Issue link: http://read.dmtmag.com/i/84143
fireblight pathogen Erwinia amylovora. Pusey doubts that further bacterial strains will be discovered that are more effective and says research is needed on ways to make Bloomtime more effective. An important step forward was a model he developed using crab apple that led to a better understanding of how the disease becomes established in flowers. He looked at how water, temperature, and flower age affected microor- ganisms and disease development. For his work, Pusey used potted crab apples in the greenhouse, which can be manipulated to bloom year round. "That's been a handy tool that we can use throughout the year to learn more about this disease and how to control it," he said, noting that other scientists have used the model also. When Pusey began working on fireblight, little was known about the ecology of the flower parts, and particu- larly the stigma, where the fireblight pathogen initially builds up. He has devoted much time to sampling flowers and looking at the interaction between microorganisms on the surfaces of the flower parts. What Pusey found was that conditions on the stigma are conducive to a large diversity of bacteria, including the pathogen and beneficial microorganisms. Later, when there is moisture from rain or dew, the pathogen moves down into the flower's hypanthium, a high-sugar environ- ment that is more hospitable to yeasts. A yeast-based prod- uct called BlossomProtect, containing Aureobasidium pullans, is available as a fireblight biocontrol and could act as a second line of defense against the pathogen, Pusey believes. He has been pursuing the idea of combining Bloomtime with BlossomProtect or other yeast biocontrol and is looking at whether they would be compatible. Other strategies Pusey has also been collaborating with scientists around the world on other strategies that might help growers better fight the disease in the future. For example, nanoengineers at the University of Illinois are working on controlled-release microcapsules that might lead to bet- ter dispersal and survival of the organism in the orchard. Scientists with Agriculture and Agri-Food Canada in Vineland, Ontario, are exploring the use of bacterio - phages (viruses that reproduce within bacteria) that could attack the fireblight organism, with Bloomtime used as a carrier. Ultimately, Pusey believes fireblight-resistant varieties will be the answer. Cornell University in New York has developed resistant apple rootstocks, an important step in preventing infected trees from being killed. "A lot of the dwarfing rootstocks that are commonly used aren't very resistant to fireblight, and I've looked at samples that have come to me from growers—cases in which the organism moved from the blossom right down to the root and killed the whole tree in a relatively short time," he said. "This happens with young trees especially. A lot of times, you may not see the symptoms on the scion before the tree collapses." Developing a tree that would resist infection would be difficult using traditional breeding techniques, since the variety would also need all the desirable tree and fruit characteristics to make it a commercial success. However, Pusey has been working with Dr. Bruce Barritt, retired apple breeder at Washington State University, and his successor Dr. Kate Evans to develop methods to screen seedlings for fireblight resistance. "I think, ultimately, resistance would be the answer, but that takes a long time," he said. Dr. Jim Mattheis, research leader at the Wenatchee lab, said Pusey's research advanced the knowledge of fireblight and demonstrated the potential for biological disease management, and he leaves ARS as a member of active collaborative projects that will continue the investigations that he initiated. His position will be filled, though it is not known when, Mattheis said. www.goodfruit.com • GOOD FRUIT GROWER OCTOBER 2012 7 800.743.2125 | farm-credit.com Operating & Real Estate Loans Crop Insurance Country Home Loans Appraisals