Effect of different light spectra on growth characteristics and photosynthesis yield of four ‎cultivars of coleus (Solenostemon scutellarioides L.)‎

In order to investigate the effect of different light spectra on growth and photosynthetic properties of four cultivars (‘Red’, ‘Black Dragon’, ‘Velvet Red’ and ‘Improd’) of coleus, in six growth chambers equipped with normal greenhouse light (control), 100 % blue light, 15 % blue light+85 %red light, 30 % blue light+ 70 % red light, 15 % Blue light+65 % red light+20 % white light and 30 % blue light+50 % red light+20 % white light, a factorial experiment as a completely randomized design was done. After five weeks of exposure of plants to different lights, photosynthetic biophysical parameters and plant growth characteristics were investigated. The maximum quantum yield of PSII (FV/FM) and relative maximal variable fluorescence (Fm/F0), significantly increased in combined treatments of 30 % blue+70 % red (‘Red’), control (cultivars ‘Black Dragon’and ‘Velvet Red’) and a combination of 30 % blue+50 % red+20 % white (‘Improd’ cultivar) was obtained. The specific energy fluxes per reaction center for energy absorption (ABS/RC) significantly increased in ‘Improd’ cultivar with 100 %blue light, a combination of 15% blue+65% red+20 % white and control treatments. Since PIABS can be used as an indicator of PSII life, the results of the present study indicate that the control treatments (‘Velvet Red’), 30% blue+70 % red (‘Red’), 30 % blue+50 % red+20 % white (‘Black Dragon’ and ‘Improd’) were suitable treatments to support the natural function of photosynthesis.