Available online at www.pelagiaresearchlibrary.com Pelagia Research Library Asian Journal of Plant Science and Research, 2017, 7(2):8-16 ISSN : 2249-7412 CODEN (USA): AJPSKY Pelagia Research Library 8 Eficacy of Some Plant Extracts in In Vitro Control of Colletotrichum Species, Causal Agent of Yam (Dioscorea rotundata Poir) Tuber Rot Gwa VI 1,2* and Nwankiti AO 1 1 Department of Crop and Environmental Protection, Federal University of Agriculture, PMB 2373 Makurdi, Nigeria 2 Department of Crop Production and Protection, Faculty of Agriculture and Agricultural Technology, Federal University, Dutsin- Ma, PMB 5001, Katsina State, Nigeria ABSTRACT Eficacy of some plant extracts (Piper nigrum, Zingiber oficinale, 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 identiication of fungal organisms. Colletotrichum sp. was subsequently isolated and identiied 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 signiicantly (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. oficinale (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. oficinale 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 eficacious (82.19%) followed by Z. oficinale (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. oficinale 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. Keywords: Eicacy, In vitro, Plant extracts, Colletotrichum sp., Inhibition, Yam Rot INTRODUCTION Yams (Dioscorea spp.) are among the oldest recorded food crops and constitute an economically important staple for millions of people in the tropics and sub tropics. West Africa is the largest producer of this crop accounting for about 95% of total world production and 93% of the total yam production area [1]. Nigeria is the largest producer of the crop, producing about 38.92 million metric tonnes annually [2,3]. In spite of the high volume of production, the demand for yam tubers has always exceeded its supply due to the presence of rot causing organisms. Rot is a major factor limiting the Post-harvest life of yams [4,5] and losses can be very high resulting to seven million metric tonnes