By Kavi Raj Acharya and Shui-zhang Fei, Iowa State University
When temperatures plummet, perennial ryegrass, an important cool-season turfgrass, often struggles, leading to winterkill and patchy turf in spring. It’s well documented that cold acclimation, an exposure to low temperatures and short daylength, leads to significantly enhanced cold hardiness in plants adapted to the temperate regions. However, most studies only focus on the effect of cold acclimation at non-freezing low temperatures. Given the frequent occurrence of subfreezing events in northern climates, it’s important to understand how plants respond to subfreezing temperatures.
We simulated a sub-zero acclimation (SA) experiment in which we deliberately exposed perennial ryegrass plants to freezing (-2°C) but non-lethal temperatures for specific periods. This controlled stress triggered natural defenses within the plant, allowing it to better withstand even harsher conditions later. Perennial ryegrass plants given this extra cold exposure developed a much greater ability to survive severe freezing. We measured this ability by measuring LT50, the temperature at which half of the tested plants die due to injuries caused by freezing stress. Our observations revealed that plants exposed to sub-zero temperatures have lower LT50 values (a difference of more than 2°C) than the plants cold acclimated at non-freezing low temperatures (Fig. 1).
What’s more exciting is that this gain in freezing tolerance followed a clear trend based on how long the plants stayed in sub-zero conditions. One week of subzero acclimation gave some benefits, but two weeks led to a much stronger response. We collected leaf tissue from each treatment to perform molecular tests that paint a picture of what is happening inside ryegrass cells, leading to enhanced cold hardiness. This approach will let us see which genes are switched on or off and how accessible those genes are under such stressful conditions. By identifying these molecular changes, we hope to uncover the genetic and epigenetic switches that drive cold resilience in perennial ryegrass.
These insights have real-world significance. If turf managers, breeders, and researchers can select for varieties that naturally respond well to sub-zero cues, we might develop more winter-resilient grass varieties. That could mean fewer dead patches in spring, less reseeding, and more consistent turf quality for golf courses, sports fields, and lawns.