What makes a drought resistant wheat work?
By Clare Stanfield
Have you ever noticed how the leaves of a wheat plant roll up toward the middle in dry conditions? Karen Tanino will tell you that’s an avoidance strategy.
The University of Saskatchewan professor explains that leaves roll like that to reduce surface area, which reduces water transpiration through the leaf surface. And that’s not the only thing wheat plants do to fend off the pressures of drought conditions.
Tanino specializes in plant abiotic stress physiology – basically, how plants react to environmental stressors to protect themselves. She’s leading a three-year project, funded by Sask Wheat and the Saskatchewan Ministry of Agriculture through the Agriculture Development Fund, aimed at finding out what makes wheat varieties drought resistant. Her field-to-lab study is looking at 20 spring wheat and 10 durum varieties that have shown a range of drought resistances in the field across several variety trials.
“We are utilizing the wheat varieties developed by breeders at the Crop Development Centre and Agriculture and Agri-Food Canada,” says Tanino. “We bring them into the lab and ask why – what makes them more sensitive or more resistant to drought? It’s a way to capitalize on all that breeding material that has already been selected for in the field.”
But what is she looking for, exactly – genes? In a way, yes, but Tanino says this project is focused more on identifying the biochemical markers and physiological characteristics that make some varieties grow and behave in certain ways under drought stress Wheat breeders can use this information to faster select drought-adapted wheat varieties in breeding programs.
Roots and leaves
There are basically two ways a wheat plant can reduce its drought stress “A plant can take up more water or lose less, or both,” says Tanino. “The most stress-resistant plant has the most tools in its toolbox.”
There are basically two ways a wheat plant can reduce its drought stress. “A plant can take up more water or lose less, or both,” says Tanino. “The most stress-resistant plant has the most tools in its’ toolbox.”
To this end, Tanino and her team are looking at both root architecture and leaf structure (namely leaf wax, as well as the presence of specific cells and essential ions) that relate to drought-avoiding behaviours.
In the case of roots, the team is looking at plant responses to simulated drought stress, which is created by adding salinity (salt) to a growth media (agar) to impose physiological drought. Researchers then looked at root development, the rate and angle of growth under different saline concentrations, from the embryo in the seed to the 5+ tiller stage.
“One of the unique things about our study is that, for the first time anywhere, we’re developing a Zadoks scale for the roots to determine the root stages that correspond to the Zadoks scale of the shoots as a predictive model,” says Tanino. “It is important to first identify the baseline root stages in order to more accurately compare how differently a resistant plant’s root architecture reacts to drought stress compared to a sensitive plant.”
Similarly, she’s looking at leaves from a different perspective. “Most studies focus on the stomata, the pores on the leaf that open and close, and many don’t think about the cuticular wax layer,” she says. Leaf wax, of course, helps reduce water loss through transpiration and is a desirable trait for breeders.
“Our lab is focusing on avoidance strategies,” she says. “Whether that’s trying to find plants that generate more roots or have less water loss through leaves or both.”
Halfway through the project, Tanino’s team has already developed a root tolerance index for screening purposes. At the end of three years, the goal is to identify leaf traits of promise, and develop a Zadoks scale for roots, which will form the baseline to identify the mechanism of drought stress resistance. The long-term goal is to have a comprehensive field-based, high-throughput phenotyping technology in place so that wheat breeders can quickly, accurately and confidently select for drought resistance.