Teresa Cerny

Height Control of Vegetable Seedlings by Greenhouse Light Manipulation

ABSTRACT The response of bell pepper and watermelon transplants to rigid photoselective plastic panels with four concentrations of a far red (FR) light absorbing dye was tested to develop greenhouse light manipulation as a non-chemical alternative for height control. Far red light interception increased, and transmission of photosynthetic photon flux (PPF) decreased as dye concentration increased. Light transmitted through photoselective panels reduced height of bell pepper and watermelon seedlings by ≈ 30%. The shoot dry weight of plants was also reduced with increasing dye concentration. Rigid panels with a higher dye concentration were slightly more effective in reducing plant height but the reduction in PPF with increasing dye concentration can adversely affect plant growth and development. Based on initial results, photoselective, polyethylene films were produced with a dye concentration that resulted in 75% light transmission (phytochrome photoequilibrium of 0.80) for further testing. The response of cucumber, tomato, and bell pepper seedlings was evaluated under photoselective films with two different types of dyes that reduced light transmission by 75%. Cucumber seedlings were more responsive to filtered light than tomato or pepper seedlings. Developmental rate, measured as the rate of node production, was not affected. Photoselective films reduced total shoot dry matter of cucumber and bell pepper. Smaller plants as opposed to a reduction in dry matter production primarily caused the shoot dry weight reduction under the photoselective filters. Significant reduction in stem elongation can be achieved by exclusion of FR light at the end of the day by covering west and south facing walls of the chambers or by exposing plants to photoselective films at the end of the day. However, continuous exposure of the plants to the photoselective films was most effective in reducing stem elongation.