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Tuesday, September 28, 2021

UC Davis prepares new walnut variant for the market

The novel nut variant, UC Wolfskill, can be harvested earlier than current varieties, increasing harvest efficiency

UC Davis is getting ready to release their new walnut variant, UC Wolfskill, to farmers all over California after an 18-year process. Researchers created the UC Wolfskill walnut after initially crossing the Chandler and Solano walnut in 2003, according to Pat Brown, breeder and an associate professor in the department of plant sciences. The variant is named after one of the first American settlers in northern California that donated the Wolfskill ranch to UC Davis for tree research.

Brown’s responsibility, along with coordinating the entire process, is to make new crosses annually by planting seedlings and deciding which seedlings are to become selections for cross breeding. The best selections will be used in grower trials by farmers willing to dedicate a plot of their land to observe and report the progress of the new variant.

         According to Brown, the most popular variety in California and the rest of the globe is the Chandler walnut, due to its ease of planting and because farming produces high-quality crops. The downside with Chandler walnut is that it harvests late, resulting in the investment of harvesting equipment, hauling equipment and drying equipment across California simultaneously for a narrow window of time. Brown noted this problem was the motivation for creating the UC Wolfskill walnut.

         “Our goal in developing this variety is to have something that’s earlier, to spread the harvest window [and] to increase the efficiency of those big capital investments, but to maintain the Chandler quality,” Brown said.

         The Chandler’s light golden color is also a reason it is in high demand, according to Brown. Chuck Leslie, a breeder with the UC Davis Walnut Improvement Program and specialist in the plant sciences department, knows that walnuts are desired based on their ability to crack in half. Growers receive more money for walnuts in halves than in pieces. The kernel weight, or measure of seed size, is also a factor, with buyers wanting 55-57% kernel weight per nut.

         The Wolfskill cross occurred when Gale McGranahan, the past leader of the Walnut Improvement Program, and Leslie decided that instead of taking pollen from one tree and putting it on another tree, they would take pollen from a variety of trees—including Solano—and put it on the Chandler trees in what is known as a poly-cross. Chandler and Solano crosses produced the most successful trees with the desired characteristics of earlier harvest and light color, according to Brown.

         Although there were no genetic modifications done in the program, researchers used the genes of walnuts to make predictions about the walnut tree characteristics, according to Leslie. An example of what genetic markers can predict is when a tree will open its buds in the spring. The earlier the buds open in the spring, the earlier the flowers will bloom and the earlier the harvest will be. The genetic markers for different traits are developed from a full-sequence reference genome for walnuts created a couple years ago at UC Davis.

         Walnut blight, a pathogen that spreads through orchards during the spring rains, is also a concern for both Brown and Leslie because it is hard to predict how the disease will affect UC Wolfskill once it is released to more farmers. The Chandler’s late harvest, however, causes its buds to open after the spring rains, reducing its susceptibility to the pathogen.

         Although UC Wolfskill is not proven to be blight resistant, there is evidence from the grower trials that the harvest is still producing a significant quantity of nuts. It has been hypothesized that due to the high yield of walnuts, the harvest can afford to lose a small amount to blight, but according to Brown, it is still unknown. The Walnut Improvement program is currently studying this phenomenon.

         Another problem the Walnut Improvement Board is investigating is the chill tolerance of walnut trees. Climate change is causing a continuous increase in Earth’s surface temperatures and the time period for the cool winter period is decreasing, according to Leslie. The orchards of walnut trees are expected to be in the ground for 40-60 years and will encounter the effects of global warming. The program will be studying the correlation of early leafing with low chill tolerance this winter.

         The overall goal of UC Davis’ Walnut Improvement Program is to enhance the value of the walnut for the grower. It is funded by the California Walnut Board and the data is gathered by farmers who are observing the test variant on specific plots on their land.

         “If things look promising, at that stage, then we will send or try to encourage commercial nurseries around the state to get graftwood,” Leslie said.

         The nurseries, the majority located in the Central Valley of California, will have to apply to the university for a license to produce the trees. Denise Meade, the contact for nurseries that want to obtain a license, explained that any inventions developed on the UC Davis campus are required to be reported to InnovationAccess, the technology transfer office that takes care of this licensing process. The office will then examine it to determine if the invention can be protected by a patent. In the case of seed crops, a Plant Variety Protection (PVP) certificate would need to be issued through the USDA office instead of the patent office.

         In order to obtain a license, the nursery must be in the state of California unless they are joint with the USDA, and it must be already licensed with the California Department of Food and Agriculture (CDFA) to maintain the purity of the variety. Once the license is obtained, the nurseries have the right to sell trees anywhere in the U.S.

         Those who are first-in-line for the release of UC Wolfskill are farmers that already have it from the grower trials, according to Brown. There are plans for a batch of growers to get their UC Wolfskill trees this Spring, and Brown hopes that in four to five years consumers will start purchasing the walnuts.Written by: Francheska Torres —science@theaggie.org

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