The Effect of Light Exposures on the Content of Harmful Substances in Edible Potato Tuber

Background: The impact of light on the content of undesirable substances is particularly important in the case of potatoes available in store where the tubers are exposed to continuous light access. Both washed and unwashed potatoes are available, hence the hypothesis that the amount of harmful substances stored in tubers depends not only on the time of their exposure to light, but also on whether they were washed or not. Methods: In order to verify the hypothesis, laboratory tests were carried out on the tubers of five potato varieties originating from a univariate field experiment. The aim of the study was to analyse the change in the content of total glycoalkaloids (TGA) and nitrates (V) in tubers of five potato varieties depending on the time of light exposition (0, 7, 14 days) and pretreatment of tubers. Results: It has been demonstrated that the content of glycoalkaloids and nitrates in potato tubers depended significantly on the variety, time of exposure to light and pretreatment. Most glycoalkaloids were accumulated in the tubers of the Lord (89.67 mg·kg−1) and Irga (89.05 mg·kg−1) varieties. The time of light exposure significantly influenced the increase in glycoalkaloids and nitrates in the studied potato tubers. The increase in TGA after 14 days ranged from 20.67 mg∙kg−1 for variety Vinieta to 54.67 mg∙kg−1 for variety Irga. The increase in nitrates ranged from 11.67 mg∙kg−1 for variety Bellarosa to 27.50 mg∙kg−1 for variety Irga. Exposure time affected the content of glycoalkaloids in a parabolic manner and the content of nitrates in a linear manner.

Effect of genotype, flesh colour and environment on the glycoalkaloid content in potato tubers from integrated agriculture

The main aim of the study was evaluation of the content of -solanine, -chaconine and total glycoalkaloids (TGA) in fourteen new potato cultivars with purple and red flesh in comparison with yellow- and white-fleshed control potatoes cultivated in a friendly way in integrated agriculture. The results were obtained from three-year trials on two locations. TGA levels in tubers’ flesh ranged from 33.69 to 167.77 mg/kg fresh matter (FM), and the ratio of α-chaconin to α-solanin from 1.18 to 3.78. No TGA safety limit was exceeded for any cultivar. The glycoalkaloids content was not significantly influenced by flesh colour, whereas the cultivar genotype had a decisive influence on their content. Eight cultivars with coloured flesh yielded a more favourable lower TGA content in comparison with the yellow-fleshed control cv. Agria (86.3 mg/kg FM); on the contrary six cultivars showed higher TGA values. The highest average TGA content was found in the purple-fleshed Bora Valley cultivar (165 mg/kg FM), the lowest was found in the red-fleshed Red Emmalie cultivar (43.6 mg/kg FM), whereas the white-fleshed cv. Russet Burbank reached 67.0 mg/kg FM. The glycoalkaloid content was significantly affected by location and year weather conditions.

Assessment of Phytotoxic Potential of Potato Genotypes

In the laboratory studies on allelopathy, phytotoxicity is defined as a negative impact of plant’s extracts or natural compounds derived from plants, on germination and/or growth of the tested (acceptor) plant. Glycoalkaloids are the main biologically active compounds of the potato and are involved in potato phytotoxicity (the correlation coefficient of the length of the test plant with the concentration of total glycoalkaloids present in the leaf extracts of forty potato genotypes was r = -0.41). The assessment of phytotoxic abilities of the potato is a two-step procedure which consists of determining glycoalkaloids in potato leaf extracts and analyzing the root and hypocotyl lengths of the test plant growing in potato leaf extracts.

Effect of cultivar, flesh colour, location and year of cultivation on the glycoalkaloid content in potato tubers

In the three-year field trials (2009–2011) at two locations with different altitudes a total of 14 potato cultivars with different colour of flesh (yellow, white, red and purple) were grown. The content of total glycoalkaloids (TGA) was determined by HPLC. TGA content ranged from 18.8 to 102.4 mg/kg fresh matter and none of the cultivars reached the value of risk to human health. Conclusive and decisive influence on the content of the TGA was recorded in genotype. Individual cultivars reached 0.47 to 1.45 of the TGA content in the control cv. Agria. In terms of the colour of the flesh the highest TGA content was found in group of red-fleshed cultivars (1.53 × higher than the average of cultivars with yellow or white flesh); while red-fleshed cv. Rote Emma reached the absolutely lowest TGA content of 14 cultivars, which confirms the decisive role of genotype. On warm, dry habitats in the lowlands a higher TGA content was observed when compared with the amount raised in a typical potato field.

Influence of High Temperature and Reduced Irradiance on Glycoalkaloid Levels in Potato Leaves

Growth chamber and greenhouse experiments were conducted to investigate the effect of temperature and irradiance on foliar glycoalkaloids of three potato genotypes (Solanum tuberosum L.) that differ in glycoalkaloid content. Two genotypes (ND4382-17 and ND4382-19) produced the acetylated glycoalkaloids, leptine I and II, that contribute resistance to the Colorado potato beetle (CPB, Leptinotarsa decemlineata Say). The glycoalkaloids were separated and quantified by high performance liquid chromatography. Exposure of plants to high temperature (32/27 °C, 14-hour day/10-hour night) for 3 weeks under a 14-hour photoperiod with an irradiance of 475 μmol·m-2·s-1 significantly increased the levels of leptines I and II, solanine, and chaconine compared to that at low temperature (22/17 °C). Increases in foliar leptines and total glycoalkaloids at high temperature were 90% and 169%, respectively. Growing potato plants at low irradiance (75% reduction) for 2 or 4 weeks resulted in a significant reduction in the levels of leptine I and II (46%), solanine (43%), and chaconine (38%) compared to nonshaded plants. Transferring plants from high to low irradiance or from low to high irradiance for 2 weeks caused a decrease and an increase in glycoalkaloid concentration, respectively. Therefore, both temperature and irradiance influenced foliar levels of glycoalkaloids in potato plants without changing the leptines and solanine to chaconine ratios. Thus, irradiance and temperature influenced glycoalkaloid compounds that can effect resistance to CPB, especially leptine I and II.