Good Fruit Grower

May 15

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Cherries Cherry coating SHOWS POTENTIAL C Using the right surfactant with anticracking biofilm is key. by Melissa Hansen live Kaiser knew what he wanted when he began working to develop a new anticracking protectant for cherries—a coating that would be water repellent, elastic, long-lasting, organic, and safe for humans. Developing and patenting a new anticracking material for cherries might seem beyond the duties of an Oregon State University extension "You need a robust enough surfactant that will spread on the fruit without dissolving the cuticle." horticulturist based in Milton-Freewater. But Kaiser, with previous postharvest physiology work at the University of Pretoria in South Africa that involved a sorghum-based coating for pears to extend shelf life, has long had in interest in biofilms for fruit. And, his extension work with tree fruit growers gave him firsthand knowledge of the limited tools that orchardists have to protect their cherries from cracking caused by rain. Biofilms are coatings that adhere to a surface —Clive Kaiser based on the physical properties of being are either hydrophilic or hydrophobic—water lov- ing or water repelling, he explained during a phone interview with Good Fruit Grower. The pear coating Kaiser had been involved with was hydrophilic, meaning it attracted and bonded with water. However, Kaiser thought a hydro - phobic biofilm would work better for cherries because he wanted to "keep water out, not suck it in." He teamed with OSU's pharmacology school after learning the college had patented a slow release, hydrophobic biocoating for the drug Ritalin. "That was the starting place," Kaiser said. A big plus was that the Ritalin biofilm was already approved for human consumption. He partnered with OSU's Dr. J. Mark Christensen, and they spent several years developing a novel, elastic biofilm that's tentatively been called SureSeal. The biofilm, a copolymer blend of phospho- lipids, complex carbohydrates, and calcium, has been patented. OSU is now working to commercialize the product through a private company. Kaiser placed great emphasis on finding a material that was elastic and could grow with the fruit, which would help reduce the number of applications needed. "One of the problems with waxes like carnauba that are contained in other anti- cracking materials is that they don't stretch and require numerous applications," he said. To see if the biofilm was elastic enough, it was painted on a balloon that was repeatedly inflated and deflated. No cracking or flaking was observed. Field trials have confirmed that only two applications of SureSeal are needed to provide cracking protection—one at straw color and one again ten days later. Coverage is key Several years of testing in cherry orchards in Washington, Oregon, Idaho, Chile, Tasmania, and Norway have focused on refining the rate and timing, and finding the right surfactant that must be used with it. An issue that surfaced last year dur- ing Kaiser's trials and those conducted by the Washington Tree Fruit Research Com- mission (see related story on page 26) was the importance of coverage and using the right surfactant. "The type of surfactant used is critical," he said. "You need a robust enough surfactant that will spread the product on the fruit without dissolving the cuticle in the process." Getting thorough coverage of the material on the fruit in 2011 was difficult with several different spreader-stickers used. None were as effective as a product origi- nally used in 2010, Kaiser said, explaining that different formulations were tried because of concern that the original spreader-sticker wouldn't be available in the future. However, the original spreader-sticker, an organosilicate surfactant, is now available locally in the Pacific Northwest. Kaiser's current recommendation to ensure adequate coverage of SureSeal is to mix the material in 200 gallons of water per acre and apply it with a tractor speed going no faster than two miles per hour. 24 MAY 15, 2012 GOOD FRUIT GROWER Marlene Long, left, and husband Lynn Long, far right, help Clive Kaiser collect cherry cracking data inside a cherry orchard tunnel at the Norwegian Institute for Agriculture and Environmental Research. He plans to test the organosilicate surfactant with SureSeal again this season to make sure all coverage issues have been addressed. A drawback of the organosili- cate surfactant, he notes, is that it will most likely preclude SureSeal from receiving approval from the National Organic Standards Board. Cracking reduced Since 2008, SureSeal has been tested under field conditions with different culti- vars and locations. One of the difficulties of testing anticracking materials is the uncertainty of rain. This is why Kaiser has taken his trials beyond the Northwest to Norway, where rain and hail are so common that cherries are routinely grown under tunnels. SureSeal has shown potential to reduce fruit cracking. In one trial in Norway, the control had 24.6 percent cracked fruit compared with 9.8 percent cracking in the SureSeal treatment. In some trials, when overall cracking was relatively low, SureSeal reduced cracking by 50 percent; in other trials, with higher overall cracking, the reduction was greater. But while the biofilm can help reduce cracking, even SureSeal has limits. He found in one orchard trial last year that the material was overwhelmed when 1.5 inches of rain fell during a 24-hour period. Kaiser believes there is a strong relationship between the soil water status and internal water in the fruit, and when excess water fills the soil profile, cracking can- not be avoided. In a trial in Norway, where covers protected the fruit surface from rain, cracking could not be avoided following 56 days of rain. Cracking was observed on 44 percent of the fruit inside the tunnel. The tunnels didn't have gut- ters on the sides to move excess water away from the covers, and the soil became saturated after repeated rain events. "The biofilm has potential to reduce fruit cracking as long as cracking doesn't exceed 30 percent of the fruit overall," he said. "As soon as you reach 30 percent, then soil water relations come into play and how you manage your soil moisture is critical." He believes that SureSeal will work best when used in conjunction with soil covers that help to manage soil water content. Kaiser also observed trends of increased fruit firmness, stem pull force, and sol- uble solids, and larger fruit in the biofilm treatments compared with the control. More studies are planned to further investigate his observations. In his randomized block design trials, fruit from the study trees were harvested according to industry standards, with an additional sample of 50 fruit harvested from each tree. Half of the 50 fruit were analyzed for row size, fruit firmness, stem pull force, and total soluble solids; the other half were held in cold storage for two weeks and then analyzed in the same manner as on the day of harvest. He believes he is seeing differences in fruit size because the SureSeal is acceler- ating maturity. Kaiser said he doesn't strip-pick fruit when collecting cracking data but selectively picks mature fruit from the treatment and control trees. When strip picking is used, immature fruit, which are less susceptible to cracking, are also included in the sample and would skew the results. • Photo by MELAND MEKJELL

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