PHASIC TEMPERATURE-CHANGE PATTERNS AFFECT GROWTH AND TUBERIZATION IN POTATOES

This study determined the responses of potato (Solanum tuberosum L., c v. Norland) plants to various patterns of air temperature changes over different growth periods (phasic temperature changes). In each of two experiments under controlled environments, eight treatments of temper ature changes were carried out in two growth rooms maintained at 17 an d 22C and a constant vapor pressure deficit of 0.60 kPa and 14-hour ph otoperiod. Plants were grown for 63 days after transplanting of tissue culture plantlets in 20-liter pots containing peat-vermiculite mix. T emperature changes were imposed on days 21 and 42, which were essentia lly at the beginning of tuber initiation and tuber enlargement, respec tively, for this cultivar. Plants were moved between two temperature r ooms to obtain eight temperature change patterns: 17-17-17,17-17-22, 1 7-22-17, 22-17-17, 17-22-22,22-17-22,22-22-17, and 22-22-22C over thre e 21-day growth periods. At harvest on day 63, total plant dry weight was higher for the treatments beginning with 22C than for those beginn ing with 17C, with highest biomass obtained at 22-22-17 and 22-17-17C. Shoot dry weight increased with temperature increases from 17-17-17 t o 22-22-22C during the three growth periods. Tuber dry weight was high est with 22-17-17C, and lowest with 17-17-22 and 17-22-22C. With 22-17 -17C, both dry weights of stolons and roots were lowest. Total tuber n umber and number of small tubers (<2.5 cm) were highest with 17-17-17 and 17-17-22C, and lowest with 17-22-22 and 22-22-22C, whereas number of medium tubers (2.5-5.0 cm) was highest with 22-17-22C, and number o f large tubers (>5.0 cm) was highest with 22-17-17C. This study indica tes that tuber development of potatoes is optimized with a phasic patt ern of high temperature during early growth and low temperature during later growth.