Blemishes of Table Potatoes:
Common Biotic Causes
By Jacquie van der Waals, Ph.D.
Department of Plant Science
University of Pretoria
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Potato tubers are affected by a number of blemishes, which can cause severe economic losses, in terms of rejection of seed batches, yield losses, downgrading of potatoes on the market, or rejection of processing potatoes. Despite the fact that many blemishes are merely cosmetic in nature, the demand by consumers for washed potatoes has exacerbated the problem of rejection of blemished tubers. Tuber blemishes are broadly classified as typical or atypical. Typical blemishes have known causes, for example pests, pathogens or specific abiotic factors; while the cause(s) of atypical blemishes have yet to be determined. Correct diagnosis of a tuber blemish is important in management of the disease and prevention of future occurrences of the blemish. This presentation covers the causal agents, symptoms and management of the most common typical tuber blemishes with biotic causes, and can serve as a guide for growers and others in the potato industry to help with identification of these blemishes.