Studies were carried out in 2003-2005 on the soil in South-Eastern Poland. The experiment was made by randomised blocks in there replications. The factor of the experiment was the cultivars of sweet potato: Carmen Rubin, Goldstar and White Triumph. Full manuring and uniform mineral fertilization were applied in identical amounts: 100 kg N, 43.6 kg P, 124.5 kg K and 25 t·ha⁻¹ FYM. The reproduction material comprised seedlings produced due to in vitro micropropagation. Samples for qualitative examinations (20 potato tubers of mean size) from three field replications for each plot were collected by standard methods. The differences in darkening of raw and coked sweet potato tubers was conditioned by the phenotypical variability.