ABSTRACT

Antifungal effect of crude extracts of pods of Tetrapleura tetraptera and seeds of Carica papaya and Picralima nitida were determined in vitro on fungi pathogens that cause rot of cassava tubers. Samples of cassava with root-rot were used. The medium that was used is Potato Dextrose Agar (PDA). Chloramphenical at a concentration of 0.05mg/ml was incorporated to the media. The samples of rotted cassava tubers were cultured at 27C for 7days. Fungal isolates were identified. Mancozeb a synthetic chemical fungicide was also used as the positive control. Aspergillus niger, Colletotrichum species and Penicillium vanoranjei were isolated as the possible causative organisms. The pathogenicity of the isolated fungi were determined. I ml of 25, 50, 75 and 1 OOg of crude extracts of the three different plant extracts were used. Each treatment had three replicates. The percentage concentration inhibition was calculated. The antifungal activity varied with the extract and concentration. In some extracts the antifungal activity increased with increase in concentration while in other extracts the antifungal activity increased with decrease in concentration. On the mycelial growth of A. niger, C. papaya extract showed the inhibition of 61.1%, 60%, 63.3% and 64.4%, P. nitida extract showed the inhibition of 66.1%, 63.3%, 66.1% and 61.1% while T, tetraptera showed 66.1%, 64.4%, 50% and 56.1%. On the mycelial growth of Colletotrichum species, C. papaya extract showed the inhibition of 64%, 45%, 35% and 25%, P. nitida showed 63%, 60%, 54% and 26% and T. tetraptera showed 2.5%, 5.7%, 17% and 59%. On the mycelial growth of P. vanoranjei, C. papaya extract showed inhibition of 5%, 8.3%, 15% and 40%; P. nitida showed inhibition of 21%, 27.1%, 43.3% and 45% while T. tetraptera showed inhibition of 42%, 45%, 45% and 57.1%, all plant extracts at 2.5%, 5.0%, 7.5% and 10% ix concentration respectively. Comparing mancozeb and the three plant extracts, mancozeb showed more effective inhibition on the radial mycelial growth of all the tested fungi pathogens with 73.3% in A. niger, 78.0% in Colletotrichum species and 70% in P. vanoranjei. However, the study showed that C. papaya, P. nitida and T. tetraptera have the potential to control post harvest rot of cassava tubers. At all concentration extract of P. nitida showed the highest inhibition on mycelia growth in Aspergillus niger (64.1%) while C. papaya was 62.2%. Specifically, extract of P. nitida was more effective in inhibiting growth of the fungal isolates and Aspergillus niger was found to be the most sensitive to the extracts.