WSU Researchers Improve Cold Hardiness Measure for Apples and Sweet Cherries
Researchers at WSU Prosser Irrigated Agriculture Research and Extension Center (IAREC) are developing a more accurate cold hardiness measurement system for apples and sweet cherries. The new three-year project, currently funded by the Washington Tree Fruit Research Commission, will help Pacific Northwest growers better protect orchards from frost damage.
Led by AgWeatherNet director Gerrit Hoogenboom and research associate Melba Salazar-Gutierrez, the project will ultimately provide more updated information about how new apple and cherry varieties handle cold at different stages of growth.
“Historical cold hardiness data are based on research that was conducted 30 to 40 years ago and with older varieties,” Salazar-Gutierrez said. “These data are still being used today, even for new varieties. So far, little is known about the hardiness of new cultivars under local weather conditions. There is a need to update this information using current varieties with new scientific methodologies.”
Frost in early spring often damages apple and sweet cherry buds and blooms, and crop resistance to freezing temperatures varies depending on the buds’ development, Salazar-Gutierrez said. This variable susceptibility to cold makes it difficult for growers to know when to take frost-protection measures.
“From dormancy to fruit set, the flower bud undergoes a number of developmental changes that are associated with a progressive, increasing vulnerability of the pistil [the female reproductive part of a flower] to low temperatures,” Salazar-Gutierrez said. “In dormant flower buds, the effect of freezing temperatures is not uniform, as ice crystals form in only some floral tissues. At full bloom, the damage may be more extensive, depending on the severity of the freeze. With cherry, flower buds are more susceptible to injury than vegetative buds.”
Previous cold hardiness measurements were also not as specific as this new system. Researchers made observations and took samples of buds and flowers after naturally occurring freeze events to determine injury, Salazar-Gutierrez said. They also tested freeze tolerance using differential thermal analysis to come up with predictions of critical lethal temperatures, but this technique is only effective for early stages of bud development.
The Vending Machine
The new system of measurement more accurately determines lethal temperatures for later bud and bloom growth, Salazar-Gutierrez said. An automated freezer sampler, called the “vending machine,” exposes the buds to different durations and controlled cold temperature combinations. Developed by John Ferguson, an IAREC staff member who also came up with a cold-hardiness prediction model for grapes, the vending machine is a standard environmental chamber with a built-in slot at the bottom of the door–hence its nickname.
Four plastic racks inside the chamber hold the samples in perforated cylinders. When the samples reach a designated temperature, they are automatically released from the racks and fall through the door’s slot into a basket outside the chamber. The customized freezer can hold a broad range of limb cuttings and flowers plus run samples overnight, processing more samples faster than previous methods.
Hoogenboom, Salazar-Gutierrez, and their AgWeatherNet research team studied Red Delicious, Gala, and Fuji apples as well as Bing, Chelan, and Sweetheart cherries beginning in February. They collected samples from the WSU Roza Research Farm and C & M Orchards near Prosser and tested them at temperatures ranging from –40 to 30 degrees Fahrenheit at varying times to learn how and when each variety’s buds and flowers were affected.
Expanding the Model
The team is still analyzing the results from this past spring. Salazar-Gutierrez said the next step is to continue collecting samples on new orchards for two more seasons, which will depend on cooperation from growers willing to participate in the project. The researchers also want to study how apple and sweet cherry buds fare as orchards enter dormancy in fall and winter. The researchers will then develop a model for growers with a range of early spring temperatures that apple and sweet cherry buds at all stages of development will tolerate.
“The overall outcome of this project will be updated hardiness charts for apples and sweet cherries that include the critical temperatures for each of the different stages of spring bud development,” Salazar-Gutierrez said. “This is a very important tool for growers who are monitoring their individual apple and cherry orchards for appropriate crop management and activation of frost protection systems. This will allow for better planning to improve fruit quality, enhance yield and ultimately increase net returns.”
Researchers Propose New Way to Save Africa’s Beleaguered Soils
A Washington State University researcher and two WSU graduates make a case in the journal Nature for a new type of agriculture that could restore the beleaguered soils of Africa and help the continent feed itself in the coming decades.
Their system, which they call “perenniation,” mixes food crops with trees and perennial plants. Thousands of farmers are already trying variations of perenniation, which reduces the need for artificial inputs while improving soil and in some cases dramatically increasing yields. One woman quadrupled her corn crop, letting her raise pigs and goats and sell surplus grain for essentials and her grandchildren’s school fees.
WSU soil scientist John Reganold wrote the article with Jerry Glover (’97 BS Soil Science, ’98 BA Philosophy, ’01 PhD Soil Science) of the USAID Bureau for Food Security and Cindy Cox (’00 MS Plant Pathology/Phytopathology) of the International Food Policy Research Institute. The article, “Plant perennials to save Africa’s soils,” appeared in the Sept. 20 issue of Nature.
The authors argue that perenniation offers a powerful option for a growing population that struggles to eat. This is especially applicable in sub-Saharan Africa, where one-fourth of the world’s undernourished population lives on nutrient-poor soils that produce one-tenth the yields of crops in the U.S. Midwest. Farmers often make these lands worse by adding conventional mineral fertilizers without organic inputs.
“Of the various factors needing urgent attention to increase agricultural productivity, scientists from the region have identified soil quality as a top priority,” the researchers write. “We believe that perenniation should be used much more widely to help farmers meet the challenge of improving soils while increasing food production.”
Several efforts to increase perenniation are already underway, including perennial grain research at WSU and millions of plantings across sub-Saharan Africa in the Trees for Food Security project. But the researchers argue for elevating perenniation research to the levels of support given mineral fertilizers and seed development.
The cost could run to tens of millions of dollars. “Yet such numbers pale in comparison to the losses of nitrogen, phosphorous and potassium from sub-Saharan farm fields each year,” the researchers explain. Such losses, they add, are the equivalent of billions of dollars of fertilizer.