Response of Tomato and Pepper Transplants to Light Spectra Provided by Light Emitting Diodes

Abstract

Growing conditions during transplant production influence seedling quality and performance, transplant establishment, and subsequent yield. The effects of spectra combinations of blue, red, and white light, generated by monochromic light-emitting diodes (LEDs), on physiological and morphological characteristics of tomato (Solanum lycopersicum L.), cv. Kingston, and pepper (Capsicum annuum L.), cv. California Wonder, seedlings were investigated. Tomato and pepper transplants treated with monochromic red, or combinations of red with blue light, produced greater stem diameter, whereas blue light alone, or in combination with red, reduced transplant height. In tomato the most lateral branches were produced on seedlings under blue light, but pepper transplants were not affected. The most leaf area in tomato and pepper transplants was obtained under monochromatic blue or red light, respectively. Proline, an important compound related to plant stress tolerance, was produced at the highest level under blue light in both plants. For tomato, red light alone or in combination with blue or white light reduced the number of leaves required before the first cluster. This occurred in pepper transplants when higher ratios of red light (up to 100%) were applied. For both plants rates of first cluster formation and first yield were higher when combinations of blue and red lights (regardless of their ratio) were used. The most vitamin C was in fruit produced on plants developed from transplants grown under blue light. Fruit total soluble solids were also higher in tomato plants developed from blue light–treated tomato seedlings. There appear to be beneficial effects due to exposure of plants during seedling development to light spectra that extends beyond transplanting. The effects of light spectra appear to be genus or species specific. The LED technology did not differ from other technologies and has merit for production of some vegetable seedlings.