Light plays a crucial role in regulating various aspects of plant growth, development, and metabolism. The absorption spectra of photosynthetic pigments are primarily concentrated in the blue (400-500nm) and red (600-750nm) regions of light, making these wavelengths particularly influential in plant morphogenesis and photosynthesis. Varying the ratios of blue to red light can produce distinct morphological and physiological outcomes in plants. Blue light enhances photosynthetic activity and promotes more compact and robust growth, while red light encourages rapid growth and flowering. These specific combinations can be optimized for desirable traits in ornamental plants. This research aims to evaluate the effects of different combinations of blue and red light on the physiological and morphological characteristics of marigold (Tagetes erecta) ‘Crackerjack’. Seeds were sowed in Metromix 820 potting mix and placed on a misting bench for germination. After germination, seedlings were subjected to three different light spectra: 10% blue and 90% red LEDs (10¬B90R), 25%blue and 75% red LEDs (25B75R), and 50% blue and 50% red LEDs (50B50R) maintained using a spectrometer (StellarNet Inc.). A 90% shade cloth was used in each treatment to prevent the effect of outside light. The photosynthetic photon flux density (PPFD) was maintained at 150 µmol.m-2.s-1 and the photoperiod was maintained at 12 h light and 12 h dark. After four weeks, various physiological and morphological parameters were assessed in five destructively harvested seedlings per treatment. We found that seedlings grown under the 25B75R treatment exhibited greater height in comparison to those under the 50B50R spectrum but similar to seedlings under 10¬B90R. Stomatal conductance (gs) and photochemical efficiency (Fv/Fm) were higher under 50B50R than in 25B75R but comparable to those in 10¬B90R. Additionally, the SPAD and NDVI values, which indicate chlorophyll content and overall plant health, were highest under the 50B50R treatment. However, leaf area, total fresh weight, and total dry weight showed no significant differences among the treatments.
