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Poster: Biology & Disease Mgmt: Chemical Control


Assessment of acquired resistance of originally sensitive isolates of Phytophthora infestans to the systemic fungicides fluopicolide and propamocarb
J. GONZÁLEZ-TOBÓN (1), J. Chirivi-Salomon (1), M. Parra-Bastidas (1), R. Childers (2), S. Restrepo (1), G. Danies (1) (1) Universidad de los Andes, Colombia; (2) Harvard University, U.S.A.

Phytophthora infestans, a plant pathogenic oomycete, is the causal agent of late blight disease of potatoes and tomatoes. This disease causes devastating economical losses each year and control is mainly achieved by the use of fungicides. Previous studies have reported that sensitive isolates to the phenylamide fungicide, mefenoxam, become tolerant after a single passage on mefenoxam-containing medium. The acquired resistance of the sensitive isolates appeared to have a cost on the rate of mycelial growth and declined slightly with subsequent culturing on medium free of mefenoxam. The aim of this study was to investigate whether the same phenomenon is observed using two different systemic fungicides: fluopicolide and propamocarb. Susceptible isolates of P. infestans were exposed to three different concentrations of fungicide-amended medium: 0, 5, and 10 µg ml-1 for fluopicolide and 0, 1 and 100 µg ml-1 for propamocarb. To assess if the isolates had acquired resistance to each of the fungicides tested, mycelia from isolates growing at 5 µg ml-1 for fluopicolide and 1 µg ml-1 for propamocarb were transferred once again to media with the same concentrations mentioned above. This study provides further insights into the in vitro adaptability of P. infestans against antifungal stress.