Good Fruit Grower

September 2016

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36 SEPTEMBER 2016 Good Fruit Grower M att Boucher, a doctoral s t u d e n t a t C o r n e l l University, thinks insect transmission is one way fruit trees contract fire blight. So, he's working to identify which bugs are responsible and, ultimately, to develop preventive management strate- gies to disrupt the process. His work is a continuation of research started in the early 1900s, then unac- countably abandoned in the 1930s, prior to World War II. Early researchers believed insects had a passive role in fi re blight transmission. They posited a pro- cess of disease spread from infected to healthy surfaces by means of bug move- ment from one to the other. It's not a long reach, considering the ease with which bees track viral and bacterial disease into their hives. They do so by picking up infected pollen and bringing it home. However, Boucher said, some research suggests insects might play a more active role: carrying the bacteria inside their guts, incubating it for a period of time, before carrying it to and infecting new hosts, such as fruit trees. Understanding the pathogen Boucher's interest stemmed from a conversation with George Sundin, a Michigan State University plant pathol- ogist, about the possible interaction of pathogens in insect guts and hosts. The discussion centered on novel type III secretion systems (T3SS), which are hol- low needlelike structures that bacteria use to transmit disease-causing proteins into hosts. Plant pathogens can have multiple T3SSes, and they can be active at different times during the disease cycle, Boucher said. For example, one may be active during plant infection, while others are active during insect vectoring. Fire blight bacteria have three T3SSes. Sundin's group successfully knocked out the one responsible for plant infection, and no fi re blight symptoms appeared on fruit. They have hypothesized that the remaining two are active in the insect when it transmits the disease. So why not just use genetic engineer- ing to disrupt T3SS function, much like an Ohio State University horticulture research group did a few years ago? There are two reasons, said Boucher. First, the chances of the federal govern- ment allowing an altered bacteria to be released into the environment are very low. Secondly, an altered bacteria is a weakened bacteria and would not sur- vive competition in a world populated by unaltered bacteria. So Boucher is working to identify which insects are transmitting fire blight and, in addition, to determine if the T3SSes are active once the insect is infected. "Do they allow the pathogen to persist in the insect's gut for a longer time? Do they change the insects' behav- iors?" he said Which bug? Boucher will be capturing insects from yellow sticky cards in a fire blight-in- fected orchard through September for his research. Each tree has two cards, one in the canopy and the other down on the trunk at knee level. Boucher places the cards on 20 trees, collecting a total of 40 cards each week. Then he takes the cards back to the lab, removes the bugs and grinds them up. "We run DNA tests to see if they are carrying the pathogen," he said. He's also catching bees on flowers using collection vials. Can fi re blight per- sist in hives? The answer is no. "But we have no information about what's inside their guts," he said. Anecdotal suspects Early in his research, Boucher impli- cated potato leafhopper as a fi re blight vector but has not yet confirmed it. Already, he has collected 400 potato IFTA New York study tour A Cornell University doctoral student seeks to identify which insects transmit fi re blight bacteria. by Dave Weinstock Bli & bugs Matt Boucher hand collects bees from blossoms in an orchard infested with fi re blight. Boucher is capturing bees and other insects in an effort to "When �lies land on the margins of the canker's ooze, they could be picking up bacteria for possible transmission." —Matt Boucher ght

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