Impact of Tomato Grafts on the Potato Tuber Metabolome and Skin Colour

Grafting is a traditional research and crop production technique used to study the long-distance movement of molecules, reduce disease susceptibility, and improve yield, quality, and nutrient content. Tomato/potato grafts are rare examples of successful interspecies grafting, even resulting in commercially available products. Nevertheless, information on the effect of tomato on the quality parameters of potato tubers is scarce. In this study, the tomato cultivar ‘Mobil’ was grafted with the potato cultivars ‘White Lady’, ‘Hópehely’, and ‘Désirée’, and the phenotype, metabolite composition, and starch and protein contents of the tubers were analysed. Anthocyanins were isolated from the tuber skins, and the expression level of the transcription factor ANTHOCYANIN1 (StAN1) was evaluated. Out of the 112 identified metabolites, the concentrations of twelve compounds were altered in the same direction in all three cultivars. Compared to the self-grafted control, the starch content of tubers was increased in each cultivar, while the protein level remained unaltered in ‘White Lady’ and ‘Hópehely’. The oval tubers became roundish. The tomato scion increased the anthocyanin content of ‘Hópehely’ and ‘Désirée’ tuber skins, which was correlated with the upregulation of StAN1 expression. These results indicate that tomato scion has a significant impact on the quality parameters of potato tubers.