THE GLYCOALKALOID CONTENT IN POTATO-TUBER S (SOLANUM-TUBEROSUM L.) ASAFFECTED BY CULTIVATION TECHNOLOGY AND MECHANICAL DAMAGE

In the years 1994 to 1996 the field trial with three potato varieties (Krystala, Karin, Arnika) was carried out to study the varietal differ ences, effects of the year, some methods of cultural practices, mechan ical damage and length of storage on the content of alpha-chaconin and alpha-solanine. To determine amounts of the given glycoalkaloids (GA) the HPLC method as modified by Kobayashi et al. (1989) with respect t o experience of Kvasnicka et al. (1994) was used in the trial. It was found that the year has greater effect on GA content than the variety (Fig. 1). In 1994 a great precipitation deficit together with high tem peratures and length of sunshine were probably a reason of high GA con tents. Significant differences among varieties (Tab. I) witness to the possibility of selection of newly approved varieties by the GA conten t. Mechanical damage of tubers increased highly significantly the tota l GA content (more than double) compared with undamaged tubers in all three varieties (Tab. II). Damage was probably responsible for initiat ion of GA synthesis in stressed tissues of tubers. In two varieties af ter the damage of tubers a limit value of 200 mg.kg(-1) GA in fresh we ight of tubers was exceeded. Varietal differences in response to damag e of tubers by increased GA content indicate the possibility of select ion of clones with lower increase of GA content after damage of tubers . Sometime increasing nitrogen doses induced an increased alpha-chacon in as well as alpha-solanine content in tubers (Fig. 2). Addition of m olybdenum did not reduce the produced amount of GA. Post-emergently ap plied herbicide and chemical protection against potato late blight did not give unambiguous results compared with mechanical cultivation or treatment without protection against potato late blight in different y ears (Tabs III and IV). Results of the trial showed that there is no r eason to be afraid of increase of GA content above the limit 200 mg.kg (-1) when chemical preparations against weeds and for protection again st potato late blight. GA content increased in the first five months d uring storage, in further three months it was reduced to almost initia l values (Tab. V). Differences in GA content were not significant in t ubers in samplings during storage.