Cherry trees keep their buds super-cool in winter

Researchers at UBC Okanagan are working to learn more about how sweet cherry trees naturally protect their buds from freezing during cold winter months.

Dr. Elizabeth Houghton recently graduated from the Irving K. Barber Faculty of Science’s Department of Biology. Her latest paper, published in Plant Biology, examines how sweet cherries, like many fruit trees, use a natural survival strategy called supercooling to protect undeveloped flower buds during freezing temperatures.

This is critical for fruit trees because these flower buds must survive the winter to produce the following year’s crop.

In late January 2024, temperatures in the Okanagan dipped to –27°C, causing severe damage to many fruit trees. Estimates indicate that 90 per cent of the anticipated summer crop was destroyed.

While many trees have natural methods to survive harsh winters, a supercooling survival process in stone fruits still raises questions for researchers.

“Plants like sweet cherries can survive freezing temperatures in winter using supercooling. When in a supercooled state, the liquid in plant cells can avoid freezing, even at temperatures well below 0°C —we call this a metastable liquid. However, the liquid can freeze if triggered by an impurity or ice particle,” she says.

“We don’t fully understand how this works in some plant structures, and we wanted to learn more about how sweet cherry flower buds survive cold temperatures.”

While most research on stone fruit-bearing trees has focused on peaches, Dr. Houghton notes that little attention has been paid to sweet cherry flower buds containing multiple primordia. These cell structures develop into a flower and eventually produce fruit, rather than just a single one like those of a peach tree.

Dr. Houghton examined several factors to better understand supercooling, including how ice forms in the buds, how the outer layers freeze, and the internal changes buds undergo as the weather warms and spring approaches.

Dr. Houghton notes that cherry trees are especially vulnerable in early spring because they lose their ability to supercool as the buds grow. A sudden cold snap can be disastrous, she explains.

“Cherry buds have a special way of protecting themselves from freezing in winter, but as buds grow in the spring, they lose some of that protection,” says Dr. Houghton.

“We are trying to understand better how these fruit buds survive extreme winter temperatures,” she adds. “And because there is some debate about what winters might look like in the future—we may experience more extreme cold snaps—it’s important that we learn from the cherry trees to work towards protecting fruit crops.”

The governments of Canada and British Columbia funded this project through the Canadian Agricultural Partnership, a federal-provincial-territorial initiative. The Investment Agriculture Foundation of BC delivered the program.

An anonymous private foundation, Agriculture and Agri-Food Canada, the BC Cherry Association and the Natural Sciences and Engineering Research Council of Canada provided additional funding.