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POSTERS: New and emerging diseases

Genetic analyses of the laurel wilt pathogen, Raffaelea lauricola, in Asia provide clues to the source of the clone causing the current USA epidemic
Tyler Dreaden - USDA Forest Service. Adam Black- Peckerwood Garden Conservation Foundation, Randy Ploetz- University of Florida - Tropical Research and Education Center, Marc Hughes- University of Hawaii at Manoa, Jason Smith- University of Florida

Laurel wilt is caused by the fungus Raffaelea lauricola T.C. Harr., Fraedrich and Aghayeva, a nutritional symbiont of its vector, the redbay ambrosia beetle, Xyleborus glabratus Eichhoff. Both are native to Asia but were found in Georgia in the early 2000s and since spread to much of the southeastern United States killing >300 million trees in the Lauraceae plant family. Our goals were to elucidate the genetic structure of populations of R. lauricola, examine its reproductive strategy, and investigate the number of times the pathogen was introduced to the USA. A panel of 12 simple sequence repeat (SSR) markers identified 15 multilocus genotypes (MLGs) among 59 isolates from the USA (34 isolates), Myanmar (18), Taiwan (6) and Japan (1). Limited diversity in the USA isolates and the presence of one MAT idiotype (mating type locus) indicated that R. lauricola was probably introduced into the USA a single time. Only three closely related MLGs were detected in the USA, the most prevalent of which (30 of 34 isolates) was also found in Taiwan. MLG diversity was far greater in Asia than the USA with isolates from Myanmar being distinct from those from Japan, Taiwan and the USA. Although both MAT idiotypes were present in Myanmar and Taiwan, only the population from Taiwan had the genetic structure of a sexually reproducing population. The present results suggest that a Taiwanese origin is possible for the population of R. lauricola in the USA, although more work is needed.