Calcium Biofortification in Potato: Impacts on Photosynthetic Performance, Tuber Calcium Content, and Calcium Distribution in Two Commercial Cultivars

Potato (Solanum tuberosum L.) is an important global food crop, being greatly valued for its high carbohydrate content and nutritional profile. In response to the world population’s rapid growth and the increasing need for nutritionally enhanced food quality, potato biofortification has become a key focus of agronomic research. This study investigated the effect of calcium (Ca) biofortification on two potato cultivars (Picasso and Rossi) cultivated in Portugal, assessing its impact on the photosynthetic functioning and the Ca content and distribution of tubers. At the beginning of the tuberization stage, seven foliar applications of CaCl2 or Ca-EDTA at 12 kg ha−1 were performed. The application of Ca-EDTA led to an increased Ca content in peeled tubers of Picasso (37%) and Rossi (16%), and 88% and 79% in unpeeled tubers, in the same cv. order and as compared to their controls, with Ca predominantly accumulating in the epidermis/peel region. Photosynthetic performance was negatively impacted by the Ca-EDTA treatment in Picasso but not in Rossi, which was reflected in the significant declines in net photosynthesis (Pn) and maximal (Fv/Fm) and actual (Fv′/Fm) photochemical efficiency of photosystem II. Additionally, both genotypes showed negative impacts (greater in Picasso) on the quantum yield of non-cyclic electron transport (Y(II)) and photochemical quenching (qL) after five foliar applications. This contrasted with the absence of negative impacts under the use of CaCl2, which resulted in 17.1% (Picasso) and 29.5% (RFossi) increase in Ca content in peeled tubers, without any significant differences between the unpeeled tubers of both cvs. Moreover, only with CaCl2, the tuber weight and yield were not negatively impacted. These findings pointed out that, although with a lower Ca increase in the tubers, CaCl2 was the best suitable option for the Ca biofortification of these cvs. at the applied doses.