LED lighting and exogenous cytokinin enhance budbreak and winter growth of ‘Washington’ navel orange in the nursery

Authors: DE CARVALHO, DEIVED UILIAN - University Of Florida; BISI, RAYANE BARCELOS - University Of Florida; Bowman, Kim; ALBRECHT, UTE - University Of Florida

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2025
Publication Date: 12/16/2025
Citation: De Carvalho, D., Bisi, R., Bowman, K.D., Albrecht, U. LED lighting and exogenous cytokinin enhance budbreak and winter growth of ‘Washington’ navel orange in the nursery. Frontiers in Plant Science. 16:1735154. 2025. https://doi.org/10.3389/fpls.2025.1735154.
DOI: https://doi.org/10.3389/fpls.2025.1735154

Interpretive Summary: Citrus nurseries typically are forced to reduced budding activity during winter due to limited growth from short photoperiods and low temperatures in the greenhouse. Modern light-emitting diodes (LEDs) and exogenous application of plant growth regulators may mitigate these winter challenges by extending day length and stimulating budbreak. In this paper, we report on the effects of different LED spectra and the cytokinin 6-benzylaminopurine (BA) on budbreak and growth of ‘Washington’ navel orange grafted on two rootstocks during winter. The combination of full spectrum supplemental light and Carrizo resulted in the largest rootstock diameter, scion diameter, and total leaf area, as well as a 5.7-fold increase in scion dry biomass compared to Rubidoux rootstock and no supplemental light. Application of BA further improved these responses. These findings confirm the effectiveness of tailored LED light, suitable rootstock selection, and PGR strategies in optimizing citrus nursery production and quality during the winter months when natural light is limited.

Technical Abstract: Citrus nurseries face reduced budding activity during winter due to short photoperiods and low temperatures. Modern light-emitting diodes (LEDs) and exogenous application of plant growth regulators (PGRs), such as the synthetic cytokinin 6-benzylaminopurine (BA), may mitigate these winter challenges by extending day length and stimulating budbreak. Under this context, we report in this paper the effects of different LED spectra and BA on budbreak and growth of ‘Washington’ navel orange (Citrus sinensis) grafted on two rootstocks during winter. A 4 × 2 × 2 factorial design was used, including four light levels (NoSL, no supplemental light; FSL, full supplemental light; BWSL, blue and white supplemental light; and BWSL+FSL), two rootstocks (Carrizo citrange, C. sinensis × Poncirus trifoliata; and Rubidoux trifoliate orange, P. trifoliata), and two PGR levels (NoBA and BA). Each treatment was replicated six times with 24 plants per replicate, totaling 2304 experimental plants. Light was supplemented from budding to 12 weeks after budding (wab), and different horticultural responses were assessed over time. Results showed that both FSL and BWSL+FSL significantly improved budbreak and survival (79% and 77%, respectively) compared to NoSL (62%). Application of BA further improved these responses, regardless of the rootstock. Budbreak was 1.3-fold higher on Carrizo than on Rubidoux. The FSL × Carrizo interaction resulted in the largest rootstock diameter (7.80 mm), scion diameter (4.37 mm), and total leaf area (455 cm²), as well as a 5.7-fold increase in scion dry biomass (7.87 g) compared to Rubidoux × NoSL (1.38 g). FSL enhanced shoot development, with Carrizo plants producing more nodes (12) and longer internodes (242 mm) compared to NoSL (8 nodes and 132 mm) and BWSL (10 nodes and 185 mm). The BWSL × BA interaction enhanced chlorophyll content compared to most of the other treatment combinations, whereas combinations with FSL increased the leaf surface temperature. These findings confirm the effectiveness of tailored LED light, suitable rootstock selection, and PGR strategies in optimizing citrus nursery production and quality during the winter months when natural light is limited.