Roots of resilience: the experts working to bolster apples against the climate crisis | US news

Terence Robinson still remembers the Valentine’s Day Massacre – from 2015, not 1929.

For the professor of horticulture at Cornell University, the term does not evoke Tommy Guns and Al Capone’s Chicago. Instead of a gangster, the culprit in Robinson’s massacre was the weather. And its victims were the apple orchards of the northeastern United States.

“We had a warm-up in February, and then a big cold air mass moved toward New York and spread up to the Pennsylvania fruit zone,” he recalls. “In the spring, we started to see damage to the trees. »

Some scientists have called this phenomenon the “rapid decline of apples.” Robinson and his colleagues concluded that the sudden drop in temperature, down to 36°C within a few days, had shocked the orchards, which had begun to emerge from dormancy due to the earlier heat. They also found that the most critical damage was not to the trunks or branches, but rather to the rootstocks, the very foundations of the trees.

These foundations are often quite old. The widely planted M9 rootstock, for example, was developed at the East Malling Research Station in England more than a century ago. But as extreme weather brought on by the climate crisis continues to accelerate, scientists like Robinson are growing increasingly concerned that tried-and-true rootstocks won’t stand up to the tests of decades to come.

Damage to rootstocks means damage to the U.S. apple industry, which generates about $23 billion in annual economic activity and produces more than 11 billion pounds of the nation’s most consumed fruit. That’s because almost all commercial apple trees are actually a combination of two separate plants.

The apple-producing part of the tree, called the scion, starts with a cutting of a variety like Gala or Red Delicious. Nurseries then remove all but a small portion of a different tree, the rootstock, and graft the scion onto that base. The technique combines high-quality fruits with roots that govern commercially important characteristics like dwarfing stature (critical for efficient harvesting).

Robinson, along with U.S. Department of Agriculture (USDA) scientist Gennaro Fazio, co-leads the only effort in North America to give commercial growers a new foundation for their orchards. Together, Cornell University and the USDA conduct the Geneva apple rootstock breeding program at a research station in Geneva, New York.

Since 1968, researchers like Robinson and Fazio have been crossing and evaluating apple trees, searching for rootstocks more resilient to a changing world. While the program initially focused on disease resistance, particularly to a bacterial infection known as fire blight, breeders began to place more emphasis on the traits that apple rootstocks will need to succeed in the future.

“We continue to want to have a dwarf rootstock, because dwarf orchards are much more profitable and produce early,” Robinson said. “We have expanded our list of goals for this program to include drought resistance, tolerance to high-salt soils, and the ability to withstand more moderate winters. »

This is a project that rewards patience. Crossing trees from different rootstocks, selecting their offspring for desired traits, and ensuring that the new rootstocks perform in real-world settings can take 30 years or more. Cornell didn’t release its first commercial variety until 1997; the first crosses of three varieties launched in 2023 were made in the 1970s.

Robinson himself has worked on the program since 1991. “It takes a long-term commitment to learn to love apple rootstocks,” he said.

The key to success over these long durations, suggests Lee Kalcsits, may involve selection without regard to a specific climate. A professor of fruit tree physiology at Washington State University, he leads the Building Climate Resilience of Pears and Apples (Sparc), a national research effort dedicated to protecting fruit trees from extreme weather events. (Fazio and Robinson are also members.)

When growers start a new apple orchard, Kalcsits explains, they are making an investment that they believe will pay off over 15 to 30 years. Even though they may be confident in the broad outline of their region’s climate over time, unexpected events that occur in the years after planting can devastate their long-term yields.

Research published by Kalcsits and colleagues in 2024 found that in apple-growing regions across the country, fall and spring temperatures are warming. This makes it more difficult for some apples to meet their chilling requirements, a minimum period of cold that a tree must experience before flowering. Trees also respond by entering dormancy later and exiting earlier, creating a longer window of vulnerability to any cold spells that occur.

And as the climate crisis weakens the polar jet stream, allowing cold air from the Arctic “polar vortex” to reach more of the United States, drastic swings in winter temperatures are becoming more common. Robinson notes that devastating cold snaps have since hit some of the major apple-producing regions of the United States, including southern Pennsylvania and western Michigan, four times since 2015.

Rootstocks determine how trees respond to climate. Through their interactions with the scion, rootstocks can cause apple trees to remain cold-acclimated longer or require less chilling to open their buds. Rootstocks can even help apples survive on less water by reducing scion activity during drought. All of these traits improve general resilience, rather than being optimized for certain conditions.

“We need to be aware that the rootstocks we select are adaptable. It’s not that they are suitable for a future climate, but that they are adaptable,” Kalcsists said.

The Cornell/USDA breeding program is already helping rootstocks resist false springs followed by cold snaps, with the new varieties showing much less damage than the standard M9. By continuing to crossbreed these new rootstocks, scientists hope to combine forces and produce superior options for dealing with climate change. They are also looking to wild apples harvested in Central Asia, where apples were first domesticated, to create new reservoirs of genetic diversity.

Once these crosses are made, the most promising offspring are tested across the country in a collaboration called NC-140. One of these experimental orchards is at North Carolina State University’s Mountain Horticultural Crops Research Station, about 20 miles south of Asheville.

On a sunny late winter day, Fruit Tree Extension Specialist Mike Parker walks among the neat rows of his rootstock trials. The skinny, leafless apple trees rest on a five-wire trellis anchored by thick wooden posts, a support system to help their small trunks support their fall harvest.

Most of Parker’s trees will grow here for a decade, with scientists collecting details each year on survival rate, trunk size, fruit size and yield. This long-term data helps breeders and horticulturists have confidence that new rootstocks will perform as they originally envisioned – or rule out candidates that present unexpected problems.

“When we do repeated trials in multiple states, there are things we find out very quickly, like this rootstock is a dog and is not going to fly,” Parker said with a smile. “We would much rather kill trees at our research station than have growers lose trees on their farm. »

Like Robinson, Parker is a veteran of this work, having taken over rootstock evaluations from North Carolina State University in 1996. And like his Cornell colleague, he plans to retire in about a year.

Robinson worries about how rootstock development will change as his generation of scientists ages and moves away from orchard research. Although research funding has so far remained relatively constant and his work has enthusiastic support from trade groups such as the US Apple Association, he says younger scientists are more interested in selecting scions than in patiently waiting to develop rootstocks.

Long-term perspectives in general, he continues, generally seem less popular with funding agencies in the current scientific climate.

“I’m afraid they’re going to say, ‘We have enough rootstock, let’s end this initiative.’ And for the problems we’re facing right now, we probably have a good set of rootstocks. But it’s these emerging issues, that you haven’t really thought about or planned for, that you might not be able to address if they shut down the program.