Effects of Species of Yam (Dioscorea Species) and Fungal Pathogens on the Postharvest Behaviour of Yam Tuber in Nsukka Area of South Eastern Nigeria

Experiments were conducted at the plant pathology laboratory and improved yam barn of the University of Nigeria, Nsukka (UNN) to identify and characterize rot-causing organisms and asses the effects of species and these organisms on the post-harvest behaviour of yam in Nsukka area of southeastern Nigeria. Some fungal micro-organisms were isolated from decaying yam tuber obtained from yam dealers at Nsukka main market and cultured in a growing medium, sabouraud dextrose agar. Three isolates were characterized and identified as Aspergillius niger, Botryodiplodia theobromae and Fusairum oxysporum. Two species of yam, D. rotundata and D. alata, freshly harvested, were obtained from the Root and Tuber crops unit of the Department of Crop Science, UNN sterilized in 75% alcohol and rinsed with deionized water. . Lacerations (slits) were made with sterile inoculation needle on each of the clean tubers. A 1 ml spore suspension of each of the fungal isolates was inoculated into the slits on the tubers. The slits were then covered with a sterile cotton wool and both the inoculated and un-inoculated (control) samples were taken to the improved yam barn where the tubers were placed on wooden shelves for storage and observations. Parameters measured were infection severity, dormancy period, sprout vigour, rot colour and rot type. The two species of yam varied significantly (< 0.05) in infection severity, dormancy period, sprout vigour and weight loss. Similarly, the pathogens varied significantly in their activities on the stored yams with A . niger being the most virulent. The major finding in this study was that D. alata appeared less susceptible to fungal attack than D. rotundata. Breeders are advised to work towards isolating the traits in D. alata species for resistance and inject into other species of yam especially D. rotundata.