Etiology, incidence, and severity of downy mildew infecting quinoa crops in Cauca, Colombia

Downy mildew, caused by Peronospora variabilis, is one of the most limiting diseases affecting quinoa (Chenopodium quinoa) cultivation worldwide. In Colombia, there are few studies on this pathosystem. Therefore, the objective of this research was to determine the etiology, incidence, and severity of downy mildew in quinoa-producing areas in the department of Cauca. Commercial crops in the municipalities of Bolívar, La Vega, Silvia, and Totoró were visited to determine the incidence and severity of the disease, and symptomatic tissue samples were collected for studying the causal agent. The pathogen was morphologically identified using taxonomic keys and confirmed through phylogenetic analysis of the ITS and COX regions. To validate Koch’s postulates, inoculations were performed using a sporangiospore suspension on healthy quinoa leaf tissue. Downy mildew was detected in all four municipalities, with incidence ranging from 3.3% to 96.7% and severity between 0.8% and 66.3%. Morphometric and molecular analyses confirmed the identity of P. variabilis. Pathogenicity was verified 10 days after inoculation by observing symptoms and signs on the tissue. This study presents the first confirmed report of downy mildew caused by P. variabilis in quinoa crops in Colombia.