The susceptibility of different regions in Dioscorea rotundata (white yam) tuber to rot infecting fungi was investigated. Isolation was made from the periphery of the rotted tuber tissues, followed by a pathogenicity test and identification of isolates. Three fungi associated with D. rotundata (white yam) were isolated; they include Penicillium oxalicum, Aspergillus niger and Rhizopus stolonifer. Each of the isolates from pure cultures were inoculated on the head, middle and tail regions of healthy yam tubers. The three fungi were found to be pathogenic at different rates at the head, middle and tail ends of the yam tuber respectively. The head region was less susceptible to the three fungi with the following rot depths (P. oxalicum 25 mm a , A. niger 18.2 mm a and R. stolenifer 12.7 mm b ). Rot depth in the middle region was (P. oxalicum 15 mm a , A. niger 10.6 mm a and R. stolenifer 8.8 mm b ). While the tail region of the yam tuber recorded rot depth of (P. oxalicum 32.0 mm a , A. niger 26.4 mm a and R. stolenifer 20.8 mm b ) respectively. Generally, the tail region of D. rotundatawas more susceptible to fungal attack and the rot recorded in the tail region was significantly different from rot at the middle and the head. It was recommended that yam tubers should be stacked with their head on the ground to reduce incidence of rotting in stock-piled yam tubers.

Various yam species are cultivated but white yam (Dioscorea rotundata Poir.), water yam (Dioscorea alata L.) and yellow yam (Dioscorea cayenensis Lam.) are among the most cultivated in Nigeria. The Susceptibility of three tubers of Dioscorea species (D. rotundata, D. alata and D. cayenensis) to dry rot pathogens was investigated. Isolation was made from rotted tuber tissues, followed by pathogenicity test and identification of isolates; two fungal species Aspergillus niger and Rhizopus stolonifer were isolated and identified as the major fungi causing yam tuber dry rot in the study area. There was significant difference (P<0.05) in the susceptibility of the various Dioscorea tuber species studied to rot caused by Aspergillus niger [D. rotundata (20mm), D. alata (11mm) and D. cayenensis (3.5mm)] and  Rhizopus  stolonifer [ D. rotundata (17.5mm), D. alata (10mm) and D. cayenensis (2mm)]. The phytochemical contents of the three tubers of Dioscorea species examined also varied significantly, with the bioactive substances of D. cayenensis and D. alata relatively higher when compared to D. rotundata. Therefore, this research reveals that three metabolites; Saponin, Flavonoid and Tanin constitute the major trait for resistant ability of D. cayanesis and D. alata to dry rot causing pathogen.  Therefore, it is necessary that the differences in susceptibility be considered when developing yam barns. Also, researchers should work on genetically improving the susceptible white yam (D. rotundata) which is commonly eaten by millions of Nigerians with a possibility of increasing the quantities of the deficient phytochemicals.

The third world countries are not just suffering from food shortage, they are also plagued by malnutrition which stems from poverty coupled with inadequate informations about the nutritional contents of foods consume by most of her populace. Yam is a stable food consume by millions of Nigerians and the decision of which species to consume is often based on palatability and availability. Proximate analysis was carried out on D. rotundata., D. cayenensis and D. alata to compare their protein, carbohydrate, moisture, crude fibre, fat and ash content. The result reveals that Carbohydrate content of D. cayenensis (50.60%) was higher when compared to D. rotundata (48.8%) and D. alata (36.02%).  Also, the crude fibre of D. alata (5.26%) was significantly higher compared to D. cayenensis (4.86%) and D. rotundata (4.75%), similar result was obtained for the protein content of D. alata; which was 3.46% compared to D. cayanensis (2.13%) and D. rotundata (1.61%) respectively. This research concludes that the proximate composition of the Dioscorea species studied varied significantly. Yam consumers and nutritionist are advised to select their yam species in view of the various proximate constituents to achieve a well balance diet in terms of food and composite flour. The cultivation of the D. alata species should be encouraged because of its low Carbohydrate and high protein contents, thus making it suitable for diabetic patients or people suffering from related illnesses.