Protein and sugar content of tubers in potato plants treated with biostimulants

The use of biostimulants and cultivar selection play an important role in modern potato farming because they influence tuber yield and quality. The nutritional value and processing suitability of potato tubers are affected by their content of total protein, reducing sugars and sucrose. The aim of this study was to determine the effect of biostimulants on the content of total protein, glucose, fructose and sucrose in potato tubers (skin, flesh and whole tubers with skin), at harvest and after 5 months of storage. The experimental materials included tubers of five edible potato cultivars: Irga, Satina, Valfi, Blaue St. Galler and HB Red. Dur- ing the growing season, potato plants were treated with the following biostimulants: Asahi SL, Bio-Algeen S-90, Kelpak SL and Trifender WP. Control plants were not treated with biostimulants. The total protein content of tubers was determined by the Kjeldahl method. Simple sugars and sucrose were determined by high-performance liquid chromatography. At harvest, total protein concentration was significantly higher in purple- and red-fleshed cultivars than in cream- and yellow-fleshed cultivars. An analysis of tuber parts revealed that flesh had the highest protein content. The total protein content of tubers increased during storage. Biostimulants had no significant effect on total protein concentration in tubers at harvest or after storage. The content of simple sugars and sucrose was higher in the skin, flesh and whole tubers of purple- and red-fleshed cultivars, than in cream- and yellow-fleshed cultivars. Potato tubers with colored flesh accumulated the highest amounts of total sugars. Biostimulants, in particular Bio-Algeen S-90 and Kelpak SL, contributed to the accumulation of monosaccharides and the disaccharide in potato tubers, and, in conse- quence, total sugars. Their concentrations in potato tubers increased during storage.