Pathogenicity of fungi associated with leaf spot disease of sweet potato (Ipomea batatas L. (Lam) in Makurdi, Benue State, Nigeria.

The screen house experiment was conducted to determine the pathogenicity of leaf spot fungi of sweet potato in Makurdi situated in the Southern Guinea Savannah of Nigeria. The experiment was a completely randomized design with twelve replicates. The variability in pathogenicity of four leaf spot fungi namely: Aspergillus flavus (Link), Aspergillus tamarii (Kita), Macrophomina phaseolina (Tassi),  and  Fusarium verticillioides (Sacc.) on sweet potato   variety  TIS-3164 was evaluated in the screen house using the spore suspension of the fungi at 15x 10⁶  spores/ ml on four weeks old plants. All four isolates were pathogenic and induced necrotic symptoms on sweet potato plants. The leaf spot lesions  were  widest  in sweet potato plants inoculated with A. tamarii (9 cm) followed by F. verticollioides (5 cm), A. flavus (4 cm) and M. phaseolina (3.20 cm). Sweet potato plants inoculated with spore suspension of the test fungi recorded significantly (P < 0.05) lower number of leaves with sweet potato plants inoculated with F. verticillioides recording the least number of leaves (30.75). At 4weeks after planting (WAP), the application of the spore suspension of A. tamarii produced significantly lower leaf area of 5.56cm². At 4 weeks after inoculation (WAI), percentage leaf defoliation was highest on sweet potato plants inoculated with A. flavus (44.50 %) and least when sweet potato plants were inoculated with M. phaseolina (34.30 %). The inoculation of the sweet potato plants with all test fungi had no significant effect on the vine length. The study demonstrated the pathogenicity of all four test fungi on sweet potato.