Effect of light quality with different red/far-red photon flux density ratio on elongation of pak-choi seedlings grown under high temperatures

The effect of red(R) to far-red(FR) photon flux density ratio in transparent light on the growth of pak-choi under high temperature was examined to test if stem elongation of seedlings can be controlled. Experiments were conducted under three light conditions using films with differing R/FR ratios; transparent film and films with low transparency for red and far-red light (reduced red light and reduced far-red light, respectively). The R/FR ratio (600-700 nm/700-800 nm) was 1.05 in the transparent film, 0.67 in the reduced red light film, and 1.66 in the reduced far-red light film. Stem lengths of pak-choi seedlings exposed to 29 degrees /25 degreesC (day/night) were significantly shorter under reduced far-red light and significantly longer under reduced red light than those grown under transparent film. Leaf width did not differ between the transparent film and reduced far-red light but that under reduced red light was significantly narrower. Our results indicate that stem lengths of pak-choi seedlings can be controlled, even under high temperature. conditions, by using covering them with material which increase the R/FR ratio under natural light.