Superficial, circular necrotic lesions develop on cultivar Ramacimiento (Solanum tuberosum ssp.andigena) tubers in plantings at elevations above 2,500 m in the Peruvian Andes. After drying or storage the lesions become sunken or cankerous. A virus was transmitted mechanically toChenopodium quinoa andC. amaranticolor with leaf and fruit saps from Renacimiento plants grown from symptomed tubers. The virus is a strain of potato mop-top virus which causes milder tuber symptoms in European cultivars.C. quinoa was better thanC. amaranticolor as an indicator host; its spreading local lesion reaction was most sensitive at 15 C, less at 10 and 20, and nil at 25 C. Sap inoculum from fruit resulted in symptoms in 7 days, that from leaves in 13 days, and that from tubers produced no symptoms.