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Title:   Author  item
                                            SAVILLE, A - North Carolina State Universityitem
                                            Graham, Kimberlyitem
                                            Grunwald, Niklaus

                                                         - *Nik*item
                                            MYERS, K - Cornell Universityitem
                                            FRY, W - Cornell Universityitem
                                            RISTAINO, J - North Carolina State University
  Submitted to: Plant Disease
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/15/2015
                                    Publication  Date: 5/30/2015
                                    Citation: Saville, A., Graham, K., Grunwald, N.J., Myers, K., Fry, W.E., Ristaino, J.B. 2015. Fungicide sensitivity of US genotypes of Phytophthora infestans (Mont.) de Bary to six oomycete-targeted compounds. Plant Disease. 99:659-666.Interpretive Summary: Phytophthora infestans is the plant pathogen causing potato and tomato late blight. This pathogen is managed mostly by using fungicides. The US population of this pathogen consists of clones that differ by region and year sampled. Some clones are resistant to the fungicide mefenoxam, while others are not. The US-8 and US-11 clones were insensitive to mefenoxam while the US-20, US-21, US-23 and US-24 clones were sensitive to mefenoxam. We also tested sensitivity to other fungicides and found that the pathogen clones are sensitive to azoxystrobin, cyazofamid, cymoxanil, fluopicolide, or mandipropamid. This information is useful for management of potato and tomato late blight by growers.
                                Technical Abstract: Phytophthora infestans (Mont.) de Bary causes potato late blight, an important and costly disease of potato and tomato crops. The baseline sensitivity of recent clonal lineages of P. infestans was tested for six oomycete-targeted fungicides. Forty five isolates collected between 2004 and 2012 were tested in vitro on media amended with a range of concentrations of either azoxystrobin, cyazofamid, cymoxanil, fluopicolide, mandipropamid, or mefenoxam. Measurements of radial growth were used to generate dose-response curves and calculate EC50 values for each isolate. The US-8 and US-11 clonal lineages were insensitive to mefenoxam while the US-20, US-21, US-23 and US-24 clonal lineages were sensitive to mefenoxam. Insensitivity to azoxystrobin, cyazofamid, cymoxanil, fluopicolide, or mandipropamid was not detected among any lineage. Examination of disease outbreaks documented in USAblight revealed a rapid change in clonal lineages over time in the US and the displacement of the US-22 lineage by US-23, both of which are sensitive to mefenoxam. Neither the introduction nor development of insensitivity to mefenoxam in current US populations during the displacement of lineages was observed.


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