Quinoa is an expanding crop in southern Spain. Downy mildew, caused by Peronospora variabilis, is the most important quinoa disease in Spain and worldwide. In Spain, this disease has also been observed on the weed Chenopodium album. The objectives of this study were to unravel the origin of the P. variabilis isolates currently infecting quinoa in southern Spain and to study their genetic diversity. We hypothesized that P. variabilis isolates infecting quinoa in Spain could have been introduced through the seeds of the quinoa varieties currently grown in the country or, alternatively, that these isolates are endemic isolates, originally infecting C. album, that jumped to quinoa. In order to test these hypotheses, we sequenced the internal transcribed spacer (ITS), cytochrome c oxidase subunit 1 (cox1), and cox2 regions of 33 P. variabilis isolates infecting C. quinoa and C. album in southern Spain and analyzed their phylogenetic relationship with isolates present in other countries infecting Chenopodium spp. cox1 gene sequences from all of the Spanish P. variabilis isolates were identical and exhibited nine single-nucleotide polymorphisms (SNPs) compared with a single P. variabilis cox1 sequence found at GenBank. Phylogenetic analyses based on the ITS ribosomal DNA region were not suitable to differentiate isolates according to their geographical origin or host. The cox2 sequences from P. variabilis Spanish isolates collected from C. quinoa and C. album were all identical and had a distinctive SNP in the last of four polymorphic sites that distinguished Spanish isolates from isolates from other countries. These results suggest that P. variabilis infecting quinoa in southern Spain could be native isolates that originally infected C. album.[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
Keywords: Chenopodium album; Chenopodium quinoa; Peronospora variabilis; genetic diversity; quinoa downy mildew.