First report of Peronospora variabilis causing downy mildew disease in cañahua (Chenopodium pallidicaule) in Bolivia

Abstract Cañahua (Chenopodium pallidicaule Aellen) is a semi-domesticated grain cultivated in the Andean highlands for millennia. Cañahua seeds have high nutritional value and it has become attractive because of its high resistance to frost, drought and saline soils. In May 2018, cañahua plants showed symptoms of the downy mildew disease caused by Peronospora variabilis which is known to heavily affect its tetraploid-relative quinoa. Besides the typical symptoms in the plant, visual confirmation of P. variabilis reproductive structures by microscopy was achieved. In order to verify the ability of P. variabilis to infect cañahua, an artificial infection in three cañahua varieties was performed. The three cañahua varieties were infected by P. variabilis and developed downy mildew disease symptoms. The pathogen identity was confirmed by PCR and Sanger sequencing of the PvCox2 and PvITS region. DNA sequence identification confirmed that the P. variabilis that usually infects quinoa can also infect cañahua plants. Therefore, cañahua when grown next to quinoa must be carefully watched for downy mildew disease symptoms because P. variabilis can be a potential threat for future large scale cañahua agriculture.