Purplish-brown pustules, usually circular, of 0.2 to 5 mm in diameter, but sometime wider and deeper, initially developping on tuber surface and extending under the periderm to form raised lesions
The lesions become filled up with a dry, powdery mass of sporeballs At maturity, these lesions release the spore balls and become partly or entirely empty
As pustule bursts and reveals powdery sporeballs, small flaps of loose skin remain at the edge of the lesion
Sometime, atypical symptoms with brown necrotic tissues may be observed under the periderm
Lesions can expand in both directions, depth and width, to form deeply eroded cankers and outgrowths that induce mishapened tubers
Roots and stolons of the plant can be infected leading to the development of white galls (turning black when exposed to the air) of 1 to 10 mm in diameter
Place the powder scraped from the lesions on a microscope slide with cotton blue, and observe the presence of typical sporeballs, at 10 and 40X magnification.
