Effect of light-emitting diodes on growth and morphogenesis of upland cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.) plantlets in vitro

The objective of this study was to determine the effects of different light-emitting diode (LED) light sources on the growth of upland cotton (Gossypium hirsutum L.) plantlets. Shoot bud apex cuttings of upland cotton (1.0 cm) were transplanted on Murashige and Skoog (MS) basal medium supplemented with 0.1 mg/l 6-benzyladenine (BA) and 0.5 mg/l naphthalene acetic acid (NAA) and cultured in vitro for 45 days. They were exposed to 50 μmol m⁻² s⁻¹ photosynthetic photon flux (PPF) and a 12-h photoperiod under six different lights: fluorescent lamp (CON), monochromatic blue LED (B), three blue and red LED mixtures (B:R = 3:1, 1:1, 1:3) and monochromatic red LED (R). The effects of the six light sources on growth and morphogenesis of upland cotton plantlets grown in vitro were investigated. Fresh weight, dry weight, stem length and second internode length were greatest in plantlets cultured under the B:R = 1:1 blue and red LED light, followed by blue LED light, and they were lowest in plantlets cultured under a fluorescent lamp. Chlorophyll content, leaf thickness, palisade tissue length, leaf and stomata area were highest in plantlets cultured under blue LED light. Root activity, sucrose, starch and soluble sugar contents were highest in plantlets cultured under red LED light. Our results showed that larger, healthier plantlets and a greater biomass of upland cotton were produced in the presence of red LED supplemented with a quantity of blue LED light. Blue and red LED (B:R = 1:1) was the most suitable light for the growth of upland cotton plantlets in vitro, and it may be used as alternative light source for an upland cotton culture system.