of soil, or less. If one field has 10,000 spores per gram and the neighbouring field has 100,000, both fields have a problem. And if a test shows 1,000,000 spores per gram, the field is clearly at risk and symptoms are likely to appear under most conditions.

Adding to the grey area is that results can be different depending on the lab (results cannot be compared lab to lab because of their different sampling, storage, extraction and analysis protocols) and the soil sampling location.

When sampling to determine the spore load in a heavily-infested area, collect samples from only that area as a composite sample from other areas may dilute the spore concentration. However, to get a fair estimate of spore load within a heavily-infested area, include soil from the canola row and from between the rows.

Eventually other objectives may be added – How many spores are actually viable and alive? What pathotypes are present and at what numbers? – which could be used to choose a variety with resistance to the predominant pathotypes in a field. This test for differing pathotypes, similar to the blackleg system, is not ready but significant progress has been made.

Source: Canola Watch

Clubroot Identified in Rocky View County Southeast of Calgary

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Clubroot has been identified in canola southeast of Calgary. Although clubroot has been found in various counties in Alberta since 2003, this is the first year the disease has been confirmed in Rocky View County.

This fall, southern Alberta canola growers should be especially diligent in scouting their canola fields for clubroot and should consider deploying resistant varieties in future canola production cycles.

Identifying clubroot as early as possible and keeping the pathogen’s spores from spreading are important steps in long-term clubroot management. With early detection, growers can take steps to contain and minimize spore loads and protect their fields. ANY method of soil movement can move the clubroot pathogen’s spores, such as tillage, dirt/dust on equipment and straw, wind or water erosion, and even animals.

Under high disease pressure, above-ground symptoms of clubroot can include stunted growth, wilting and premature ripening. These symptoms should not be mistaken for drought stress, which was common throughout southern Alberta this year. Start looking for the disease around field entrances and in areas with higher moisture or where soil movement may have occurred in a field’s history. Proper diagnosis should always include digging up plants to check for gall formation on roots. This time of year, many galls will likely have matured and decomposed into a peat-moss-like (or sawdust-like) substance around roots. If growers or agronomists find galls or a substance that looks like it might have been galls, samples can be sent to a lab for proper diagnosis. Find the labs list at clubroot.ca.

Source: Canola Watch

Clubroot Management: Harvest Theme

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Severe clubroot pulled from infested soil (note wilting of plants in the background). (Photo courtesy S.E. Strelkov, U of A)

Look. During harvest scouting, carefully examine the roots of unhealthy looking plants and also random plants chosen from around the field. Start in high risk areas, such as field approaches, then fan out in a “W” pattern. By this time of year, galls may start to break-down. Decaying galls will have a sawdust-like look and texture. If in doubt, send plant samples to a lab for identification. How to scout.

By this stage of the season, clubroot galls are starting to breakdown, leaving behind a sawdust-like material.

Test. Soil tests to determine if a field has clubroot could be done with just one or two composite samples taken from high-risk areas – like the field entrance or a water run that may bring spores into the field. Labs that do clubroot testing.

Clean. Moving soil means moving clubroot. Because more soil clings to machinery in wet conditions, wet harvests will increase the risk of clubroot movement on harvest machinery and trucks. How clubroot spreads.

Fields known to have clubroot could be done last to avoid spreading soil to other fields that do not have clubroot. Doing clubroot-infested fields last also means you’ll have more time to give equipment a thorough cleaning before bringing it home. If not doing those fields last, try to knock off as much mud and dust as possible before leaving the field and going to the next one.

(No) Tillage. Do not work infested fields when they are wet because more mud will stick to equipment and could be transported to clean fields. Note that fertilizer banding in the fall will move some soil. Growers will want to be conscious of clubroot when bringing in rented applicators and when NH3 nurse tanks are delivered. Perhaps clean the applicator before bringing it to the farm and take nurse tank deliveries at a fixed location at the edge of the field. When choosing a delivery location, perhaps avoid the main field entrance if possible since it will be one of the highest risk areas for potentially spreading clubroot to other fields.

Talk. If clubroot is found for the first time, report it to your neighbours and county or municipal office. As noted in discussions at the International Clubroot Workshop, people need to realize that clubroot is the “bad guy” here. Farmers who discover clubroot early and take action should be commended. Read our Top 10 from the ICW.

Source: Canola Watch

Scouting for Fusarium Head Blight Symptoms in a Developing Crop

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Premature bleaching of infected spikelet in wheat. Picture courtesy of Kelly Turkington, AAFC.

Scouting for fusarium head blight (FHB) symptoms is key to realizing whether a field is a candidate for the application of a FHB plan. Neil Whatley, crop specialist at the Alberta Ag-Info Centre, explains its importance and what to look for when scouting.

Fusarium head blight is a fungal disease of cereal crops that affects kernel development. “While caused by one or more species, Fusarium graminearum is considered the most important FHB species due to its aggressiveness and production of a toxin called deoxynivalenol (DON),” says Whatley. “This mycotoxin is a fungal chemical that affects livestock feed, the baking and milling quality of wheat, and the malting and brewing qualities of malt barley. Canadian Grain Commission grading standards allow very little tolerance of Fusarium damaged kernels (FDK) in the top grades of cereals.”

Whatley says that to limit the impact of FHB, grain producers must use a combination of disease management strategies throughout the growing season. “The first step in this strategy is realizing whether the disease is present in a developing crop by searching for disease symptoms. Additionally, learning whether Fusariumgraminearum is the dominant FHB species under observation and becoming aware of its prevalence and severity contribute to this first step toward potentially reducing its negative impact.”

FHB symptoms become visible in a cereal crop during the later heading stage. While disease infection takes place a few weeks prior at the flowering stage, symptoms appear when the plant reaches the late milk to early dough stage. “For spring seeded cereals, this typically occurs during the last part of July or early August,” explains Whatley. “Once symptoms are present, it is too late to apply a fungicide, however, this information is valuable for your FHB disease management plan in subsequent growing seasons.”

The most apparent FHB disease symptom in wheat is premature bleaching of one or more infected spikelets in the cereal plant’s head, which is visibly apparent on green heads. Orange, pink or salmon coloured fungal growth may also appear at the base and edges of the glumes on these blighted head parts. Symptoms in barley are much less distinct and the brownish discolouration of FHB infected barley spikelets can easily be confused with hail damage or the extended symptoms of other barley diseases like spot blotch, i.e. kernel smudge.

“If these symptoms are observed in a field, send the suspicious looking cereal head samples to a laboratory,” notes Whatley. “Several private seed company labs offer FHB testing services and the only way to confirm whether the affected heads contain FHB infection is to have them tested by a lab. Additionally, a lab test will determine whether the Fusarium species is indeed Fusarium graminearum or one of the less damaging fusarium species.”

Infection timing determines the severity of kernel damage. Explains Whatley, “While infection occurring at early flowering can lead to complete abortion of kernels, fusarium damaged kernels generally result from infection that occurs from the early to mid-flowering stages. Later infections that occur well after flowering and up to the soft dough stage of kernel development may not show visible symptoms. However, kernels may contain the fungus, and more importantly, the mycotoxin it produces.”

For more information about scouting for FHB symptoms, contact the Alberta Ag-Info Centre at 310-FARM (3276).

Source: Alberta Agriculture and Forestry

Increasing Numbers of Weeds are no Longer Responding to Herbicides

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Weed resistance to herbicides has been an issue in crop production for many years. However, it is is coming to the forefront as increasing numbers of weeds are no longer responding to herbicides.

“Most producers are aware of the issue but, unless it affects them directly, don’t see it as a huge issue,” says Harry Brook, crop specialist with Alberta Agriculture and Forestry. “For example, resistance to glyphosate – commonly known as RoundUp – is found in other parts of the world and Canada. We also now have glyphosate resistance in kochia in southern Alberta and it continues to spread. These should serve as a wake-up call to producers to the importance of rotating different herbicide groups when treating problem weeds. Failure to take this problem seriously will eventually result in the loss of our most popular weed control products.”

Herbicide resistant wild oats can be found in many field in the province. Some biotypes are resistant to more than one herbicide group.

“In Manitoba in 2016, 78 per cent of fields sampled had some group 1 resistant wild oats. The majority of herbicides used for wild oat control are in this group. If wild oats is resistant to a single herbicide in a chemical group, it’s pretty well resistant to all the herbicides that use that particular mode of action. Also in 2016, group 2 resistant wild oats was found in 43 per cent of Manitoba fields, and 42 per cent had wild oats resistant to both group 1 and 2. These numbers would be similar in Alberta. Soil-applied wild oat control is in group 8, which is older chemistry and has seen a resurgence in use. Cases of resistance to group 8 herbicides is increasing, despite it not being used much in the last 20 years.”

Cleavers, kochia, chickweed, spiny annual sow thistle, hemp nettle, green foxtail, wild mustard, smartweed, Russian thistle and stinkweed have all developed resistances to group 2 herbicides, says Brook. “That group contain the sulfonylureas, the “imi’s” and florasulam. Weed surveys from 2014 to 2017 estimate about 7.7 million acres or more in Alberta have some weed resistance issue.”

Brook says there are a few ways to detect a herbicide resistance issue. “Investigate areas in the field where weed control didn’t occur. Rule out other factors that might have affected herbicide performance including misapplication, spray misses, unfavourable weather conditions, and misapplication of herbicide at wrong leaf stage or late weed flushes. Other warning signs include other weeds listed on the herbicide being controlled adequately, patchy control with no reasonable explanation, a history of herbicide failure in the same area, lack of signs of herbicide injury on plants, and finally, a history of using the same herbicide group on the land, year after year.”

Brooks says when a producer uses the same herbicide or products using the same mode of action, they are actually helping select for those plants that are either not affected or affected less by the active ingredient than other plants. “By killing off susceptible plants, you are actually setting the stage for the resistant ones to thrive as all their competition is killed off.”

Herbicides that have one specific mode of action are most likely to develop resistant weeds. “Group 1 and group 2 herbicides fall into this category,” says Brook. “However, the most important reason for having resistance show up is due to repeated use of the same chemical. Short crop rotations and a lack of crop variety has set up the conditions to encourage weed resistance to emerge.”

Canada has reported resistance issues in weeds to at least six different herbicide groups. “If we ignore the risk of developing resistances, the day may come when we might lose some of our best herbicide tools from the weed management tool box. Pay attention. Scout your fields. Keep field records. Use a good crop and herbicide group rotation to keep this problem at bay. The consequences of not doing so are not cheap or pretty.”

For more information about herbicide resistance, contact the Alberta Ag-Info Centre at 310-FARM (3276).

Source: Alberta Agriculture and Forestry

Clubbing Clubroot

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Photo: Janet Kanters

On the Prairies, clubroot appeared in Alberta in 2003, in Saskatchewan in 2008 and Manitoba in 2013. As any grower can tell you, it’s a nasty canola disease that usually worsens in a field every year, partly because the spores are very easy to spread and so hardy they can survive for up to two decades in the soil. Combine this fact with the strong prices that canola fetches these days – widely encouraging back-to-back or two-year rotations – and you have a big problem.

Companies are certainly moving as quickly as possible to produce seed with effective resistance to clubroot, but breeding to defend against this particular pathogen involves navigating a wide range of complex challenges.

“Clubroot has a very short lifecycle resulting in several generations per season,” explains Dr. Marcus Weidler, vice president of seed operations at Bayer CropScience, “enabling the pathogen to react to changes in its environment very quickly, including new crop resistance genes.”

Dr. Jed Christianson, pathology lead at Monsanto Canada, explains that clubroot’s large and quickly-adapting population sizes means that it takes relatively long canola rotations of three or four years to see significant drops in the number of viable spores in the soil, and very long rotations of over 10 years for spores to effectively disappear.

“Each gall produced on a canola root can contain billions of spores,” he says. “So, given the numbers of spores generated, even very rare events like the emergence of individual spores that have gained the ability to infect resistant canola will happen over a fairly short number of cropping cycles. A one in a billion event doesn’t seem that unlikely to happen when you’re given 20 billion chances.”

Combine this with the fact not all clubroot pathotypes (races) have been identified, and it’s therefore difficult, explains Weidler, to develop a canola variety that is resistant to all potential pathotypes to which a plant may be exposed.

Dr. Igor Falak reminds us that it was in 2013 that a new clubroot pathotype was identified, one to which all canola varieties on the market carrying resistance to the original 2003 pathotype were susceptible. Although hybrids with the initial type of resistance continue to hold their own on most infested acres, the number of fields with the new pathotype is increasing annually. Falak, senior research scientist with Corteva Agriscience, blames this situation on “years of canola-on-canola.”

In addition, he notes that although clubroot “is similar to another disease of canola (blackleg), where canola products may carry race specific resistance,” clubroot-resistant canola varieties “do not have ‘fallback’ resistance mechanisms, unlike blackleg-resistant products that also have a different type of stable resistance.”

More breeding challenges are found in the fact that because canola plants carry no clubroot resistance genes, all the major seed companies are actively testing resistance genes found in rutabaga, cabbage and turnip. However, Weidler notes that because these species are only remotely related to canola, it’s far from easy to transfer genes between them without also transferring additional unwanted genetic “baggage” that negatively impacts yield, canola quality or agronomics.

If all this wasn’t enough, clubroot is a challenging organism to deal with, having unique characteristics – described by Weidler as a form of life “somewhere between a bacterium and a fungus.”

Christianson concludes that the biggest challenge in creating clubroot-resistant canola seed is to introduce resistance “while continuing to improve hybrid performance for yield, maturity, standability, resistance to other diseases, harvestability, seed quality and all of the other attributes that are important to growers’ success.”

Breeding Steps to Develop Clubroot-Resistant Canola Seed

Christianson says the steps involved in breeding clubroot-resistant varieties are relatively simple, and that any breakthroughs relating to resistance genes “are really just the discovery and characterization of more of them through concerted screening efforts.”

The entire process is a matter of crossbreeding canola with resistant relatives through normal pollination procedures and recovering offspring that are clubroot-resistant. “Those offspring then have to be crossed with canola again and again through many generations, selecting the resistant offspring at each generation for use in the next cycle to obtain plants that maintain resistance, but have recovered the characteristics of high-performing canola,” Christianson explains.

Weidler adds that unwanted genetic material from the resistance donor that negatively impacts the agronomic performance of the offspring is removed through several crossings of the offspring with elite parent stock. “Using molecular breeding tools, we can check the progress towards the end goal,” he notes. “Ideally, only the genetic sequence conferring clubroot resistance has been transferred and no other parts of the donor genome remain in the offspring.”

Breeding Progress

DowDupont was the first company in Canada to market clubroot resistant hybrids in 2009 (45H29).

“Our hybrids have multi-source and multi-race resistance to clubroot, and have a high level of resistance to the most prevalent clubroot race – race 3 – along with resistance to races 2, 5, 6 and 8,” Falak notes. “We have five hybrids with clubroot resistance: 45H29, 45H33, 45CS40, 45CM36 and 45H37. Pioneer hybrid 45CM36 is one of our newest products that contains a new source of clubroot resistance that confers resistance to both the initial type and new pathotypes, and can be rotated with the original resistant hybrids.”

Hybrid 45CM36 was launched in 2017 and is widely available to western Canadian famers for the 2018 growing season.

For its part, Bayer CropScience has “identified several new potential resistance sources,” says Weidler, “and we have been able to demonstrate that these are different from what is currently on the market.”

Christianson says that as Monsanto nears “actual commercial entry into the marketplace, we will have more to share about how second-generation resistance fits in with existing resistance traits to provide a sound disease management strategy.”

No matter what resistant canola varieties are marketed, no company can predict how long a new variety will last before it’s compromised. This depends on too many factors, explains Weidler, including the resistance gene, environmental conditions and management practices.

All the companies strongly agree that the existence of varieties with resistance is only part of the clubroot solution.

Weidler emphasizes the importance of an integrated disease management approach for clubroot, and fully supports the recommendations of the Canola Council of Canada.

Falak and Christianson echo the sentiment. “All resistance traits will be effective for longer periods of time if they are used judiciously,” says Christianson. “Choosing resistant seed is only one part of a successful disease management strategy. Growers need to include crop rotation, field scouting and early detection of clubroot, and minimizing soil movement between fields on equipment.”

Falak agrees. He says following a proper canola rotation as well as rotation of resistance genes, combined with preventing soil movement and other agronomic measures “would enable sustainable clubroot management that would prolong efficacy of any new resistance sources that are introduced.”

Pioneering work on Fusarium head blight in rye

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Based on the study's preliminary results, some rye lines, like the one shown here, are susceptible to Fusarium head blight, but most are in the resistant to intermediate range. (Photo: Duoduo Wang, University of Manitoba)

Unlike other cereal crops affected by Fusarium head blight (FHB), very little is known about FHB in fall rye from a Canadian perspective. We don’t know how serious a concern FHB might be in our rye crops. We don’t know which Fusarium species are infecting rye. We don’t have FHB ratings for our current rye varieties. And we have limited information on optimal timing for fungicide applications to manage FHB in rye.

So Jamie Larsen with Agriculture and Agri-Food Canada (AAFC) at Lethbridge and Anita Brûlé-Babel with the University of Manitoba have teamed up on a project to develop FHB-related information and tools that rye growers need.

“This research is new territory from a Canadian and even a North American perspective,” says Larsen, who has breeding programs for open-pollinated fall rye and several other cereals.

“Rye has not had a lot of attention from Canadian researchers and growers for a very long time. But the playing field has changed with the new rye hybrids. They are significantly higher yielding, they are shorter, and they are easier to harvest. So now there is renewed interest in rye,” notes Brûlé-Babel. “It’s important to get a sense of how rye responds to Fusarium head blight and whether there is going to be an issue with the disease and what rye growers should do in conditions where Fusarium is a concern.”

Larsen became interested in the issue due to several factors that have emerged in recent years. “Initially when I started working in rye, I had looked at the literature and I thought the disease wasn’t a major problem. Also, the main areas where rye is traditionally grown – north of Swift Current and around the Great Sand Hills area in Saskatchewan – aren’t huge Fusarium head blight areas. And rye has this natural ability to be tolerant to a lot of diseases. So I wasn’t too worried about Fusarium head blight,” he explains.

“But then I sent some rye varieties to Ontario as checks in a triticale experiment. And as I was walking along in those plots, I saw a rye variety with its head completely glued shut and pink with Fusarium. I’d never seen anything like it.” As well, he found out FHB occurs in Prairie rye crops through his work as the coordinator for the fall rye cooperative registration trial. Each year, the trial is grown at 15 locations across Western Canada, and in some years Fusarium-damaged kernels (FDK) have been found in the grain samples from the trials.

Another driver for Larsen was the potential, especially with the new hybrids, to sell more rye into the feed and food markets. To help in realizing that potential, he saw the need to know more about FHB’s impacts on rye yield and quality – particularly since Fusarium species can release toxins that can limit the use of grain in feed and food – and the need to develop FHB-resistant rye varieties and other tools to manage the disease.

FHB is not common in the Lethbridge area, but it is a widespread concern in Manitoba, and Brûlé-Babel conducts screening for FHB resistance as part of her winter wheat breeding program. So Brûlé-Babel and Larsen brought together their different areas of expertise to develop their plans for the project. Also joining the project is KWS, the German company that has developed several hybrid ryes for Canadian growers.

Evaluating Rye Lines for Resistance

Brûlé-Babel is screening fall rye lines for FHB resistance at her FHB nurseries at Winnipeg and Carman. To increase the potential for disease development, her research team inoculates the rye lines with Fusarium graminearum, the most common of several Fusarium species that cause FHB in Manitoba cereals.

The FHB responses of the rye lines are measured in three ways: disease levels in the field; FDK levels in the grain; and concentrations in the grain of deoxynivalenol (DON), the primary toxin produced by Fusarium graminearum.

In 2017, they evaluated about 70 rye lines, including materials from Canada, the United States, Germany, Russia and other countries, as well as lines from Larsen’s breeding program and from KWS. Current Canadian rye cultivars are included in the screening so growers will be able to get information on FHB ratings to help in choosing rye varieties for their farms. For 2018, the researchers have added more rye lines from KWS, so the total is now about 130 lines.

The 2017 results showed that FHB definitely occurs in rye and that some lines are more resistant than others.

“Overall, we’re not seeing very many lines that are as susceptible as our susceptible wheat checks. And most of the rye lines are in the resistant to intermediate range,” notes Brûlé-Babel.

The testing for FDK and DON in the 2017 samples will be done in the coming months by KWS. However, based on what Brûlé-Babel’s team observed in the field and as the grain samples were harvested, it appears that FHB infection often tends to cause the rye plant not to set seed. As a result, the FDK levels are lower than would be expected in a wheat crop with similar field infection levels.

Brûlé-Babel had heard anecdotally through their KWS collaborators that DON levels in rye tend to be quite low. She suspects this could turn out to be true if there aren’t many infected kernels in the harvested grain to contribute to DON in the samples.

“So my guess at this point is that the biggest problem from Fusarium head blight for rye producers might turn out to be yield loss as opposed to a crop that you can’t market [due to FDK and DON],” she says.

Once they have two years of data from the nurseries, Larsen will start making crosses with some of the FHB-resistant lines so he can develop new open-pollinated varieties with this trait.

Other Fusarium Species

Brûlé-Babel is also leading two other FHB/rye studies for the project. One study is looking into other Fusarium species that cause FHB in rye. “Not a lot is known about which Fusarium species infect rye [on the Prairies], so we’ve worked with Maria Antonia Henriquez at AAFC’s Morden Research and Development Centre. She does a Fusarium survey every year, collecting diseased plants from [spring wheat and winter wheat fields in Manitoba]. So we asked if she could also collect samples from rye fields,” explains Brûlé-Babel.

One of Brûlé-Babel’s graduate students, Duoduo Wang, has isolated the Fusarium species from the Manitoba rye samples. Wang has identified the species based on the appearance of the fungi when grown in the lab, and she will be doing some DNA marker work to confirm the identifications. The preliminary results indicate that the most common species was Fusarium graminearum, but other species were also present.

In 2018, Wang will be doing a greenhouse study to examine the infection process and see how the different Fusarium species interact with selected rye cultivars.

Optimizing Fungicide Timing

Wang is also working on the other study, which is investigating fungicide timing for managing FHB in rye. “Very little information is available on fungicide timing for rye for this disease. We need to develop some basis for timing recommendations,” says Brûlé-Babel.

According to Larsen, the general recommendation for fungicide timing for FHB in wheat is to spray two days after heading because wheat plants usually flower about two days after heading. But in rye, flowering might not start until seven to 14 days after heading. In that long heading/flowering period, what is the best time to apply a fungicide?

Brûlé-Babel also points out that, because rye is an outcrossing species, its florets are open for a longer period than the florets of a self-pollinating species like wheat, and it may be that a fungicide might interfere with pollination and seed set in rye.

From the rye lines being screened in the nursery, Wang has selected an FHB-susceptible cultivar, a cultivar with an intermediate response, and an FHB-resistant cultivar to use in the fungicide trials. The trials will take place at Winnipeg and Carman. The fungicide will be Prosaro, a commonly used fungicide that is registered for FHB suppression in wheat and barley.

The trials will compare four fungicide timings: at 50 per cent heading; at 10 per cent anthesis, which is when 10 per cent of the flowers on the spike have extruded anthers; at 80 per cent anthesis; and at six days after flowering. Brûlé-Babel’s team will be inoculating the plants with Fusarium graminearum. The trials will also have two types of check plots: inoculated with no fungicide and non-inoculated with no fungicide.

Larsen hopes they’ll be able to figure out an easy-to-use general rule for FHB fungicide timing in rye similar to the two-days-after-heading guideline for wheat. He adds, “The hybrids are typically a lot more uniform in flowering timing than the open-pollinated ryes, so fungicide timing for open-pollinated ryes might turn out to be a little trickier.”

Practical Results

This pioneering project will lead to practical information, improved varieties and other tools for rye growers in Western Canada and perhaps other regions of the country.

“Providing good information for farmers to make decisions is very important. Part of the reason we’re doing this research is to make sure there won’t be any surprises in terms of potential Fusarium problems for rye growers,” Brûlé-Babel says. “I’m quite excited about the revival of interest in rye because it’s a very good crop for many uses and definitely contributes to diversification on the landscape.”

This FHB research is part of a larger project led by Larsen on rye disease issues that also includes work on ergot and rust. Saskatchewan’s Agriculture Development Fund, Western Grains Research Foundation, Western Winter Wheat Initiative, Saskatchewan Winter Cereals Development Commission, FP Genetics, KWS and Bayer CropScience are funding the project.

VIEWPOINT: Learning to live with Fusarium

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Alberta’s Fusarium Management Plan, developed to limit mycotoxin production and subsequent grain contamination, and to prevent the spread of Fusarium graminearum into Alberta was a good idea – at the time it was implemented. But now that Fusarium is established in Alberta, growers need to take matters into their own hands to mitigate the effects of this serious disease of cereals. Alberta Seed Guide spoke with Kevin Auch, chair of the Alberta Wheat Commission and a farmer in the Carmangay area, about the issue and what farmers can do to diminish the chance of Fusarium appearing in their fields.

Alberta Seed Guide: Fusarium head blight is top of mind for Alberta cereal seed growers and farmers. Why is this specific disease such a threat?

Kevin Auch

Kevin Auch: Fusarium is a severe downgrading factor for wheat and its slow creep into Alberta has the potential to severely affect wheat production here. The disease is adversely affecting wheat production in other provinces where it is prevalent, and is curbing wheat profitability and production. For example, durum used to be a popular crop in Manitoba, but since durum is more susceptible to Fusarium than other wheats, the prevalence of Fusarium in Manitoba has virtually eliminated durum production in that province.
ASG: The Alberta Fusarium graminearum Management Plan has been in place since 2002, to “limit the introduction, escalation, spread and economic impact of F. graminearum in Alberta.” Is the plan doing what it set out to do? Why or why not?

KA: I think the Alberta Fusarium graminearum Management Plan was reasonably effective at slowing the introduction of the disease into Alberta. But now that the disease is here, and seed is no longer the main threat or source of transmission of the disease, it is becoming more apparent that other alternative strategies may now need to be employed.
ASG: Currently, Fusarium graminearum (Fg) is listed as a pest in the Alberta Agricultural Pests Act, and no person or company can sell​, transport​ or plant infected seed. ​Are most farmers testing their seed or purchasing tested seed to know that it is Fg free? ​

KA: I think a good percentage of farmers are testing, and it makes sense for farmers to plant the best quality seed possible. However, to enforce zero per cent Fusarium seed limits on a farmer who already has Fusarium in the fields he is planting doesn’t make too much sense anymore. While higher germination seed is better, we don’t enforce the use of 100 per cent germination seed; and in a case like this one where a farm already has Fusarium, zero per cent Fusarium seed doesn’t make sense either.
ASG: With the spread of Fusarium throughout the province, the access to disease-free seed is limited. How can Alberta farmers overcome this challenge?

KA: Properly applied seed treatments are one of the best management practices that can help control the spread of the disease, and protect seedlings from other diseases as well.
ASG: Why is changing the Pests Act important in the management of Fusarium now and into the future?

KA: Currently the way the legislation is written, it’s illegal to plant anything but disease-free seed. But proper seed treatment of wheat that is going into fields that already contain low levels of Fusarium may be a better management practice.
ASG: Until changes are made, what can the ​crop industry and farmers do to mitigate Fusarium, now and into the future?

KA: I can’t stress enough the importance of adhering to best management practices that help slow the spread of the disease and properly using all the tools available to us.

Combination of resistance genes offers better protection for wheat against powdery mildew

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Wheat line without Pm3 alleles, infected by powdery mildew. (Photo: UZH)

University of Zurich (UZH) plant researchers have tested newly developed wheat lines with improved resistance to powdery mildew in field trials. They have demonstrated that a combination of two variations of a resistance gene provides wheat with better protection against the fungal disease.

For several years now, UZH researchers have been investigating a wheat gene that confers resistance to powdery mildew (Blumeria graminis f. sp. tritici). The gene, called the Pm3 resistance gene, exists in different variations, so called alleles. In previous studies, plant researcher Beat Keller and his team demonstrated that single Pm3 alleles are able to confer resistance against powdery mildew fungi. And yet, a single resistance gene can quickly lose its effectiveness. Thus when it comes to plant breeding, it is important to combine multiple resistance genes. This is exactly what researchers at UZH have now tested in field trials using transgenic wheat lines.

The researchers created new wheat lines by crossbreeding transgenic Pm3 lines. This resulted in four new wheat lines, each containing two different Pm3 gene variations. “These four new wheat lines showed improved resistance against powdery mildew in field trials compared with their parental lines – during the field seasons 2015 to 2017,” explains Teresa Koller, lead author of the study.

Back in the laboratory, the scientists proved that the parental lines’ gene activity is added up in the newly created lines. Each Pm3 allele in the four new lines displayed the same activity as in the parental line, which results in increased overall activity, since it came from two different gene variations. “The improved resistance against powdery mildew is the result of the increased total transgene activity as well as the combination of the two Pm3 gene variations,” summarizes Teresa Koller. The high overall activity of resistance genes did not cause any negative effects for the development of the wheat or its yield.

The findings of these trials improve our general knowledge of the immune system of plants, and in particular of fungal disease resistance of wheat. Besides contributing to fundamental research in the area of plants’ immune systems, the findings can also be applied in wheat breeding. Thanks to the precise testing of Pm3 alleles, the best variations and combinations are identified and can then be used directly in traditional breeding by crossbreeding them into modern wheat varieties.