Effects of LEDs on net photosynthetic rate, growth and leaf stomata of chrysanthemum plantlets in vitro

Node cuttings of in vitro chrysanthemum (1.0cm)were transplanted on MS basal media supplemented with 30gl-1 sucrose and cultured for 35 days under six different light qualities: fluorescent (FL), blue LEDs (B), red LEDs (R), red and blue LEDs (RB), red and far-red LEDs (RFr), and blue and far-red LEDs (BFr). Net photosynthetic rate was highest under RB followed by FL and lowest under BFr and B. Fresh weight, dry weight and leaf area were also greatest under FL and RB, while decreased the most under BFr. Greatest stem length was obtained under R and RFr but the stem elongation was due to internode elongation, particularly, the third internode where elongation was almost double the first internode elongation. No difference was observed in the number of nodes among light treatments. Light quality also affected the size and number of leaf stomata. Plantlets under RB, where the growth was greatest (except stem elongation), had the smallest number (56.4mm-2)and largest leaf stomata (32.9µm×44.7µm), whereas those under BFr had the least growth, largest number (98.7mm-2)and smallest leaf stomata (24.3µm×31.7µm). In conclusion, R and RFr resulted in the highest stem elongation but also resulted in stem fragility due to excessive elongation of the third internode. Shoot growth excluding stem elongation was greatest under RB and FL. To increase stem length without stem fragility in chrysanthemum, it may be required to adjust the ratio of red light when mixed with blue or florescent.