Long days, cold nights, short seasons
By Carolyn King
Identifying soybean varieties suited to tough Prairie growing conditions
As soybean production spreads west and north across the Prairies, the growing conditions become more and more challenging for this plant, which originated in the subtropics. Canadian researchers are working to advance soybean production under these tough conditions. A key element in this research effort is a project to evaluate registered soybean varieties and find ones that can perform well in these very-far-from-subtropical conditions.
“First of all, soybeans are not usually adapted to cold conditions. Secondly, soybeans evolved as short-day plants, maturing much faster under short-day conditions. When we move them to more northerly latitudes with longer hours of daylight in the summer, their maturity date is delayed. For instance, a variety that is suited to Kentucky would mature 30 or 40 days later in Ontario,” explains Leonid Savitch, a research scientist with Agriculture and Agri-Food Canada (AAFC) in Ottawa who is leading this project.
“Our breeders are producing early-maturing varieties that are capable of withstanding long days and still maturing in time. Those varieties work perfectly well in Ontario or Quebec conditions. But when we try to grow them in Western Canada, some of them perform decently, and some of them are not acceptable at all, even though all of them are designed for a longer daylength. As soon as cold temperatures are applied, some varieties will have a delay in maturity by 50 or 60 days.”
Cold temperatures during the day and night can reduce photosynthesis, delay reproductive development and lower productivity in soybeans.
Temperatures that are only cold at night are also a problem. “For example, in Saskatchewan, you might have 30 C during the day and then 5 C at night,” he says. “Those cold night temperatures tend to cause soybean plants to drop flowers, produce much smaller yields and have undesirable changes in seed composition.”
In this project, Savitch and his team are characterizing and assessing early maturing, non-genetically modified (non-GM) soybean varieties developed by Elroy Cober, the soybean breeder at AAFC-Ottawa.
Savitch explains that Cober’s breeding program is set up to not directly compete with commercial soybean breeding programs that target GM varieties. He also points out that there is a nice niche market for non-GM soybeans because a number of countries do not accept GM soybeans.
Interesting progress so far
Savitch’s current five-year project started in 2018, but it builds on his previous research on this topic. Savitch and his team have developed a set of temperature and daylength regimes that they use in controlled environment chambers.
These regimes can differentiate the soybean germplasm into three groups based on the phenotypic responses of the plants. “Some of the plants will behave really well under the so-called stress conditions, predicting that they will be okay in Saskatchewan. Some of them will produce the same yield, but the seed quality will be extremely poor. And some of them might delay flowering and maturity by about two months,” he explains. “The varieties in first group are probably the best candidates for Saskatchewan.”
Over the past two and a half years, Savitch’s team has evaluated over 40 of Cober’s varieties.
Although this controlled environment evaluation method is effective in identifying which varieties are promising and which ones aren’t, it is very time-consuming. The plants have to been grown to full maturity, and some of the varieties can take as long as five months to mature under certain regimes.
Therefore, Savitch and his team are also trying to develop screening tools that could be used to differentiate the three phenotypes at an earlier plant growth stage. They are conducting multiple biochemical experiments and measuring photosynthesis, chlorophyll accumulation or degradation, water-use efficiency and other mechanisms related to growth, flowering and yield formation that can be affected by cold temperatures. Then they will determine which of these factors have the strongest correlations with the results from the full-length controlled environment tests.
In another component of the project, Savitch is collaborating with Tom Warkentin and Rosalind Bueckert, who are both professors at the University of Saskatchewan. Warkentin and Bueckert are field testing the varieties assessed by Savitch’s team.
Savitch explains that it is critical to see how the varieties perform in the field because, in a controlled environment, it is difficult to exactly reproduce the natural pattern of increasing and then decreasing daylengths over the growing season.
He adds, “We know from other research and our own controlled environment experiments that soybean varieties bred for early maturity under long day conditions will have delayed flowering and maturity if low temperatures are also applied. But if we put those same plants on a short day, there is no effect of cold temperatures on the plants.”
This delayed flowering and maturity may be the effect of low temperatures alone, but the project’s initial findings seem to indicate that long daylengths and low temperatures may have a combinatorial impact on soybeans. “We have to look into this a little more, but it gives us some extra ideas about where to go next in our research,” Savitch says.
The four Saskatchewan sites include irrigated and non-irrigated sites, as well as different soil types and weather conditions.
The field tests involve all the varieties evaluated by Savitch’s team, whether or not the varieties were identified as promising in the controlled environment experiments. This allows the researchers to determine how well the field results align with the controlled environment results.
So far, the field results are showing that Savitch and his team are on the right track with their controlled environment evaluation methods.
The field tests assessed 24 varieties in 2019 and 48 varieties in 2020 at the four locations, with replicated plots at each location. Some of the 2020 trials will likely be repeated in 2021 because an early September frost killed quite a few of the plants.
One of the interesting observations from the irrigated versus non-irrigated sites is that drought stress may make the impacts of cold stress even worse.
“Under irrigation, the effect of low temperature is less severe,” Savitch says. “So in the future, we will probably want to look at a combination of both low temperature and drought because both factors will delay flowering and maturity.”
For crop growers, an immediate benefit from the project will be identification of non-GM soybean varieties that produce better yields and better seed quality under western Canadian conditions, which would help Prairie growers to successfully compete in non-GM markets.
The project’s results could also help in the development of new soybean varieties for the Prairies. For instance, the top-performing varieties in the project could be of interest to breeders as possible parents for their crosses.
The screening tools developed for the project could also be helpful to breeders developing soybeans for the Prairies, whether their programs focus on GM or non-GM lines.
In addition, the findings from the project’s experiments and measurements to develop these screening tools could increase scientific understanding of the mechanisms and regulation of soybean cold stress tolerance and cold-induced effects on photosynthesis, flowering, maturity, yield and quality.
That increased understanding could help towards development of DNA markers related to these characteristics. And those markers would be an even easier way to screen breeding lines for adaptation to Prairie conditions.
Savitch concludes, “This industry-driven project is linking our controlled environment studies to the actual conditions where Saskatchewan growers are proposing to grow this crop.” By drawing on expertise at AAFC in Ottawa and the University of Saskatchewan, the researchers are striving to advance Prairie soybean production.
This project is funded under the Soybean Cluster, which is supported by the Canadian Field Crop Research Alliance (a collaboration of provincial crop grower groups and industry partners) and AAFC’s Canadian Agricultural Partnership.
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