Comparison of Sole-source and Supplemental Lighting on Callus Formation and Initial Rhizogenesis of Gaura and Salvia Cuttings

Abstract

Variability in outdoor daily temperatures and photosynthetic daily light integrals (DLIs) from early spring to late fall limits the ability of propagators to accurately control propagation environments to consistently callus, root, and yield compact herbaceous perennial rooted liners. We evaluated and compared the effects of sole-source lighting (SSL) delivered from red (R) and blue (B) light-emitting diodes (LEDs) to supplemental lighting (SL) provided by high-pressure sodium (HPS) lamps on herbaceous perennial cutting morphology, physiology, and growth during callusing and initial rhizogenesis. Cuttings of perennial sage (Salvia nemorosa L. 'Lyrical Blues') and wand flower (Gaura lindheimeri Engelm. and A. Gray 'Siskiyou Pink') were propagated in a walk-in growth chamber under multilayer SSL provided by LEDs with [R (660 nm)]: [B (460 nm)] light ratios (%) of 100:0 (R 100 :B 0 ), 75:25 (R 75 :B 25 ), 50:50 (R 50 :B 50 ), or 0:100 (R 0 :B 100 ) delivering 60 mmol · m L2 · s -1 for 16 hours (total DLI of 3.4 mol · m L2 · d L1 ). In a glass-glazed greenhouse (GH control), cuttings were propagated under ambient solar light and day-extension SL provided by HPS lamps delivering 40 mmol · m L2 · s -1 to provide a 16-hour photoperiod (total DLI of 3.3 mol · m L2 · d L1 ). At 10 days after sticking cuttings, callus diameter and rooting percentage were similar among all light-quality treatments. For instance, callus diameter, a measure of growth, of wand flower cuttings increased from an average 1.7 mm at stick (0 day) to a range of 2.7 to 2.9 mm at 10 days after sticking, regardless of lighting treatment. Relative leaf chlorophyll content was generally greater under SSL R 75 :B 25 or R 50 :B 50 than all other light-quality treatments. However, stem length of perennial sage and wand flower cuttings propagated under SSL R 50 :B 50 at 10 days were 21% and 30% shorter and resulted in 50% and 8% greater root biomass, respectively, compared with those under SL. The herbaceous perennial cuttings propagated in this study under SSL R 50 :B 50 were of similar quality or more compact compared with those under SL, indicating that callus induction and initial rooting can occur under LEDs in a multilayer SSL propagation system.

The Application Timing of a Cytokinin B-Mo-based Product Affects the Characteristics of Rooted Cuttings and Nonstructural Carbohydrates of Coleus (Plectranthus scutellarioides cv. Wild Lime) during Adventitious Root Development

“…The callus formation stage encompassed the time when the callus was visible before any visible root emergence. Callusing is the first step in protecting the wound after a cutting is harvested and is primarily composed of undifferentiated cells or a cluster of irregular proliferation at the wound site (Kennedy 2008;Owen and Lopez 2017;Vallejo et al 2018). Our visual indicator of callus formation was the tissue at the base of the wound, which tended to swell and whiten.…”

LED Lighting to Produce High-Quality Ornamental Plants

“…Adventitious rooting is a critical process in the vegetative propagation of ornamental plants, and LED lighting positively affects the growth, survival, and rooting of cuttings. Compared to the application of red or blue light alone, the combined use of red and blue light (R:B ratio of 1:1) in a multilayer sole-source light propagation system reduced stem elongation and improved root biomass in herbaceous perennial cuttings, while avoiding damage during shipping and transplanting [40]. Cuttings are susceptible to fast drying, and the control of transpiration can be achieved using a well-balanced light spectrum, since the stomatal opening response is predominantly initiated by blue light but enhanced under a strong red-light background [78,79].…”

“…The use of LED supplemental lighting enriched with red and blue wavelengths has been reported to increase the accumulation of anthocyanins and carotenoids, leading to a vivid foliage color and an overall improvement in plant's decorative value [28]. In geraniums and purple fountain grass plants, the supplementation of red and blue LED light at the end of production significantly enhanced red color saturation, expressed as the chroma index, thus increasing aesthetic appeal, quality, and market value [40].…”

The Role of Blue and Red Light in the Orchestration of Secondary Metabolites, Nutrient Transport and Plant Quality

“…Appropriate spectral qualities can positively influence the growth and survival of cuttings. Herbaceous perennial cuttings grown in a multilayer sole-source light propagation system equipped with red/blue light (R/B, 50:50) showed an increase in root biomass production and stem extension, which are valuable features for preventing damage during transport and transplantation [ 46 ]. Using blue in a strong red light background might have a positive control on transpiration, preventing the fast drying of cuttings, as blue light is responsible for stomatal opening response and effectively increases the number of trichomes that are linked to avoid the loss of water by transpiration [ 47 , 48 ].…”