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 pot ato genotypes (Solanum tuberosum L,) that differ in glycoalkaloid content. Two genotypes (ND4382-17 and ND4382-19) produced the acetylated glycoalkalo ids, leptine I and II, that contribute resistance to the Colorado potato be etle (CPB, Leptinotarsa decemilineata Say). The glycoalkaloids were separat ed and quantified by high performance liquid chromatography. Exposure of pl ants to high temperature (32/27 degrees C, 14-hour day/10-hour night) for 3 weeks under a Ii-hour photoperiod with an irradiance of 475 mu mol.m(-2).s (-1) significantly increased the levels of leptines I and II solanine, and chaconine compared to that at low temperature (22/17 degrees C), Increases in foliar leptines and total glycoalkaloids at high temperature were 90% an d 169%, respectively. Growing potato plants at low irradiance (75% reductio n) for 2 or 4 weeks resulted in a significant reduction in the levels of le ptine I and II (46%), solanine (43%), and chaconine (38%) compared to nonsh aded plants. Transferring plants from high to low irradiance or from low to high irradiance for 2 weeks caused a decrease and an increase in glycoalka loid concentration, respectively. Therefore, both temperature and irradianc e influenced foliar levels of glycoalkaloids in potato plants without chang ing the leptines and solanine to chaconine ratios. Thus, irradiance and tem perature influenced glycoalkaloid compounds that can effect resistance to C PB, especially leptine I and II.