Antimicrobial Activity of Five Plant Extracts and Synthetic Fungicide in the Management of Postharvest Pathogens of Yam (Dioscorea Rotundata Poir) in Storage

Crude extracts leaves of Azadirachta indica A. Juss. (neem), Nicotiana tabacum Linn. (Tobacco), rhizomes of Zingiber officinale Rosc. (Ginger), leaves of Carica papaya Lam. (pawpaw) and seeds of Piper guineense Schumach. (Black pepper) were tested at 30 g/L, 60 g/L and 90 g/L as well as mancozeb at 4 g/L, 8 g/L and 12 g/L concentrations against Aspergillus ochraceus in vitro. Rotted yam tubers were collected from farmers' barns forth nightly for four times.Treatments were replicated three times and completely randomized. Data were subjected to analysis of variance (ANOVA) and means were separated using Fisher's least significance difference (LSD). Mycelial growth of A. ochraceus was inhibited by these extracts. Percentage growth inhibitions at 30 g/L ranged from 40.19% (N. tabacum) to 51.95% (P.guineense) while percentage growth inhibitions at 60 g/L ranged between 57.47% (N. tabacum) and 70.56% (P. guineense). The highest inhibitions were recorded at 90 g/L with a range between 66.22% (A. indica) and 74.15% (P. guineense). Mancozeb was found to be the best in inhibiting the mycelial growth of A. ochraceus in culture irrespective of concentration and duration of incubation with 100% growth inhibition. The extracts and mancozeb were sprayed on yam tubers before storage for five months. Stored tubers showed a decay reduction index of 1.00 (mancozeb), 0.93 (A. indica) and 0.83 (P. guineense and Z. officinale) in the first year of storage indicating a reduction in rot by 100%, 93% and 83%, respectively. The extracts were comparatively less effective in the second year of storage. It is therefore, concluded that plant extracts could be used in management of rot causing organisms of yam in storage since they are environmentally safe, cheap and easily available compared with synthetic chemicals.