@ARTICLE{TreeBASE2Ref26923, author = {Courtney A Gallup and Kestrel L McCorkle and Kelly L. Ivors and Howard D Shew}, title = {Characterization of the black shank pathogen, Phytophthora nicotianae, across North Carolina tobacco production areas}, year = {2017}, keywords = {Phytophthora nicotianae, Phytophthora parasitica, genetic characterization, tobacco, black shank disease, mating type, fungicide sensitivity, race, pathogen}, doi = {}, url = {http://}, pmid = {}, journal = {Plant Disease (APS Journal)}, volume = {}, number = {}, pages = {}, abstract = {Black shank disease of tobacco, caused by the oomycete Phytophthora nicotianae, is a major threat to tobacco production in the US and other tobacco-producing areas worldwide. The development of race 1 and the resulting loss of the major source of single-gene resistance to the disease occurred rapidly throughout the tobacco producing areas of the US. The rapid shift from race 0 to race 1 in NC was documented in a statewide survey represented by samples from 76 tobacco fields in 23 counties. In addition to race, pathogen isolates obtained during this survey also were characterized for the phenotypic traits of mating type and mefenoxam sensitivity and then characterized by comparing sequences from 3 cytoplasmic and 2 nuclear regions. Both the A1 and A2 mating types were found throughout the state, with both mating types recovered from multiple fields. Pairings of isolates from within fields yielded viable oospores, indicating for the first time the potential for sexual sporulation by P. nicotianae in natural populations. Since the loss of complete resistance required a renewed use of the fungicide mefenoxam, a subset of the survey isolates were screened for sensitivity to the fungicide. All isolates were sensitive, with a mean EC50 of 0.4 μg/ml that was similar across mating types and races. Molecular characterization of the cytoplasmic and nuclear regions of 226 pathogen isolates revealed that the pathogen exists as multiple clonal types within the state. Some clonal types were present throughout the state while others were limited to certain geographic regions. The greatest diversity was observed in the mountain region of the state where the greatest number of fields with both mating types was present. The wide genetic diversity among the pathogen population and the newly discovered potential for sexual recombination may help explain the ability of the pathogen to rapidly adapt to host resistance genes.} }

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