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In vitro and in planta assessment of the effect of mefenoxam-acquired resistance on sporulation in isolates of Phytophthora infestans

Melissa Regnier: Universidad de los Andes

<div><em>Phytophthora infestans</em> is an oomycete pathogen that causes potato and tomato late blight disease, a worldwide concern for farmers given its explosive epidemic potential. In order to control the disease, an integral management approach, which includes the use of fungicides, has been implemented. Unfortunately, populations of <em>P. infestans</em> resistant to fungicides have been documented. Furthermore, studies have shown that isolates of <em>P. infestans</em> are able to acquire resistance to mefenoxam <em>in vitro</em>, after a single exposure through sub-lethal concentrations of this widely used fungicide. The aim of this study was to evaluate if there is an effect on sporangial production in isolates of <em>P. infestans</em> that acquire resistance to mefenoxam <em>in vitro</em>. An originally susceptible isolate of<em> P. infestans</em> was exposed to different concentrations of mefenoxam-amended media and compared to a resistant control. Sporangia production was significantly diminished in isolates that acquired resistance. Interestingly, naturally resistant isolates sporulated significantly more in the presence of mefenoxam. Possible implications of the acquisition of resistance on sporangia production are discussed. These results provide further insights into the phenomenon of mefenoxam-acquired resistance.</div>