Improving Winter Growth in the Citrus Nursery with LED and HPS Supplemental Lighting

Authors: Bowman, Kim; ALBRECHT, UTE - University Of Florida

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2020
Publication Date: 11/23/2020
Citation: Bowman, K.D., Albrecht, U. 2020. Improving Winter Growth in the Citrus Nursery with LED and HPS Supplemental Lighting. HortScience. 56(1):21-27. https://doi.org/10.21273/HORTSCI15302-20.
DOI: https://doi.org/10.21273/HORTSCI15302-20

Interpretive Summary: Propagation of citrus trees relies upon greenhouse nurseries to protect from insects and disease, while producing good-sized grafted trees with strong root systems and leaf canopies for transplanting into field sites. The cost of producing citrus nursery trees is high, and methods to improve the success of propagation and tree growth in the nursery are of extreme importance. During the time of the year when day length is short, supplemental light was investigated as a method to improve the success and tree growth. Five experiments were conducted to evaluate the benefits of two different types of supplemental lighting on propagation of citrus trees using six of the most common rootstocks, and the three methods of rootstock propagation. Both types of supplemental light were observed to have strong favorable effects to increase plant growth with all rootstocks and propagation types. One of the light types was also observed to improve initiation of growth in the budded nursery plants. The use of supplemental light is one valuable method to improve the growth of citrus nursery trees.

Technical Abstract: Modern citrus nursery production makes use of potted-tree propagation in greenhouses. Supplemental lighting is one method by which nursery tree growth and profitability may be significantly improved, but limited specific information is available. Five replicated experiments were conducted to determine the utility and effects of increasing day length during the winter months by supplemental illumination from LED (light-emitting diode) or HPS (high-pressure sodium) lights in citrus nursery propagation. Studies used ‘Valencia’ sweet orange scion, the most common citrus fruit cultivar grown in Florida, and the commercially important rootstocks sour orange, ‘Cleopatra’ mandarin, ‘US-812’, ‘US-897’, ‘US-942’, and ‘US-1516’. Comparisons used the three common types of citrus rootstock propagation: seed, stem cuttings, and micropropagation. Six responses were measured in the lighting experiments, including vegetative growth before budding, scion bud survival, and scion bud growth after budding. Supplemental HPS or LED light to extend day length to 16 hours in the citrus nursery during short-day winter months was observed to be effective in increasing unbudded rootstock liner growth and ‘Valencia’ scion growth on all rootstocks and propagation types. Generally, the positive effect on vegetative growth from an increased day length was stronger with the HPS light than with LED light, while increasing day length with LED light, but not HPS light, provided some increased bud growth initiation. Use of HPS or LED supplemental lighting to extend day length offers significant growth advantage for the citrus winter nursery.