Potted poinsettias are one of the most important greenhouse ornamental crops in the United States, with wholesale value of $140 million in the top 15 states. The potted poinsettia was ranked number two among potted plants for its economic value and ranked number one for total amount of potted plants sold (32 million pots) (USDA, 2016).
The greenhouse production process of poinsettias could have an influence on its economic value, especially when the poinsettia production margin is low due to competitive pricing (Barnes et al., 2014). One strategy for increasing profits is to reduce production inputs, such as irrigation water, fertilizer, plant growth regulators (PGR), overhead (i.e., bench space), and labor. Applying liquid fertilizer with each irrigation is a common practice for poinsettia production (Ecke et al., 2004). Traditionally, water deficit was considered detrimental during greenhouse poinsettia production because wilting between watering decreased plant quality by causing lower leaf drop. Additionally, using water deficit as a plant height control was reported ineffective (Dole and Wilkins, 1999; Schuch et al., 1996). However, more recent studies reported that a constant 20% substrate moisture content (SMC) could be used as a replacement for PGR (daminozide) applications to produce more compact plants (Alem et al., 2015a). Plant growth regulator application may reduce bract size in poinsettia, which is detrimental to plant quality (Meijón et al., 2009).
Poinsettia is an obligate short day/long night photoperiodic plant and therefore has distinct vegetative growth and reproductive development stages during greenhouse production. The timing of application of water deficit affected poinsettia (Euphorbia pulcherrima ‘Classic Red’) stem elongation depending on growth and development stage (Alem et al., 2015a, 2015b). Periods of 20% SMC application were used for height control when plant height exceeded the target height using graphical tracking. Applied water deficit during the vegetative growth stage of poinsettia reduced transpiration rate (E) and net photosynthetic rate (Pn), but not during the flowering and bract coloring development stage (Nowak, 2002).
Grower profits are increased when overhead and labor costs and postharvest shrinkage are reduced. Poinsettia postproduction disorders include stem breakage, bract fading, leaf yellowing, bract edge burn (BEB, also known as bract necrosis), and bract bruising (Ranch, 2012). Frequent irrigation with fertilization throughout the production cycle increased botrytis infection, weak lateral stems, and late stretch, resulting in postproduction stem breakage and BEB (Barrett et al., 1995; Ecke et al., 2004; Islam and Joyce, 2015; Nell and Barrett, 1986). Postproduction environment temperature, humidity, and irregular irrigation were believed to cause leaf yellowing and leaf drop (Islam and Joyce, 2015). Meanwhile, despite the nearly four decades of research, the effect of production water usage on poinsettia postproduction longevity was still unclear (Islam and Joyce, 2015; Nell et al., 1995).
The objectives of the current study were to a) ascertain the effects of lowering SMC to conserve water during production on plant quality; b) determine if plants produced at lower SMC will acclimate to suboptimum irrigation conditions during shelf life; c) analyze the economic dimensions of traditional well-irrigated vs. water-conserving alternative irrigation methods considering production inputs and reduction in shrinkage through the market channels; and d) quantify plant quality during shelf life in a simulated retail environment.
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