Two Pythium spp. were isolated from diseased tubers exhibiting rots at harvest, in summer stores and also in refrigerated storage. Symptoms shared features described for both pink rot caused by Phytophthora erythroseptica and leak caused by Pythium spp. The causal agents were identified as Pythium aphanidermatum and P. ultimum by morphological and physiological observations and by fingerprinting using oomycete specific primers to amplify the internal transcribed spacer (ITS1)within ribosomal DNAs. The optimum temperatures for infection were 30°C for P. aphanidermatum and 25°C for P. ultimum, corresponding to the optimum temperatures for growth in vitro. The optimum concentration for infection of tubers inoculated by dipping in a suspension of oospores or hyphal swellings after wounding was found to be 103 reproductive organs/ml, whereas the infection threshold was 10 reproductive organs/ml.