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Accelerating drought tolerance in wheat

In Western Canada, wheat is the largest acreage cereal crop, however increasingly variable climate conditions and stresses such as drought can affect plant development, yield and profitability for growers. Researchers and plant breeders are looking for new tools and strategies to advance high yielding, more drought tolerant varieties of high quality wheat for growers.

September 25, 2018
By Donna Fleury

Scanning electron micrographs of spring wheat cultivar Stettler flag leaf epicuticular wax. The top panel depicts the adaxial leaf surface composed of wax platelets. The bottom panel depicts the abaxial leaf surface composed of rod-like beta-diketone tubules. Selection of new cultivars with preferred epicuticular wax profiles will hopefully improve whole plant water transpiration rates and overall drought tolerance. ​ In Western Canada

“Our broader research program is focused on abiotic stresses of plants and takes an approach of avoidance to stress rather than tolerance,” explains Karen Tanino, professor and research scientist at the University of Saskatchewan. “Looking at the history of the mechanisms of plants that allowed them to colonize the land, they were mainly avoidance strategies. For example, the cuticular layer of the leaves was developed to prevent moisture losses. The combined cuticular layer and cell walls provide an effective barrier to various stresses enabling avoidance strategies, whether it is to drought or frost or many biotic stresses. Crops are continually exposed to various stresses in the field and no one knows which stress will predominate in any given year. Therefore, our approach to several projects in our program is looking at a plant strategy of barriers and avoidance to multiple stresses.”

Field to lab approach
A recent project launched in 2017 is looking at the development of new screening tools to help accelerate the selection of drought resistant lines in spring wheat breeding programs. Tanino works closely with plant breeders at the University of Saskatchewan’s Crop Development Centre, along with Agriculture and Agri-Food Canada, representing the largest cluster of crop breeding programs and germplasm in Canada. “We no longer think about a lab to field approach, rather we strongly believe in a field to lab and back to field approach to accelerate improvements in plant breeding,” Tanino says. “We start in the field first working with the breeders from the very beginning and utilizing all those decades of selection material. We asked them to identify contrasting resistant and sensitive wheat lines for our project, and once we have completed our part of the research we will go back to the breeders with our physiological and biochemical markers for selection, and validate them in the field again to see if they hold up.”

The two contrasting wheat cultivars selected for the project include ‘Stettler,’ which tends to perform well in the field in drought stress years, has a lower drought susceptibility index, greater harvest index and water-use efficiency, and ‘Superb’ a cultivar which tends to perform poorly under field conditions in drought stress years. Researchers wanted to understand why the contrasting cultivars are different and identify the compounds that distinguish drought resistant types from sensitive types. A suite of methods was used to compare the composition of cuticular leaf waxes of the flag leaf of the two contrasting cultivars. The comparison is done at the molecular level to try and identify physiological and biochemical markers to complement breeding programs and their efficiency of cultivar selection. The leaf cuticle is the first line of defense for the plant, whether to abiotic stresses such as drought or frost, or biotic stresses such as diseases, insects and other pests. Although there have been several water use efficiency studies completed on crops, many of the studies have focused on water losses from the leaf stomata, overlooking or possibly underestimating the importance of the cuticle in water loss prevention and drought resistance.

“In this project we used various lab methods, including the Canadian Light Source (CLS) synchrotron, electron microscopy and wetlab techniques to profile the biochemical and physiological components of the epicuticular waxes,” Tanino explains. “One of the advantages of the CLS synchrotron and the attenuated total reflectants device, which has several different beam lines, is we can measure molecular profiles in one beam line, and then take the sample over to another beam line to measure something else. Each different beam line gives different response measurements.” A synchrotron is a source of brilliant light that scientists can use to gather information about the structural and chemical properties of materials at the whole tissue, cellular and molecular level.

Breeding with goals in mind
One of the goals of the project was to identify a specific component in the cuticle layer that is directly related to hydrophobicity, which will prevent water loss or frost, and then look at the metabolic regulation of that compound in the system. That information, together with more specific tools at the biochemical and physiological level can be provided to breeders to use in their cultivar selection process. A screening tool and protocol have been developed so far, and the next steps are to take it to the next level for more rapid, high throughput methods that breeders need. The screening protocol has been developed with spring wheat cultivars, and other crops will be added to the research in the future. The selection of new cultivars with preferred epicuticular wax profiles and cell wall profiles will hopefully improve whole plant water resistance to multiple stresses. ​

“We are also working on another project using a new seed treatment that induces earlier germination under cool temperature conditions in the majority of over 30 different crops and cultivars tested to date,” Tanino says. “The seed treatment also provides for faster root establishment and more lateral root growth. The project began in the university research field plots, but in 2018 included an 80 acre commercial farm field trial near Saskatoon. The seed treatment will be inexpensive, easy to apply and is also suitable for organic production. So far results are positive, showing enhanced root growth in the farm field, helping earlier establishment and potentially avoid heat and drought stress during flowering, and avoid fall frosts through earlier maturity. We are interested to see the yield results this fall and hope this product, which has a patent pending, will be available in the near future for growers.”

Tanino adds, “we recognize that plants face multiple stresses, so we continue to develop new tools to rapidly select and screen molecular compounds for multiple stresses. The best adapted plants have more tools in the toolbox and use multiple mechanisms to avoid stress, making it more complicated, with no one silver bullet solution. But the cuticular layer and cell wall represent a critical barrier point to avoid many stresses. By collaborating with our plant breeder colleagues to identify key traits of interest in these cuticular layer and cell wall regions that can be targeted and rapidly screened, we hope to speed up the development of drought resistant and other stress resistant cultivars for industry.”