In this study, eight transformed Solanum tuberosum L. plants, affected in their nitrate assimilatory pathway by the introduction of a tobacco nitrate reductase gene (Nia2), were cultivated in glasshouse conditions at INRA Ploudaniel (West Brittany, France). Two irrigation regimes were compared and plants were sampled at four stages of vegetation. Yield, tuber dry matter content, total nitrogen content, nitrate content in the whole plant, and nitrate reductase activities were studied. High frequency irrigation with nutritive solutions negatively affects both yield and dry matter content in tubers. Moreover, the introduction of the tobacco Nia2 gene in the potato genome does not seem to affect the agronomical parameters of the initial genotype apart from the nitrate content of tubers. Five transgenic genotypes out of eight, in fact, showed a drastic decrease (of around 98%) in their tuber nitrate content. This nitrate decrease in the tubers was also correlated with the presence of the mRNA transgene, whereas the potato nitrate reductase transcript does not seem to be expressed in wild-type tubers. Regarding these genotypes, developmental stage and nutritive solution supply were found to have no effect on tuber nitrate content. In fact, tubers derived from these clones exhibited low nitrate content throughout the vegetation period, while nitrate accumulation in wild-type tubers is progressive and increases sharply with high nutritive solution supply.
