Discovery of new diseases of cassava in West Africa

Two new diseases of cassava were discovered in Benin, Ghana, and Nigeria. Curvularia leaf and stem blight [Curvularia lunata (Wakker) Boedijn] was discovered in all three countries. In the field, incidence of Curvularia-infected plants ranged between 0 and 80%, and severity between 2 and 25 lesions per plant. The effect of the fungus on growth was investigated using six cultivars, all naturally infected. For all cultivars, when buds were completely colonized, sprouting was completely inhibited. However, partially colonized buds sprouted, but growth was reduced by 20-50% (depending on genotype), compared with healthy stems. On artificially inoculated leaves, C. lunata induced lesions of up to 1.5 cm and 40% leaf abscission, compared with healthy leaves. Nattrassia mangiferae (Syd. & P. Syd.) B. Sutton & Dyke root and stem rot was discovered in Benin and Nigeria, with field incidence ranging between 0 and 54%. For all four cultivars, N. mangiferae significantly reduced the number of shoots, shoot growth, and number of roots. Two of the cultivars died three weeks after planting.