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Breeding for rotational synergies

Developing high-yielding lentil and wheat varieties that work even better together.

June 14, 2024  By Carolyn King


As part of this project, greenhouse experiments will be tracking the nitrogen fixed by the lentil plants to see how much is taken up by the durum plants. Image courtesy of Kirstin Bett, University of Saskatchewan

Recently, when University of Saskatchewan researchers Kirstin Bett and Curtis Pozniak were chatting over coffee, they came to a realization that is both off-the-wall and obvious – and has important implications for sustainability.

“We were talking about the concept that producers follow crop rotations to manage diseases, weeds, and nutrients, but breeders breed their crop on its own, without really thinking about the consequences for the next crop in the rotation,” says Bett, a professor of pulse crop genomics and dry bean breeding at USask’s Crop Development Centre (CDC).

“We realized we need to be breeding varieties for a rotational production system – as well as breeding to maximize yield and productivity of the individual crops,” says Pozniak, a professor of wheat genetics and breeding, and CDC director.

So, the pair have initiated an innovative research project to work on this idea. The project involves selecting lentil and durum lines for synergistic interactions in rotation, focusing on combinations that enhance nitrogen-use efficiencies in the rotation.

As Bett explains, “We want to see if it is possible to come up with a realistic way of making selections for lentils that are not only great lentils but are also going to be especially good for the subsequent durum wheat crop, and selecting durum lines that are great durum wheats and are also really good at taking advantage of being grown after a lentil crop.”

Multi-species genomic breeding
The team built on an approach used in a small proof-of-concept trial conducted about 15 years ago by other CDC pulse and cereal breeders. That trial compared about a dozen lines of a pulse crop followed by about a dozen lines of a cereal.

Those results showed the yield response of the cereal lines did indeed depend on which particular pulse line was grown before the cereal line.

That original trial was fairly small because this type of experiment is not easy to do. Now, Bett and Pozniak are taking a deeper look at this concept with a much bigger trial. 

“We have thousands of plots in our breeding programs, and nobody in their right mind is going to run all those lines one on top of the other, year after year, to identify which lines work well together in rotation. Even 100 lines of lentils and 100 lines of wheat would be an incredible amount of work,” notes Bett.

“In our project, every lentil line will get 10 different wheat lines, and every wheat line will be grown on 10 different lentil lines, meaning that the yield plots are 100 x 10. With a bit of fancy math and a lot of inference and layering understanding of the genotypes, we can make predictions as to what would have happened if we had done all 100 x 100 combinations.”

Pozniak outlines their strategy: “We will be looking for positive interactions between pairs of lines, for instance, where a particular durum line would outyield the check cultivars if a specific lentil variety was grown in the prior year. Then we want to identify DNA fingerprints that could predict the positive interactions in breeding programs. That way we could use a DNA test to select lines that would perform well in the context of a rotation.”

Bett adds, “If this approach works, then we can retreat back to our old ways of just breeding lentils and just breeding wheat and select for the regions of the genome that are enhancing the subsequent crop or taking advantage of the previous crop.”

Grain yield will be the crucial measurement in this big field experiment. In addition, the project team will be sampling the soil microbiome across the plots to see how differences in the microbial community relate to differences in crop performance in the rotation. Sean Walkowiak, a microbiologist at the Canadian Grain Commission, will be collaborating on this microbiome work.

Why lentils and durum wheat?
Bett and Pozniak chose a lentil-durum rotation for this project in part because they have the genomic resources for both crops to enable the necessary analysis – the lines in the trial are straight from the CDC breeding programs. Saskatchewan producers often grow lentils and durum in rotation to break up disease, insect pest and weed cycles, and to take advantage of nitrogen (N) fixation by lentils to reduce fertilizer needs.

If this project’s genomic breeding approach works, then researchers could investigate other crop combinations in the future. “Everybody asks us, ‘Why didn’t you put canola in the rotation too?’ It’s already a nightmare to do two crops,” laughs Bett.

She adds, “It’s very expensive to do this field experiment, but we think it is really important to look into this issue. We always recommend that you rotate your crops for many good reasons, so if we show that you are getting a yield bump, or you are saving money because you’re not having to spray as often, or you have nitrogen left over for your crop next year, that supports producer decisions to choose crop rotation. We hope this project will add even more support for crop rotation.”

Wild grass DNA to reduce N losses
This four-year project is very new, with the field experiment scheduled to start this spring, but Pozniak and Bett have already begun some indoor studies related to N cycling and N-use efficiencies. 

Pozniak is working on a novel way to develop wheat lines that reduce N losses to the atmosphere so that more N will remain in the soil for crop growth. “Nitrogen fertilizer can be converted into nitrates by the soil microbiome through a process called nitrification and this form of nitrogen can be lost to the atmosphere as a greenhouse gas. Interestingly, a few years back, scientists from Japan and Mexico identified a wild relative of wheat that sends out exudates from its roots that inhibit this biological nitrification process,” he explains.

Those researchers have transferred the DNA segment for nitrification inhibition from the wild grass into wheat. And, they have shown that, with the presence of this DNA segment, there was reduced biological nitrification.

The CDC is working with the wheat lines containing this DNA segment. “We have already sequenced the genome of a few of these lines, and through comparative analysis, we can see what DNA was transferred from the wild relative,” says Pozniak.

“We will be intensively studying that DNA segment to see what genes are there, how they work and how exactly they are interacting with other genes in the wheat genome to inhibit the loss of nitrogen from wheat production systems.”

Pozniak and his team have already initiated crosses of the material into Canadian durum wheat germplasm. “By knowing the DNA sequence and having an understanding of the genes that are there, we can perform that crossing and introgression in a much more precise and efficient way.”

He notes, “By the end of the four-year project, we’ll have breeding material in adapted Canadian wheat germplasm that is carrying this particular DNA segment and expressing the trait in a Canadian background. Of course, we’ll need to confirm the effect of that introgression on nitrification in the context of Canadian wheat production systems.”

Tracking N from lentils to wheat
Bett is collaborating on some greenhouse experiments with USask colleague Kate Congreves, who has expertise in nitrogen cycling and greenhouse gas dynamics. These experiments involve using the 15N isotope of nitrogen, or “labelled nitrogen,” which allows the researchers to track where the N fixed by the lentil plants goes and how much of this N is taken up by the following durum plants.

They aim to identify lentil lines that fix enough N to meet the lentil plant’s own needs while also leaving a good amount of N for the subsequent durum plant to use, and to identify durum lines that more efficiently use N from the lentil crop or applied N.

They also hope to gain a deeper understanding of the N dynamics in this crop rotation system, including whether the amount of N left over from the lentil crop is enough to make a practical difference in the fertilizer needs or yields of the following durum wheat.

A market for climate-smart crops?
Cropping systems with better N-use efficiency help a grower’s bottom line by reducing fertilizer needs or increasing yields. But such systems are also good for the environment because they reduce greenhouse gas emissions.

“The production of nitrogen fertilizer is a significant contributor to greenhouse gas emissions. Also, nitrous oxide, an important greenhouse gas, is lost from agricultural soils,” explains Pozniak. “We want to develop varieties that producers will incorporate into what we are calling climate-smart rotations – rotations that maximize productivity while reducing greenhouse gas emissions.”

USask economist Nicholas Tyack is working on this part of the project. For instance, he will be looking at the potential for adoption of climate-smart breeding by breeders. And he’ll assess the potential for climate-smart rotations to be profitable for producers, or whether producer adoption would need to be incentivized and how that might be done.

Tyack will also be asking consumers whether they would be willing to pay extra for climate-smart crops, just like some people pay extra for organic.

Key outcome
“By the end of the project, we’re hoping to have a better handle on how to breed for crop rotations,” concludes Bett. “Ultimately, we want to be able to deliver varieties that offer the best bang for your buck. So not only are the varieties really great in the year you grow them but they are also contributing to the next crop in the rotation.”

This project is funded by Genome Canada, Western Grains Research Foundation, Saskatchewan Pulse Growers, Saskatchewan Wheat Development Commission, Manitoba Crop Alliance, Results Driven Agriculture Research and Saskatchewan’s Agriculture Development Fund.

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