Issue link: https://read.dmtmag.com/i/751050
www.goodfruit.com GOOD FRUIT GROWER DECEMBER 2016 73 resistant to fire blight. "It would be great if we could identify some germplasm with some level of resistance that we could then use in the breeding program." The other potential gain: Because researchers already have genotypic information for these trees, they may be able to identify some linked markers in their DNA asso- ciated with fire blight resistance, which would enable them to use DNA screening to predict which trees in the breeding program will be resistant to fire blight. Taken together, newly identified resistance genes and development of DNA markers enable researchers to pyramid multiple resistance genes, thereby improving the durability of the resistance and the efficiency of the breeding program. The research Evans and her team couldn't really inoculate her orig- inal research orchard, because the risk was too high that it would destroy the trees. Instead, she had to establish a new planting to conduct the experiments. "For a lot of diseases, like apple scab, the disease is usually widespread and uniform. It won't kill the tree. With fire blight, it's a much more sporadic disease and unless you do actually challenge the tree with the patho- gen, you don't get reliable data on susceptibility," said Jay Norelli, a plant pathologist at the U.S. Department of Agriculture's research station in Kearneysville, West Virginia. Norelli, who is leading the disease research for the RosBREED project and collaborating with Evans on this trial, has been working to characterize the underlying basis of disease resistance in fruit trees and to develop novel control strategies for specific diseases, including fire blight. Thus, the scissors to the trees. So far the trees have shown a range of responses in the first year of study. "We had great infection," she said with a laugh. "By seeing symptoms, you know there wasn't a problem with your inoculation, but we certainly saw some individuals that weren't showing any symptoms either." The results have provided a great data set for the first year, Evans said, and she intends to continue the work next year. "You can't do this kind of study on just one year's data; it's not informative enough," she said. "There will be some trees that won't make it to next year, but for those that weren't showing any symptoms, we really need to repeat the process so that we're confident with the data set that we're going to use going forward." • Targeting for tolerance J ay Norelli, a plant pathologist at the U.S. Department of Agriculture who is leading the disease research for the RosBREED project, has been working to characterize the underlying basis of disease resistance in fruit trees and to develop novel control strategies for specific diseases, including fire blight. Specifically, he and others are targeting specific cultivars that they know are fire blight tolerant and have good fruit quality, including Splendor, a New Zealand cultivar that isn't grown in the United States and never really made it onto the commer- cial market due to storage issues. "It has excellent flavor though and has been used in many breeding programs," he said. Outside of the RosBREED project, Norelli and Kate Evans of Washington State University also have identified some individuals of the wild pro- genitor of apple, Malus sieversii, that are highly resistant to fire blight. "We are trying to do that directed genetic analysis by making crosses," he said, which would introduce into the breeding program a much higher level of resistance, but because it involves breeding new varieties, rather than identifying resistance in existing varieties, "that approach will take a lot longer." "Even when starting out with good cultivars, like Splendor, the development of a new cultivar for fruit trees still takes a long time, and it takes a long time for it to be accepted by the industry," he said. "It's a major undertaking." —S. Dininny