Effects of varying light quality from single-peak blue and red light-emitting diodes during nursery period on flowering, photosynthesis, growth, and fruit yield of everbearing strawberry.

We studied the effects of varying light quality on the flowering, photosynthetic rate and fruit yield of everbearing strawberry plants (Fragaria×ananassa Duch. 'HS138'), which are long-day plants, to increase the efficiency of fruit production in plant factories. The plants were grown under continuous lighting using three types of blue and red LEDs (blue light peak wavelength: 405, 450, and 470 nm; red light peak wavelength: 630, 660, and 685 nm) during the nursery period. All blue light from the various peak LED types promoted more flowering compared with red light (630 and 660 nm except for 685 nm). The longer wavelength among the red light range positively correlated with earlier flowering, whereas the number of days to anthesis did not significantly differ among blue LED treatment wavelengths, irrespective of peak wavelength. The result of a similar experiment using the perpetual flowering Fragaria vesca accession Hawaii-4 representing a model strawberry species showed almost the same pattern of flowering response to light quality. These results suggest that long-day strawberry plants show similar flowering response to light quality. The photosynthetic rate under red light (660 nm) was higher than that under blue light (450 nm). However, the plants grown under red light showed lower photosynthetic capacity than those grown under blue light. Although the light color used to grow the seedlings showed no difference in the daily fruit production, blue light irradiation during the nursery period hastened harvesting because of the advance in flowering.

The FT-like gene PehFT in petunia responds to photoperiod and light quality but is not the main gene promoting light quality-associated flowering.

In Arabidopsis, flowering is delayed under red light and induced under far red light and blue light. Studies suggest that the florigen, FLOWERING LOCUS T, is involved in the control of light quality-associated flowering in Arabidopsis. In petunia, similar to Arabidopsis, flowering is delayed under red light and induced under blue light, however its mechanism still remains unknown. Here we isolated a gene which has 75% amino acid sequence similarity with Arabidopsis FT (AtFT), named PehFT. By overexpressing PehFT in Arbidopsis and petunia, we tested its ability to induce flowering. Also, by conducting expression analyses of PehFT under different light quality treatments, we tested its response to light quality. We concluded that PehFT, like AtFT, is a gene which responds to photoperiod and light quality, but unlike AtFT, is not the main gene controlling the light quality-associated flowering.