Effects of light quality and quantity on flower initiation of Fragaria chiloensis L. CHI-24-1 grown under 24 h day-length

• New type of light reaction of flower initiation is exhibited.
• Visible and FR light are effective to induce flower initiation of CHI-24-1.
• Light wavelength dependence of flower initiation under 24 h DL is detected.

Flower initiation of a wild strawberry strain, Fragaria chiloensis CHI-24-1, is induced by 24 h day-length including a far-red (approximately 700–740 nm wavelength) light component. The photo-induction response differed from the response of long day plants in that no flower initiation occurred without continuous exposure to the far-red light component, even if grown under 24 h day-length. To characterize the flower initiation habit and photo-control mechanism of the CHI-24-1 plants under 24 h day-length, the effects of light wavelength and photon flux density on flower initiation were examined under various 24 h day-length treatments. As the results, flower initiation habits of the CHI-24-1 were made clear under 24 h day-length. (1) Both far-red and visible light were effective to induce flower initiation. (2) A threshold photon flux density to induce flower initiation existed in each monochromatic LED board. (3) Threshold photon flux densities differed according to the light wavelength. (4) Flower initiation occurred if the photon flux densities of the monochromatic LED board exceeded the threshold photon flux densities. These flower initiation habits of the CHI-24-1 were different from the flower initiation habits of long day plants. Additionally, the Pfr form of phytochrome seems to have sole control of flower initiation, as the action spectrum had its greatest peak at approximately 712 nm, with a smaller one in the blue region.