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Upping durum’s dry down game

A short dry down period is a valuable advantage for timely harvesting, reducing the risk of weather damage to the grain, and decreasing the need for practices like applying a pre-harvest desiccant or using a grain dryer. Now Jatinder Sangha is leading a research project aimed at helping durum wheat breeders develop varieties with faster dry down potential.

Dry down occurs as the crop transitions from physiological maturity to harvest maturity. “Upon reaching physiological maturity, the dry matter, such as starch, nutrients and proteins, stops filling the grain, and the maximum yield potential is attained. After this stage, the grain begins losing moisture, going from around 37 per cent moisture at physiological maturity to less than 18 per cent at harvest maturity,” explains Sangha, a research scientist who is part of the wheat breeding team at the Swift Current Research and Development Centre of Agriculture and Agri-Food Canada (AAFC) in Saskatchewan.

His project was triggered by several factors. “Canada is a major durum-producing country and renowned in international markets. We are concerned about issues related to durum quality that might affect Canada’s market share, which could impact farm income and [the whole durum value chain]. One of those issues is that some European countries have voiced their concern over unwanted residues in grain resulting from the use of desiccants to facilitate early harvest. Having varieties with a short dry down potential would reduce or eliminate the need for such chemicals,” he notes.

The other trigger was that fast dry down varieties are already available for other crops such as corn. During the 2018 Durum Summit in Swift Current, a representative of Barilla, an international food company that produces durum products such as pasta, asked if durum varieties with faster dry down could also be developed. 

“That question sparked discussions with Barilla and among the scientists at our centre about whether we have right now or could we develop durum wheat with short dry down potential,” Sangha says.

The first step for Sangha’s research group was to assess the duration of the dry down period in 235 durum lines from around the world. These lines are in the germplasm collection of Yuefeng Ruan, the durum breeder at AAFC-Swift Current, and they carry unique agronomic, genetic, physiological and disease-response characteristics.

Genetics and environment each play a role in the rate of grain dry down, so Sangha’s group evaluated the 235 lines under two environmental conditions – rain-fed and irrigated – at Swift Current in 2018 and 2019. They visually monitored grain development in each line to track the changing kernel moisture content from just after fertilization to harvest maturity. They also measured the moisture content of samples using an oven-drying method. 

Out of the 235 lines, they shortlisted 110 lines that have potentially shorter dry down periods, ranging from 2.5 to 11 days, as well as other useful traits.

The project’s field work was postponed in 2020 due to COVID restrictions, but Sangha’s group is back in the field this summer. “We will be further characterizing those 110 lines at Swift Current under irrigated and rain-fed conditions and at Indian Head under rain-fed conditions,” he says. 

“Out of those 110 lines, we will be selecting the 10 to 20 best contrasting lines with very clear dry down characteristics. And then we will put more effort into fully characterizing those lines.” 

The results from that work will allow Sangha to identify which particular durum lines would be most suitable for breeders to use in developing elite durum varieties with shorter dry down potential.

Seeking quicker screening options
This characterization work involves tracking the grain filling and moisture dynamics in the developing kernels as the spike transitions from flowering through physiological maturity to harvest maturity. As part of this work, Sangha and his group are also looking for faster options to track these characteristics because these types of measurements can be time consuming and labour intensive.

For instance, the oven-drying method is a common way to measure grain moisture content. It involves weighing a grain sample fresh from the field, oven-drying it, reweighing it, and then calculating how much moisture was lost. That is no problem if you have just a few samples. But Sangha explains that the rate of dry down is very dynamic and varies with changing weather conditions, so kernel moisture content needs to be measured frequently. Imagine the labour and lab space required to use that method for all the samples that would need to be collected from fertilization to harvest maturity in a breeding program where thousands of lines have to be evaluated.  

Sangha’s group is comparing the oven-drying method with several other options. One of those options is a modified moisture meter. The commercial meters that are able to measure moisture in a single, developing seed are designed for crop types with large seeds, not for durum seeds. So Sangha’s group had to improvise – they modified a commercial meter to create a single-kernel moisture meter that works for developing durum seeds. 

Some of the other methods they are comparing include: visually rating each line for kernel moisture; using the thumb-and-finger-pressing method to determine the moisture content of individual kernels; and a vegetation index called NDVI (normalized difference vegetation index). NDVI is a way to estimate leaf chlorophyll content, photosynthesis activity and yield potential, and it is determined using sensors to measure certain wavelengths of light reflected from the plant. 

Then the researchers will relate these different measurements to the dry down potential and figure out which option is the best choice for screening breeding lines for this trait.

The grain fill and moisture data collected in this work will help increase understanding of physiological processes occurring as the kernel moves toward harvest maturity. Sangha notes, “By identifying the physiological mechanisms that influence the rate of dry down in these durum lines, we’ll have a head start on knowing how those lines might react to different environmental conditions and understanding the genetic control of the trait.”

The main funders of this project are Saskatchewan’s Agriculture Development Fund, the Saskatchewan Wheat Development Commission and the Alberta Wheat Commission. 

Looking ahead
The results from this research have the potential to benefit durum breeders, growers, exporters and processors. For breeders, the project is expected to identify durum lines with short dry down potential that could be used in their breeding programs, and to identify quicker ways to screen breeding lines for this trait. 

For growers, durum varieties with fast dry down potential would increase the chances of timely harvesting and reduce the need for swathing or applying a desiccant or the need to use a grain dryer. And decreasing the need for these practices would lower growers’ input costs, reduce their energy consumption, decrease their environmental footprint, and help maintain or increase market access for Canadian durum. 

For grain exporters, processors and consumers, Canada would continue to provide high-quality durum that meets the requirements of international markets. 

Sangha points out that the project’s results could also contribute to further improvements in durum. For instance, the results could help Sangha and his AAFC colleagues in identifying the genes affecting the rate of dry down in durum and in developing molecular markers for those genes. Then breeders could use those markers to select germplasm with shorter dry down potential in the lab without field trials.

He also notes, “This project involves a lot of fundamental physiological research. These types of fundamentals will become more and more important for understanding crop responses to environmental stresses that arise because of climate change and for finding ways to improve yield and quality under such emerging situations.”