Powdery Scab of Potato: A Diagnostic Guide

Powdery scab, caused by Spongospora subterranea, is a soil- and tuber-borne disease of potato. The fungus-like protozoan pathogen can be found around the world and in almost every large potato-producing state across the United States. Initial signs of infection in the eyes and lenticels of tubers are slightly sunken, purple-brown lesions. When a tuber lesion reaches maturity, the periderm bursts, releasing masses of tiny, powdery balls. The objective of this diagnostic guide is to provide detailed information on the isolation, sampling, pathogenicity testing, and detection of the pathogen in the soil and tubers using classical and molecular techniques to facilitate the identification of the disease in the laboratory and field.