Correlation between mean protein spot intensity and reducing sugar content (RSC) in 40 cultivars without cold treatment. (A) Representative pattern of tuber proteins obtained by 2D-PAGE. Numbered arrows point to the five spots with significant correlation between mean spot intensity and RSC (Table 1). (B-F) Correlation plots of the logarithmic values of mean spot intensity versus RSC. Plots B, C, D, E and F correspond to spots 1, 2, 3, 4 and 5, respectively. Framed numbers indicate potato cultivars listed in Additional file 1: Table S1.