Getting to the Root of Root Rot Problem in Saskatchewan - PulseResearch
April 24, 2017
Research dollars uncovering new ways to deal with root rots
In November 2015, Saskatchewan Pulse Growers (SPG) held a meeting to determine how to focus agronomic research priorities going forward.
The number one concern that came forward from growers and agronomists at the meeting was Aphanomyces and/or root rot complex diseases.
This was not a surprise, says SPG’s Agronomy and Seed Program Manager Sherrilyn Phelps.
“In 2015 we really did not have too many root rot issues, but there were a lot of people still dealing with it from 2014, so it is still forefront in their minds,” she says. “They have seen the devastation that can result under the right conditions.”
Although other countries, such as France and the United Kingdom, have been dealing with Aphanomyces for decades, it is a relatively new problem to the Canadian prairies, resulting from unusual weather conditions, Phelps says.
“We have just had the perfect storm for this disease to develop in our area,” she says. “In the past five to six years we had consistent wet conditions across the province, so when peas were seeded in 2010 and then again in 2014, the organism was able to survive and multiply in the first pea year, and in the second pea crop it was just devastating.”
Since Aphanomyces is relatively new to the Canadian Prairies, there are few effective management techniques to control the disease, even though there are seed treatments available for control of other root rot pathogens such as Fusarium, Rhizoctonia, and Pythium. Some crop protection companies have said they are working on seed treatments for Aphanomyces but there has not been a silver bullet yet.
Currently growers are advised to monitor their crops and if root rot is suspected, to send root or soil samples to a diagnostic lab for testing. If Aphanomyces is detected and the field shows uniform root rot symptoms, growers are advised to wait at least six years before planting peas or lentils, as the disease remains in the soil for a long time.
Therefore, Aphanomyces root rot continues to pose a huge risk to lentil and pea production in terms of acres and yield potential in the future, especially if environmental conditions continue to be on the wetter side during spring and early summer, Phelps says.
This is why SPG’s research investments around the disease are currently focused on three main components, which aim to diversify the management options for this devastating disease:
- Developing resistant varieties,
- mastering early detection techniques, and
- determining agronomic best practices to manage the disease.
It is Complicated
Adding to the existing challenge of managing Aphanomyces is its relation to root rot, which is complicated, says Dale Risula, Provincial Specialist of Special Crops with the Saskatchewan Ministry of Agriculture.
“Root rots are not just caused by one organism and that is why they are so hard to control,” he says.
“Often there is more than one pathogen involved and that is why it is often referred to as a root rot complex.”
Furthermore, with root rots, pathogens can infect the plants at any time during the lifecycle, he says. “The pathogen invades the roots, often near the seed, and infection spreads throughout the underground portion of the plant. Above-ground symptoms take time to appear and by the time you see the above-ground symptoms it is often too late.”
Early infections are the most devastating in terms of yield loss, as the infection starts at the seedling stage before any yield is set. Infections can also occur later in the season and may not show up in yield loss or symptoms above ground.
“However, the stem is weakened and will lodge prior to harvest making harvesting difficult,” Risula says. “These are the fields that go flat to the ground.”
It is interesting to note this disease only affects peas and lentils. Chickpeas, soybeans, and faba beans all have good partial resistance and with dry beans, it depends on the variety.
Developing Resistant Varieties
Dr. Sabine Banniza, a Plant Pathologist at the Crop Development Centre and a Professor of Plant Sciences at the University of Saskatchewan, has been working on developing Aphanomyces-resistant varieties of peas and lentils.
More specifically, Banniza is the lead on two major Aphanomyces-related projects, both funded by SPG and both aiming to speed up resistant variety development through rapid generation technology (RGT), which accelerates seed germination, reducing the time to flowering and eliminating the seed maturation and desiccation period. For lentils, RGT has proven very effective, resulting in the production of five generations of Saskatchewan varieties per year.
Banniza’s first project aims to identify both the strain of the pathogen of Aphanomyces in Saskatchewan as well as germplasm with high resistance and then integrate this resistance with RGT technology.
To carry this out, Banniza and her team began collecting soil samples from pea and lentil fields in Saskatchewan last year and have been isolating strains of the pathogen that will be characterized to determine what pathotypes they are. Preliminary screening with a Saskatchewan strain of Aphanomyces has already drawn a few conclusions, including that wild pea does not appear to have resistance, and that all cultivated lentil samples were susceptible.
The team is also currently working to develop a system that will intensify screening in order to identify additional sources of resistance that can then be integrated into RGT protocols.
As partially resistant germplasm has already been developed in France and the United States, Banniza’s research will also be able to borrow from some of this research to help guide the screening and selection process for peas for Saskatchewan.
“We have the advantage of other scientists having done the groundwork,” Banniza says.
The second project Banniza is leading focuses on developing RGT for wild lentil crosses, as there is indication that they may have partial resistance to the pathogen. Although the technology has been successfully developed and is being used for cultivated lentil varieties, it had never been tested on wild lentil and crosses involving wild species.
“Wild seeds naturally have slow and uneven germination due to differences in dormancy rates enabling these species to survive in the wild,” Banniza says. “Having compounds that would inhibit one of the plant hormones involved in seed dormancy could overcome dormancy issues and greatly improve and speed up RGT in wild, as well as cultivated lentils.”
Through this research the team was able to determine changes that could be made to the environmental growing conditions of the plants rather than hormonal manipulations, which resulted in seeds germinating much faster. This development translated into a substantially accelerated timeline for moving wild lentils through a single lifecycle from planted seed to harvested seed.
“For growers this means that new varieties will be available one year faster than using conventional methods,” Banniza says.
And although we are at least 5-6 years out from having pea varieties with built-in resistance to Aphanomyces (and longer for lentils), these research findings are the small, but necessary steps that take us closer to the ultimate goal.
In areas of the world most affected by Aphanomyces root rot, soil indexing tests are a recommended practice to help avoid the disease. For example, in France, a quantitative DNA test was recently developed that helps predict root rot risk. These types of tests allow growers to assess the risk in their fields and then use this information to limit the short- and long-term impact of this disease.
To develop such a test for Saskatchewan, local growing conditions and production practices would have to be incorporated, says Syama Chatterton, a Research Scientist at Agriculture and Agri-Food Canada’s Lethbridge Research and Development Centre.
“We first need to determine how oospore inoculum levels relate to disease severity levels in the different soil types common in Saskatchewan,” she says.
In order to help fill in these gaps, Chatterton is leading research, funded by SPG, which aims to develop an infection model for soil zones which would outline how the disease evolves in different soil zones, how the different species and pathogens interact, and how seed treatments affect the disease.
Chatterton began by conducting a mass survey of root rot in field peas in 2013 and 2014, examining the severity and variation of the disease and its pathogens across Brown, Dark Brown, and Black soil zones in Saskatchewan. Those samples are now being used in trials that compare the response of root rot to inoculum.
So far the trials have yielded a few preliminary results. For example, it appears that Dark Brown soils are the most conducive to disease development and the presence of other soilborne pathogens has a synergistic effect on disease development by Aphanomyces.
Chatterton’s research also saw her team surveying Saskatchewan fields in 2015. This phase of the research was able to give an idea of the occurrence of the disease and its relation to root rot and pathogens. Of the pea fields surveyed in Saskatchewan in 2015, 50 per cent of them tested positive for the presence of Aphanomyces and from those positive fields, on average 58 per cent of root samples tested positive for the disease.
“We also found that Fusarium was present in every field surveyed, and Fusarium avenaceum and Fusarium solani were the most common,” Chatterton says. “These fusarium species are not as virulent or aggressive at causing root rot as Aphanomyces euteiches, but our observations suggest that the presence of both Aphanomyces and Fusarium avenaceum or Fusarium solani results in the most damage to roots.”
Another round of trials will happen next year to ensure results are consistent within soil types and not due to field location, but Chatterton already feels the study has made progress towards larger goals.
“Results from the first year of this project suggest that quantification of Aphanomyces euteiches inoculum levels in field soil samples can be used to predict risk levels of Aphanomyces root rot, and represent the first step in achieving the goal of developing a quantitative DNA test to predict root rot risk,” she says.
Agronomic Best Practices
Although SPG-funded research aims to develop tools that will be used in agronomic best practices, it is still too early for any conclusions that will aid growers in coming years, and it will likely be years before any resistant lentil varieties are developed.
For now, SPG research will prioritize studying agronomic practices such as the effect of seed treatment, tillage, foliar applications, and the effect of herbicides on pre-emergence.
“We are looking to see if we can improve tolerance and reduce stresses so that the plant is healthier and better able to fight off disease,” Phelps says.
Another area that is currently being studied is the effect of the disease on growing other pulses such as chickpeas, soybeans, and faba beans in rotations.
“You may be limited to growing peas and lentils once in six to eight years, but does that mean you cannot grow chickpeas, soybeans, or faba beans? We are evaluating these questions now,” Phelps says.
For now the advice to growers is the same — avoid planting peas and lentils on fields that have been identified as positive for Aphanomyces, and always ensure the health and vigour of seedlings, Phelps says.
“Good seed, seed treatments where necessary, seeding into nice warm soil, making sure nutrient levels are appropriate, and minimizing other stresses that might make plants more susceptible to root rots — these are all recommended practices,” Phelps says.
For a list of ongoing SPG-funded research in this area, download the magazine.