A disease survey of Fusarium wilt and Alternaria blight on sweet potato in South Africa

A disease survey was conducted on sweet potato in the major production areas of South Africa in 2006-2008 to determine the importance of wilt disease (WD) and Alternaria blight (AB) caused by Alternaria bataticola. The disease prevalence, incidence and severity were assessed for both WD and AB in 58 sweet potato fields in seven provinces, and included both commercial and resource-poor growers. The prevalence of WD in commercial fields was significantly higher than in resource-poor fields; while disease incidence and severity were very low in both commercial and resource-poor fields. Soil pH showed a moderate negative linear correlation to WD severity. WD is at present considered a minor disease of sweet potato in South Africa, although local outbreaks can be damaging. AB had very low disease prevalence, incidence and severity levels in both commercial and resource-poor fields countrywide. However, one of the fields had moderately high disease incidence and severity levels, showing that the disease can be destructive if not controlled. AB should be considered a potentially destructive disease of sweet potato in South Africa. Fusarium oxysporum was consistently isolated from WD plants, with F. oxysporum f. sp. batatas identified, but other formae speciales were also associated with the disease.