Light Spectrum, Intensity, and Photoperiod Are Key for Production as Well as Speed Breeding of Spring Wheat in Indoor Farming.

Wheat ( L.) is the 3rd largest food crop worldwide. Growing wheat in indoor farming is a possible option for increasing future production and to facilitate speed breeding. Light is one of the most important environmental factors, but the light recipe for growing wheat in indoor farming is not well researched. We aimed to investigate the effects of light spectrum (including color temperature), intensity, photoperiod, and pattern on spring wheat growth, flowering time, and yield. Under full-spectrum white LEDs, a color temperature of 3500 K caused anthesis to be 4 days earlier and increased yield by 13% compared with 4500 K at a light intensity of 500 μmol m s. At a light intensity of 700 μmol m s, plants entered anthesis 3-10 days earlier compared to those under 300-500 μmol m s, and achieved the highest yield. Continuous light caused 3-4 days earlier anthesis but caused a 13% yield reduction compared to a photoperiod of 22 h at the same daily light integral (40 mol m day). Under a dynamic light intensity pattern (300 μmol m s from emerging to tillering; ~700 μmol m s from elongation to heading; ~400 μmol m s after flowering), flowering was triggered as early as under constant 700 μmol m s while saving ~30% of light input. We suggest that both a constant and a dynamic lighting recipe can be used to grow spring wheat indoors, potentially leading to more than seven generations per year.