Main Article Content
Bolting and premature flowering of lettuce plants are undesirable phenomena that can render production of unmarketable plants. This study was conducted to evaluate the effect of paclobutrazol, a plant growth retardant, on lettuce. Paclobutrazol was applied as a foliar spray (0, 50, 100, 200, 400, 600 mg.L-1) and as a soil drench (500, 1000 mg.L-1) on lettuce cv. Balady after 30 days of transplanting during 2013-14 and 2014-15 seasons. The results indicated that the paclobutrazol significantly suppressed vegetative growth and consequently reduced yield. Moreover, the application of paclobutrazol during vegetative phase either as a foliar or drench application affects the propensity of plants to bolt. Foliar spray with 200 mg.L-1 retarded flower initiation and bolting about 14 days with minimal effect on vegetative growth and yield characters. The paclobutrazol treatments showed an increase in total soluble solids and dry matter content. The foliar spray treatments showed a low inhibitory effect than soil drench treatments. Besides, the foliar spray at low concentrations (50 - 100 mg.L-1) exhibited the less inhibitory effect for vegetative and yield characteristics, whereas the high concentrations (400 - 600 mg.L-1) resulted in a sharp reduction. Generally, the foliar spray exhibited acceptable results than soil drench method. It is recommended to treat plants, at vegetative phase, with 200 mg.L-1 of PBZ as a foliar spray to delay bolting about two weeks.