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. During 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 consequence, total sugars. Their concentrations in potato tubers increased during storage.

Experiment was conducted twice: in spring of 1999 and 2000. Two greenhouse cucumber varieties (Aramis and Corona) with different susceptibility to spider mires were employed to compare the harmfulness of the two-spotted spider mite and the carmine spider mite. Effects of the rwo-spotted spider mite and the carmine spider mite feeding either on the fruit production or on the content of some organic compounds were measured. Moreover, development of spatially separated populations of the two-spotted spider mite and the carmine spider mite was analysed. Two abiotic parameters were taken into account: temperature and sunlight duration. Increment of the carmine spider mite population density was faster during the season of higher temperature and sunlight duration (spring of 2000). Differences in the development of rwo-spotted spider mite were not observed. The increase of fruit weight was closely correlated with increase of densiry of spider mires. The feeding of relatively low populations of the carmine spider mite (up to 5-7 mobile stages per leaf) stimulated the weight increase of fruits collected from Aramis and Corona varieties. The feeding of rwo-spotted spider mite and the carmine spider mire affected the distribution of organic compounds produced in plants. In quire severely infested leaves (2-3 damage level of De Ponti scale) rota! amount of sugars and phenolic compounds increased as compared ro control leaves.