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Characterization of Phytophthora infestans populations from soils of the Ecuadorian Andes

Maria Soledad Benitez Ponce: The Ohio State University

<div>Potato late blight is a major concern for potato production in all regions of the world. In Ecuador, the incidence of foliage infection is high and can severely compromise potato production. Tuber blight, however, is low, which has been attributed to suppressive characteristics of soils where potatoes are produced. Inoculum for tuber infection often comes from infected foliage residue and infected seed tubers. In this work, we characterized populations of <em>Phytophthora infestans</em> in soils as a way to understand incidence and infectivity of soilborne inoculum for tuber infection. Sixty-one isolates were obtained directly from soils from potato-growing fields of two provinces in Ecuador representing the major potato growing regions in the Ecuadorian Andes. Sampling design considered field topography, host developmental stage and soil depth. Greater number of isolates were recovered at a shallower depth and at flowering. All isolates collected were infective in both leaf and tuber assays. Mitochondrial DNA analysis indicated the presence of haplotypes Ia, Ib and IIb and IIa, and suggested the occurrence of clonal lineages EC-3, US-1, EC-1 and US-6, and mating type A1. Furthermore, microsatellite analyses revealed significant population differentiation between provinces. There was no correlation between haplotype, genetic variation and infectivity. These results confirm inoculum pathogenicity, further confirming the suppressive nature of Ecuadorian soils to tuber blight.</div>