In an effort to enhance the resilience of apple trees amidst a warming climate, researchers in Michigan are on the lookout for a unique species known for its late blooming ability. The Malus coronaria, a native apple tree in Michigan, has adapted to combat frost by flowering two to three weeks later than cultivated apple varieties such as Honeycrisp and Red Delicious. According to Steve van Nocker, a plant geneticist and professor at Michigan State University, this seemingly small delay is often sufficient for the flowers to avoid damage from late spring frosts.
Van Nocker aims to pinpoint the genes responsible for this later blooming in the Malus coronaria to develop new apple varieties that are more resistant to frost. This ambitious project involves extensive fieldwork, including hiking through forests to locate these elusive trees and gather genetic material. His initiative reflects the broader trend among researchers and growers working to enhance apple resilience in the face of changing weather patterns linked to climate change.
In other parts of the world, such as Europe and South Korea, growers are implementing innovative techniques, including the use of solar panels in orchards and vineyards. These panels not only shield the fruit from hail and excessive sun exposure but also allow for the admission of light and heat when necessary, as explained by Jared Buono, director of Cornell University’s Hudson Valley Research Lab. His team is currently trialing solar panels in their own experimental orchard.
Additionally, researchers at the University of Maryland have successfully developed a more heat-resistant apple variety, while at Penn State University, a team has designed an unmanned vehicle powered by propane heaters that can navigate through orchards to warm the trees automatically. Buono highlighted that such strategies are essential for alleviating the adverse effects of unpredictable weather patterns, citing the significant frost event on May 18, 2023, that resulted in a 20% reduction in apple production across New York state.
The challenges farmers face have been exacerbated by climate change, leading to a more variable weather landscape. A recent study from Washington State University indicated that key apple-producing regions, specifically Washington, Michigan, and New York, have been experiencing a decrease in cold days and an increase in warm fall nights. Moreover, Washington is experiencing more frequent extreme heat events. The study analyzed climate data spanning from 1979 to 2022, concluding that these temperature trends could affect the timing of blooms, causing trees to exit dormancy prematurely and resulting in a higher risk of sunburn that can diminish the quality and appearance of apples.
On a brisk December day, Van Nocker and graduate assistant Lily “Kaz” Christian trekked to a public park near Michigan State in search of Malus coronaria trees they had previously discovered. Historically, the sweet crabapple was abundant in Michigan, even designated as the state flower in 1897. However, this species is now reportedly declining due to urban development reshaping the landscape where these trees once thrived. Van Nocker noted that many remaining trees produce limited new growth or fruit.
Upon reaching the trees, Van Nocker and Christian collected small samples of the stems for testing to ensure they were genuine Malus coronaria and not a hybrid. These samples, together with cuttings obtained from earlier expeditions, will be grafted onto apple rootstocks, allowing them to develop into trees that mirror the original specimens. However, Van Nocker emphasizes that their goal is not to replace popular varieties like Fuji or Honeycrisp, since the fruit of Malus coronaria is small, green, and bitter, an unappealing option for commercial use.
The ultimate objective is to identify the genes responsible for the late bloom characteristic and create a genetic base that breeders can utilize in developing new commercial apple varieties. In a further step to preserve the genetic material, Van Nocker is also sending seeds to the U.S. Department of Agriculture to ensure they are not lost as the Malus coronaria population diminishes.
The process of breeding a later-blooming apple variety could span several decades. If a cross is made between the Malus coronaria and a commercial apple tree, it will take approximately four to five years for the resulting tree to bear fruit. Continued breeding efforts will refine the apples to combine the best traits from both parent plants. However, Van Nocker insists that this work is essential.
He stated, “Given the changing climate, there’s a genuine risk that apple cultivation may become untenable in Michigan in the future. Therefore, improving cultivars to enhance frost resistance is absolutely vital.”
