Abstract
Studies have successfully shown that additional far-red (FR) light can induce earlier flowering in strawberries (
Fragaria ×ananassa
). However, our understanding of the optimal plant growth phase for applying FR light remains incomplete. To optimize the appropriate time of FR light application, the June-bearing strawberry ‘Keepsake’ was irradiated at different growth phases with supplemental FR light at 43.2 µmol·m
−2
·s
−1
at a peak wavelength of 730 nm. The treatments were FR light applied from transplanting to harvest (FR++); FR light applied for the first 40 days after transplanting (FR+−); FR light applied from 40 days after transplanting to harvest (FR−+); and natural light only (FR− −). Supplemental FR light (FR++ and FR+−) elongated the petiole and caused a steep leaf angle, resulting in an extended canopy height. While the dry biomass of the plants remained unaffected, the plants receiving FR light during the initial growth phase (FR++ and FR+−) showed a reduction in leaf area compared with those receiving natural light only or FR light 40 days after transplanting. Far-red light caused early flowering and earlier fruit output; however, this benefit was outweighed by reduced fruit diameter. Plants that received FR light 40 days later produced larger fruits, and they were on par with FR− −. Far-red light timing affected nutrient concentration in plant foliage. Plants subjected to FR light in their early growth phase had lower calcium and magnesium levels while demonstrating elevated iron levels. Manganese concentration was lower in plants exposed to continuous FR light. Therefore, applying FR light during the latter growth phase under natural light conditions may be advantageous in some June-bearing strawberry cultivars.