Efficacy of some plant extracts (Piper nigrum, Zingiber officinale, Azadirachta indica, Carica papya and Nicotiana tabacum) and a chemical fungicide (mancozeb) using three concentrations of hot aqueous plant extracts (30, 60 and 90 g/l) and mancozeb (4, 8 and 12 g/l) in in vitro inhibition of Colletotrichum sp. mycelia was carried out at Advanced Plant Pathology Laboratory, Federal University of Agriculture, Makurdi, Nigeria. Rotted yam tubers were collected from farmers’ barns and taken to the laboratory for isolation and identification of fungal organisms. Colletotrichum sp. was subsequently isolated and identified based on microscopic examination and its morphological characteristics from the pure culture of the fungus. 5 ml of each extract and the chemical fungicide were separately amended in 15 ml of potato dextrose agar and the pathogen was inoculated in the plates and incubated for 120 h and measurement of mycelia radial growths were recorded at 24 h interval throughout the period of incubation. The results obtained showed that all the plant extracts at all concentrations significantly (p<0.05) inhibited the mycelia growth of Colletotrichum sp. with the highest mean percentage growth inhibition recorded at concentration of 90 g/l followed by 60 g/l and 30 g/l. At 30 g/l, Z. officinale (60.69%) was more fungitoxic followed by P. nigrum (53.83%) compared with the least effective extract of C. papaya (30.39%). At 60 g/l, Z. officinale and A. indica both inhibited the mycelia of Colletotrichum sp. by 68.50% compared with the least inhibition of C. papaya at 43. 70%. At 90 g/l, P. nigrum was the most efficacious (82.19%) followed by Z. officinale (76.98%) while the least potent extract was C. papaya with an inhibition of 51.97%. The results showed that increase in period of incubation resulted in increase in percent growth inhibition with Z. officinale and P. nigrum been more effective at all concentrations compare with extracts of A. indica, N. tabacum and C. papaya. The chemical fungicide consistently gave 100% inhibition irrespective of concentration or duration of incubation. It is therefore concluded that all the plant extracts posses’ antifungal compounds and should be used to control fungal rots of yam since extracts of plants are eco-friendly, cheap and easily available.
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