Abstract
Alternaria blight (AB) of sweet potato ( Ipomoea batatas L.), caused by Alternaria spp., was recently reported in South Africa, but is common in southern and eastern Africa. Elsewhere in the world, AB is controlled primarily using resistant varieties. Twenty-five sweet potato varieties/breeding lines, from different origins were assessed for tolerance to AB. The materials were planted in fields having a history of AB disease and rated for tolerance based on a General Disease Index (GDI), with the lowest scores representing tolerance, and the higher scores representing susceptibility. Variety 199062-1 had the lowest GDI value, and was the most tolerant to AB; while W119 had the highest GDI value and was the most susceptible to the disease. Other varieties/breeding lines showed a variation in GDI values between most tolerant and most susceptible. Among the fungicides tested under field conditions, the mixture azoxystrobin-difenoconazole was the most effective in reducing AB intensity. Fungicides pyraclostrobin-boscalid, unizeb, azoxystrobin-chlorothalonil and cymoxanil-mancozeb were also effective against the disease. Key Words : Alternaria bataticola , General Disease Index, Ipomoea batatas
Highlights
Sweet potato (Ipomoea batatas L.) is the sixth most important food crop in the world, with 105 metric tonnes produced annually
The objective of this study was to evaluate a wide range of sweet potato varieties/breeding lines from different origins under field conditions for tolerance to Alternaria blight (AB), and screening for efficacy of selected fungicides against AB
High AB disease levels were naturally present at both field trial sites at the end of both growing seasons (Table 3)
Summary
Sweet potato (Ipomoea batatas L.) is the sixth most important food crop in the world, with 105 metric tonnes produced annually. Orange-fleshed sweet potato varieties are important for having a high betacarotene content, which helps to alleviate vitamin A deficiency in children, especially in rural areas of Kenya (Lopes and Boiteux, 1994; Mwanga and Ssemakula, 2001). Alternaria blight (AB) is a serious disease of sweet potato in Central, Eastern and Southern Africa (Van Bruggen, 1984; Anginyah et al, 2001; Kapinga and Carey, 2003; Osiru et al, 2007). In Uganda, AB is ranked the most important constraint to sweet potato production (Anginyah et al, 2001). Yamamoto has been observed to be the main causal pathogen (Lopes and Boiteux, 1994; Osiru et al, 2008) while A. alternata Fries (Anginyah et al, 2001) and A. capsici-annui Savul. and Sandu (Sivaprakasam et al.,1977) induce AB symptoms on sweet potato (Anginyah et al, 2001)
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