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Revista Chapingo. Serie horticultura

On-line version ISSN 2007-4034Print version ISSN 1027-152X


LOZOYA-SALDANA, Héctor et al. Sensitivity to fungicides of Phytophthora infestans (Mont.) de Bary in Chapingo, Mexico. Rev. Chapingo Ser.Hortic [online]. 2017, vol.23, n.3, pp.175-187. ISSN 2007-4034.

Chemical control of plant diseases exerts high selection pressure for the development of pathogen resistance to fungicides. The objectives of this study were to quantify the existence of late blight in Solanum tuberosum L., detect the presence of variants of the oomycete resistant to agrochemicals and compare the different levels of resistance in the isolates from one cycle to another. Plots of the potato cv. Fianna, susceptible to late blight (Phytophthora infestans [Mont] de Bary), were exposed to natural infection of the pathogen to detect the presence of variants of the oomycete resistant to the agrochemicals from one cycle to another, and from in vivo with respect to in vitro conditions, by applying a half dose of fungicides. The disease reached 100 % final foliar infection in treatments with ciazofamid in 2011 and with fosetyl-Al in 2012. On the other hand, mandipropamid allowed only 21-22 % infection in both years in the field. However, 49 % of the P. infestans population was susceptible, 39 % was intermediate, and 19 % was resistant to this product in vitro. Plots treated with fosetyl-Al reached 80-100 % infection in the field, while in vitro 88 and 46 % of the P. infestans populations showed intermediate resistance when exposed to high dosages of the product, and 62 % were resistant at low dosage. Isolates from field plots with natural infection exposed to ciazofamid were all sensitive in vitro. The inconsistencies of the oomycete regarding fungicide resistance/sensitivity under in vivo/in vitro conditions, as well from one year to another, do not support behavior predictability. These results expose the great genetic plasticity of the oomycete in relation to its sensitivity to fungicides.

Keywords : late blight; potato; Solanum tuberosum; fungicide resistance.

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