Etiology and control of common scab on potatoes in South Africa

Potato (Solanum tuberosum L.) is the world's fourth most important food crop after wheat (Triticum aestimum, L.), maize (Zea maize L.) and rice (Oryza sativa L.), and provides a balanced source of starch, vitamins and minerals to many communities in the global village (Rowe, 1993). Of all primary food crops, potatoes suffer the greatest losses due to disease (Agrios, 1997). ). Of the various diseases, common scab is one of the oldest and was first recorded in South Africa by Pole Evans (1906). Recent statistics indicate that 0.1 % of all seed potato tubers produced in South Africa are infected with common scab (http://www.potatoes.co.za). Between 1996 and 2001, the percentage of bags containing infected seed tubers averaged 32 %, with a corresponding rejection or desertification of the seed. The disease also reduces the cosmetic value of ware potatoes and, with the growing consumer-demand for blemish-free produce, increasingly results in the downgrading of consignments on the ware mark...