Photosynthetic Daily Light Integral during Propagation Influences Rooting and Growth of Cuttings and Subsequent Development of New Guinea Impatiens and Petunia

Abstract

<jats:p>A majority of commercial propagation of herbaceous ornamental cuttings occurs during the winter when the photosynthetic daily light integral (DLI) is relatively low. We quantified how the mean DLI influenced rooting and subsequent growth and development of two popular vegetatively propagated species, New Guinea impatiens (<jats:italic>Impatiens hawkeri</jats:italic> Bull.) and petunia (<jats:italic>Petunia</jats:italic> ×<jats:italic>hybrida</jats:italic> hort. Vilm.-Andr.). Three cultivars of each species were propagated under a mean DLI ranging from 1.2 to 10.7 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>. Cuttings were rooted in a controlled greenhouse environment maintained at 24 to 25 °C with overhead mist, a vapor-pressure deficit of 0.3 kPa, and a 12-h photoperiod. Rooting and growth evaluations of cuttings were made after 8 to 16 d. In a separate experiment, rooted cuttings under DLI treatments were then transplanted into 10-cm containers and grown in a common greenhouse at 21 ± 2 °C under a 16-h photoperiod to identify any residual effects on subsequent growth and development. In both species, rooting, biomass accumulation, and quality of cuttings increased and subsequent time to flower generally decreased as mean propagation DLI increased. For example, root number of petunia ‘Tiny Tunia Violet Ice’ after 16 days of propagation increased from 17 to 40 as the propagation DLI increased from 1.2 to 7.5 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>. In addition, cutting shoot height decreased from 6.3 to 4.5 cm, and root and shoot dry biomass of cuttings harvested after 16 days of propagation increased by 737% and 106%, respectively. Subsequent time to flower for ‘Tiny Tunia Violet Ice’ from the beginning of propagation decreased from 50 to 29 days as propagation DLI increased from 1.4 to 10.7 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup> regardless of the DLI provided after propagation. In New Guinea impatiens ‘Harmony White’, root and shoot dry weight of cuttings increased by 1038% and 82%, respectively, and subsequent time to flower decreased from 85 to 70 days as the propagation DLI increased from 1.2 to 10.7 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>. These experiments quantify the role of the photosynthetic DLI during propagation on the rooting and subsequent growth and development of vegetatively propagated herbaceous ornamental cuttings.</jats:p>

Supplemental But Not Photoperiodic Lighting Increased Seedling Quality and Reduced Production Time of Annual Bedding Plants

“…For example, Hutchinson et al (2012) found that TTF for vegetatively propagated angelonia (Angelonia angustifolia) 'AngelMist White Cloud' and osteospermum (Osteospermum ecklonis) 'Voltage Yellow' was related linearly to the propagation DLI, with a greater DLI leading to earlier flowering at finish. Similarly, Lopez and Runkle (2008) found that TTF decreased for cuttings of petunia 'Tiny Tunia Violet' and 'Supertunia Mini Purple' as the propagation DLI increased from 1.4 to 10.7 mol · m -2 · d -1 . Species that flower earlier when grown under greater light environments exhibit a facultative irradiance response and generally develop fewer nodes before flowering as a result (Erwin et al, 2017).…”

“…For impatiens, both HPS and LED SL during propagation decreased TTF compared with PL or natural light. Previous studies have shown that a greater propagation DLI generally decreases TTF for both seedlings and cuttings (Hutchinson et al, 2012;Lopez and Runkle, 2008;Oh et al, 2010). For example, Hutchinson et al (2012) found that TTF for vegetatively propagated angelonia (Angelonia angustifolia) 'AngelMist White Cloud' and osteospermum (Osteospermum ecklonis) 'Voltage Yellow' was related linearly to the propagation DLI, with a greater DLI leading to earlier flowering at finish.…”

A supplementary lighting and regulatory scheme using a multi-wavelength light emitting diode module for greenhouse application

“…However, the three-dimensional cultivation techniques developed by the advanced greenhouse industry are insufficient, and the light intensities provided to plants by such methods are also insufficient. 28,29 Because the lower layer of a multi-layer cultivation frame is blanked by the upper layer, the average amount of sunlight of lower layer is less than that of upper layer. In fact, plants may be grown in vain as a result of various forms of sunlight radiation loss, such as reflection loss, transmission loss, and penetration loss, which can make plants unable to achieve maximum photosynthetic effects.…”

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

“…The rate at which callus and adventitious root (AR) initials develop is temperature-dependent, thereby effecting AR formation (ARF) in cuttings. In addition, outdoor DLIs during late winter to early spring months are relatively low (5 to 20 mol · m -2 · d -1 ) compared with summer and fall months (30 to 50 mol · m -2 · d -1 ; Korczynski et al, 2002) and can be reduced by 50% or more from the greenhouse glazing material (Hanan, 1998) with further reductions from greenhouse infrastructure shading, white wash, and shade curtains (Lopez and Runkle, 2008). Although low DLIs (#5 mol · m -2 · d -1 ) during the early stages of propagation may be beneficial for minimizing stress and developing callus, excessively low DLIs (#2 mol · m -2 · d -1 ) can result in little to no ARF in cuttings.…”

“…Previous research has investigated the effects of DLI and SL from high-pressure sodium (HPS) lamps and LEDs during AR development and subsequent rhizogenesis of numerous genera of vegetatively propagated annual bedding plants Hutchinson et al, 2012;Lopez and Runkle, 2008). In controlled environments, the effects of SSL provided by LEDs during seedling (plug) propagation (Randall and Lopez, 2015;Wollaeger and Runkle, 2015) and in vitro propagation (Budiarto, 2010;Gu et al, 2012;Jao et al, 2005) have been documented.…”