Bench-top Root-zone Heating Hastens Development of Petunia under a Lower Air Temperature

Abstract

<jats:p>Heating accounts for up to 30% of total operating costs for greenhouse operations in northern latitudes. Growers often lower air temperatures for production to reduce energy costs; however, this causes delays in development even in cold-tolerant crops, such as petunia (<jats:italic>Petunia ×hybrida</jats:italic>). This delay increases production time and can reduce profitability. Recent studies on low air temperature bedding plant production indicate petunia as a strong potential candidate for using lower air temperatures in combination with bench-top root-zone heating (RZH) to avoid or reduce delays in development. The objectives of this study were to 1) quantify time to flower (TTF) of seven petunia cultivars and two recombinant inbred lines (RILs) when the mean daily air temperature (MDT) was lowered by 5 °C and bench-top RZH was used and 2) determine if a high-quality petunia crop can be produced on RZH. Petunia ‘Sun Spun Burgundy’, ‘Sun Spun Lavender Star’, ‘Sanguna Patio Red’, ‘Potunia Plus Red’, ‘Potunia Plus Purple’, ‘Supertunia Red’, ‘Supertunia Bordeaux’, and two RILs, IA160 and IA349, were grown in a greenhouse with an MDT of 15 °C without RZH or with a RZH set point of 21, 24, or 27 °C. Additionally, a commercial control (CC) was established by growing plants without RZH at an MDT of 20 °C. All plants were grown under a 16-hour photoperiod to provide a daily light integral (DLI) of ≈12 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>. Time to flower was shorter at higher RZH set points. For example, TTF of ‘Potunia Plus Red’ was 56, 52, 49, or 47 days for plants grown at an MDT of 15 °C without RZH, or with RZH set points of 21, 24, or 27 °C, respectively. When a RZH set point of 27 °C was employed, TTF of all cultivars and inbred lines, except ‘Potunia Plus Red’ and ‘Sanguna Patio Red’, was similar to plants grown in the CC. Shorter stem length, lower growth index, and smaller shoot dry mass (SDM) at flowering were observed for plants grown under lower air temperatures with RZH, resulting in a more compact and high-quality plant. Producing a compact plant in a shorter time period is beneficial for growers; thus, results suggest that MDT can be lowered to 15 °C for petunia production when a RZH set point of 27 °C is employed.</jats:p>

Design and Optimization of Air Inlet in Cuttings Incubator

“…Accordingly, this study used a thermostatic plate to heat the base of the cuttings to promote rooting, providing continuous ventilation to ensure a certain temperature difference between the upper and lower parts of the cuttings. In greenhouses, studies have used electric heating wires and plates to heat the substrate [60], and many have used rubber tubes or steam pipes to provide the heat [61][62][63]. Heating wires, tubes, or pipes heat the substrate unevenly; heating plates are better, but they can transfer heat from only one side.…”

The Development of a Root-zone Environmental Control System (N.RECS) and Its Application to Flower Production

“…Olberg and Lopez (2016) suggested that when root-zone heating > 24°C was utilized during the final stage of poinsettia production, air temperatures could be reduced. Olberg and Lopez (2017) also reported that the root-zone heating of petunia by the bench top heating system can produce high-quality plants in a short period.…”