Molecular characterization of Peronospora variabilis isolates infecting Chenopodium quinoa and Chenopodium album in Spain.

Abstract

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 oin 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 ITS, cox1 and cox2 regions of 33 P. variabilis isolates infecting C. quinoa and C. album in Southern Spain and analysed their phylogenetic relationship with isolates present in other countries infecting Chenopodium spp. cox1 gene sequences from all the Spanish P. variabilis isolates were identical and exhibited 9 SNPs compared to a single P. variabilis cox1 sequence found at GenBank. Phylogenetic analyses based on ITS rDNA region were not suitable to differentiate isolates according to their geographical origin or host. 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 infecting originally C. album.