Tubers of white yam (Dioscorea rotundata Poir) obtained in three markets in Calabar, Cross River State, Nigeria, were found associated with seven microbial pathogens causing dry and wet rot of tissues. The pathogens included; Aspergillus niger, Penicillium expansum, Fusarium oxysporum, Botryodiplodia theobromae, Penicillium sclerotigenum, Fusarium moniliformes, and Rhizopus stolonifer. Of these A. niger, P. expansum, F. oxysporium and B. theobromae were highly pathogenic causing extensive tissue rot compared to the last three. Botryodiplodia theobromae effected an appreciable reduction in the amounts of nutrients in the head, middle and tail portions of yam tested within the five-week span of the experiment. One week after inoculation, there was a decline in the carbohydrate content from 34.80mg/100g dry weight in the control samples to 24.60mg, 25.10mg and 23.90mg in the head, middle and tail portions respectively. These values fell to 16.90 and 16.80mg/100g by the fifth week in the middle and tail portions respectively. Protein recorded a slight depreciation after one week of inoculation. This was followed by appreciable increment between week two and four (from 5.25mg/100g to 9.19mg/100g in the tail portion) and then a slight drop one week thereafter. The lipid content of the three portions tested recorded a steady decline throughout the period of the experiment. Amount of oxalate increased steadily in the inoculated tubers within the period of the experiment.
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