Effect of high temperature and exposure duration on stem elongation of iceberg lettuce

Lettuce is a cool season vegetable that has a tendency to bolt in long day and high temperature environments. In this study, lettuce plants were exposed to two temperature transfers to evaluate the pattern of biomass accumulation, stem elongation and bolting. Plants were reciprocally transferred between two temperatures (13 and 25°C). A negative co relation was found between the temperature and shoot growth as well as dry weight. However, stem extension was positively correlated with high temperature. Lettuce plants had 46% higher shoot fresh weights at a constant temperature of 13°C, than those grown at a constant 25°C. The positive correlation between high temperature and stem elongation was a function of the duration of exposure to high temperature. However, bolting was distinguishable from stem elongation. Overall results indicated that plants could revert back to head formation even after two weeks of high temperature-induced stem elongation. However, constant exposure to high temperature causes bolting without head formation.