Far-red Light Photon Flux Density Modulate Fruit Production, Morphology, and Photosynthetic Efficiency in Strawberry

Far-red (FR) light plays a crucial role in the growth and development of strawberry plants ( Fragaria × ananassa ) by regulating photosynthesis, photomorphogenesis, and reproductive traits. This study looked at how four levels of far-red (FR) light (0, 30, 60, and 90 µmol·m −2 ·s −1 ; peak wavelength of 735 nm) affected the growth, reproduction, and photosynthesis of the strawberry ‘Keepsake’ in a semicontrolled greenhouse with natural daylight and cool temperatures. Higher FR photon flux densities (FR90 and FR60) significantly improved vegetative growth, including petiole elongation, leaf area expansion, and crown count. Chlorophyll fluorescence measurement revealed that increasing the FR photon flux density reduced the photosystem II (PSII) quantum yield (ΦPSII) and increased nonregulated energy dissipation (ΦNO), particularly under FR90, while nonphotochemical quenching (NPQ) remained unaffected. The net assimilation rate (NAR) peaked at FR60, whereas it declined under FR90 despite greater shoot biomass. Flowering and fruiting were significantly advanced in FR60 and FR90, while FR30 delayed flowering by 51 d and resulted in the lowest fruit count and mass. Fruit size was unchanged by treatments overall. Total soluble solids were greater in FR60 than FR0, whereas titratable acidity remained unaffected. These findings highlight that moderate FR light (60 µmol·m −2 ·s −1 ) optimizes photosynthetic efficiency and reproductive development of strawberry ‘Keepsake’ under a semicontrolled greenhouse environment.