Decreasing NPK doses, less than the recommended one, decreased chlorophylls a, b and their total as well as reducing sugars, non-reducing sugars and total carbohydrates, whereas carotenoieds and poly saccharides were increased during the two growing seasons. Chlorophyll a/b as well as total chlorophylls/ carotenoides ratios were also increased due to NPK stresses. Application of bio-fertilizers, over all the NPK minerals doses, improved the accumulation of all photosynthetic pigments fraction as well as reducing sugars, non-reducing sugars, total sugars and total carbohydrates whereas, decreased that of polysaccharides compared to the plants grown without bio-fertilizers inoculation.  Similarly, chlorophyll a/ chlorophyll b and chlorophylls /carotenoides ratios were increased with the same manner due to the inoculation of bio fertilizers used. The application of NFB was more effective than the other strains used followed by PDB and SB when used individually or incombinations compared with plants inoculated without bio fertilizers. The interaction treatments between minerals and bio fertilizers, show that, bio fertilizers counteracted the depressing effects of decreasing NPK dose less than the recommended one on all photosynthetic pigments as well as reducing, non-reducing and total sugars as well as total carbohydrates whereas, decreased insoluble  carbohydrates in   the shoot systemof potato plants during  the two growing seasons. An additive effects were recorded in plants grown in 100% NPK and inoculated with bio-fertilizers mixture. Again, NFB strain was most effective than the other strains if inoculated individually or in combination with the others. Application of 75% NPK combined with bio fertilizers showed high values in this respect. The most effective treatment was found with NFB+PDB+SB followed by NFB+PDB and NFB+SB respectively. Generally, it seems that all bio-fertilizers used, with the superiority of NFB strain, counteracted the depressing effect of NPK decreases on photosynthetic capacity up to 75% dose.  At 75% NPK dose combined with bio-fertilizers attained nearly similar results with those recorded in the control plant. On the other, bio-fertilizers used failed to counteracted  the harmful effects of NPK at 50% dose from the recommended dose. Bio-fertilizers in the presence of NPK at 50% dose from the recommended dose attained the minimum values in this respect.