Floriculture crops represent a $4.2 billion industry in the United States with bedding plants accounting for ≈44% of their total wholesale value (USDA, 2009). In the last 17 years, there has been a change in the retailing of floriculture crops as customers purchase more bedding and garden plants from big-box retailers (mass merchandisers and club centers) and general retailers (department stores and supermarkets) and less from traditional garden centers and florists (Yue and Behe, 2008). Subsequently, the shipping and retailing of these plants may occur farther from the site of production, making proper postproduction care and handling increasingly important to ensure that customers receive the best quality plants (Starman et al., 2007). During shipping and retailing, plants may be exposed to harsh environmental conditions, including high temperatures and irregular irrigation, which cause rapid substrate drying and plant wilting. These drought-stressed plants quickly become undesirable to the customer. It is estimated that 5% of the plant material retailing at independent garden centers may become unsalable, whereas postproduction losses at the big-box retailers may be as high as 10% to 15% (Healy, 2009).
Very little research has been conducted on the postproduction care and handling of floriculture crops. Although environmental conditions during greenhouse production are optimized for plant growth and development, postproduction environments are often less than ideal. Floriculture crops suffer stress from high temperature, low light, nutrient deficiencies, and water deprivation during shipping and retailing (Armitage, 1993; Starman et al., 2007). Toning by reducing fertility and available water during the last 2 weeks of greenhouse production has been promoted as a means of “hardening off” plants so that they are less susceptible to the environmental stresses experienced after production (Armitage, 1993; Starman et al., 2007). Reduced end-of-production fertilization effectively increases the quality and shelf life of a number of containerized vegetative annuals (Beach et al., 2009). Although this production practice enhances the value of many floriculture crops under standard shipping and retailing conditions, there is no experimental evidence to indicate whether this shelf life extension would be observed if plants experienced severe drought stress.
Plant wilting can be caused by a combination of enhanced water loss and inadequate watering, and it is a major cause of postproduction decline in greenhouse crops (Barrett and Campbell, 2006). The plant hormone abscisic acid (ABA) plays a role in plant responses to environmental stresses, and ABA applications decrease water loss and enhance drought tolerance (Leskovar and Cantliffe, 1992; Yamazaki et al., 1995). The use of chemicals to reduce water loss in floriculture crops has shown variable results, but new formulations of ABA are now available for commercial growers to use as a plant growth regulator (Barrett and Campbell, 2006).
Recent research has focused on the use of concentrated ABA or ABA analogs as a means of maintaining the marketability of horticulture crops by reducing drought stress symptoms (Blanchard et al., 2007; Kim and van Iersel, 2008; Monteiro et al., 2001; Sharma et al., 2006). ABA analogs have been used to effectively reduce water use and extend the shelf life of tomato (Solanum lycopersicon), snapdragon (Antirrhinum majus), and nasturtium (Tropelaum majus) transplants (Sharma et al., 2006). The application of exogenous ABA during spring/summer production periods also reduces respiration and water loss in potted miniature rose (Rose hybrida L.) and results in increased flower longevity (Monteiro et al., 2001). Experiments with a new ABA formulation (s-ABA; ConTego™; Valent BioSciences Corp.) have shown that sprench (spray to runoff) applications of 125 or 250 mg·L−1 delay drought-induced wilting symptoms in seven of nine species of bedding plants that were evaluated (Blanchard et al., 2007). Shelf life extensions for the seven species varied from 1.1 to 5.8 d (Blanchard et al., 2007). Overall, exogenous ABA applications have the potential to enhance drought tolerance in plants, but many questions remain about the optimal application methods and effectiveness across different plant species.
The goal of this research was to investigate the effectiveness and use of s-ABA for reducing postproduction decline resulting from water stress. The specific research objectives were 1) to determine whether the application of s-ABA could effectively reduce drought-induced wilting in a variety of bedding plants; 2) to determine if the method of application influences effectiveness; and 3) to document and quantify any side effects that result from exogenous applications of ABA.
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