Enhancing Postharvest Performance By Ria T. Leonard and Terril A. Nell

Making flowers last longer has been the goal of the floriculture postharvest research program at the University of Florida for more than 30 years. We undertake applied research and teaching on the postharvest biology and technology of ornamentals — including cut flowers and potted flowering, foliage and bedding plants. We work in partnership with the floriculture industry to provide practical solutions to major postharvest problems.

The Program

Our research is directed at determining the impact of different production, handling, transport, storage, wholesale, retail and consumer treatments, and conditions on the postharvest performance of ornamental plants. Specific topics of interest include plant nutrition, disease, temperature, water relations, ethylene sensitivity and control, and characterizing the genotypic variation to each of these factors. We also develop and evaluate practical technologies with potential to maximize plant longevity. We have the largest floriculture postharvest facility in the country, containing more than 3,200 square feet of postharvest space where we can evaluate flowers in simulated storage, retail and consumer conditions.

We have identified key production factors, including fertilizer regimes, proper stage of marketability, transport and storage conditions, and postharvest conditions that will promote quality and flower longevity of numerous species of flowering plants. Ongoing components of our program are postharvest evaluations of new varieties of potted plants and cut flowers to identify long-lasting, stress-tolerant varieties. This information is vital for the industry to select top-performing varieties and for the continued success of commercial breeding programs. For example, we evaluate on a yearly basis potential introductions of poinsettia varieties before they are commercially introduced to ensure they can withstand the stress of transport and consumer conditions without major problems like bract edge burn, bract bruising or leaf drop. This has been invaluable information for many poinsettia breeders as they rely on our tests for selecting their breeding lines. We have also conducted intensive postharvest variety tests on the handling, storage and consumer conditions that promote quality and longevity of more than 25 species of potted bulbs (Holland Bulb Forcers Guide, Fifth Edition, 1996).

Choose the Right Variety

Of all the tests and experiments we have conducted through the years, results indicate that choosing the right variety is one of the most important and simplest ways to maximize the life of flowers. No matter the species of flowers tested, some varieties simply last longer and can withstand disease or storage conditions better than others. Of course, production and postharvest conditions play a vital role in quality and performance, but when these conditions are optimal, flower life varies considerably among varieties. Our tests show that flower longevity and plant quality can double or even triple when the right variety is selected. For example, we have found a range in pot life of 12 to 38 days for chrysanthemum, 22 to 66 days for kalanchoe, 16 to 21 days for gerbera daisy, and 14 to 38 days for hydrangea. A current test on more than 60 varieties of cut roses show vase life ranging from three to 21 days. Therefore, identifying long-lasting, high-quality varieties is a critical step to enhance postharvest performance.

Three Rules

We have found that three essential rules apply when preparing plants for shipping: First, pick the proper stage of flower development; second, use specialized pretreatments to combat common postharvest problems such as ethylene exposure and leaf yellowing; finally, make sure plants are well watered or, in the instance of cut flowers, well hydrated. Our work has shown that for some long-lasting potted plants, such as hiemalis begonia and kalanchoe, you can ship when 10 to 20 percent of the flowers are open and the remaining buds will continue to open and fully develop, yielding maximum pot life for consumers. However, for pot carnations, chrysanthemums, cyclamen or gerberas, plants need to be shipped with 25 to 50 percent open flowers, while hydrangeas need 50 to 75 percent buds open and lisianthus 75 percent buds open, or buds may not open at all.

For cut flowers, each species also has specific shipping stages that yield maximum flower opening but conserves vase life for the consumer. Many cut flowers are harvested when the buds are starting to open (rose, gladiolus), although other flower species are normally half open (chrysanthemum, carnation). Maturity of bedding plants is a vexing issue because although such plants do best if they are sold when still growing rapidly, consumers show a preference for plants with color, which are often root-bound and will not perform so well in the garden. The target is to ship plants at the stage that yields maximum quality at point of sale and ensures continued flowering and longest life for the consumer.

New Treatment Options

Specialized treatments have revolutionized how we handle the most complex and devastating postharvest problems of flowers and potted plants. Ethylene has always been an enemy of sensitive plants, accelerating senescence and causing flowers, buds or leaves to drop, wilt or discolor, and preventing buds from opening. The development of antiethylene compounds such as EthylBloc (1-MCP; 1-methylcyclopropene) or the new slow-release EthylBloc Sachet, both manufactured by Floralife and administered in gas form either before or during shipping, are effective in protecting plants from ethylene injury. Sensitive cut flowers species can also be protected from ethylene when hydrated in silver thiosulfate using commercial products such as Chrysal AVB.

Leaf yellowing, a common and distracting postharvest problem on potted and cut lilies and many cut flower species such as alstroemeria, can now be eliminated with specialized treatments or by identifying tolerant varieties. The application of gibberellins and cytokinins as dips, sprays or in solution has proved beneficial in preventing leaf yellowing in alstroemeria, narcissus, goldenrod, Oriental and Asiatic hybrid lilies, Easter lily and calla lily. Our tests have shown that leaf yellowing was dramatically reduced or eliminated in cut alstroemeria and lilies when hydrated using commercial anti-leaf yellowing products such as Chrysal BVB and PAL. The newest option for retail florists is Improved OASIS Floral Foam with Floralife Technology, which has recently been released in the market. We have seen a significant reduction in leaf yellowing of alstroemeria and chrysanthemum leaves when maintained in this foam without any prior specialized treatments.

It is well known that keeping flowers at proper temperatures during transit and storage reduces respiration rates, conserves the carbohydrate status of the flower, reduces the incidence of diseases, and increases quality and flower life. The optimum storage temperature for most nontropical flowers and plants is between 33 and 35¡ F.

Tropical blooms such as orchids, anthurium and ginger, and most potted foliage plants require holding temperatures of 50-55¡ F or higher; otherwise, severe damage or death will occur. Although temperature control is critical, it is not the cure-all for potential problems plaguing flowers.

Links to Sanitation

Our current research has focused on the role sanitation plays in flower quality. Finding new ways to combat bacteria on stem surfaces and in floral solutions has been a recent focus in our research program. Bacteria lurk on the surfaces of buckets, cutters, work benches, coolers and flower stems and can easily build up in hydration solutions without being visible. Bacteria in solutions enter and block xylem vessels, the water transport system of the stem, causing a reduction in the rate of water supply to flowers and, thus, causing premature flower death. We found that cut rose vase life decreased significantly when hydrated in a four-day-old reused hydration solution compared to a freshly made commercial hydration solution (see Figure 2 on page 30). The reused solution had a 66 percent increase in bacteria after hydrating at 40¡ F for seven days. We have recently studied the potential of a novel biocide, Selectrocide aqueous chlorine dioxide, and found it to be very effective in extending the vase life of several cut flower species by preventing the buildup of bacteria in vase solutions.

Each flower species has specific handling and care requirements needed to promote optimum postharvest performance. Treat flowers to protect against disease, water stress, ethylene exposure, leaf decline, and bacterial contamination. Maintaining proper temperatures during storage and transport is also vital in prolonging flower life and preventing diseases. Follow postharvest principles to ensure flowers will perform for the consumer. Preventing problems before they arise is the key to maximizing postharvest performance of cut flowers and potted flowering and foliage plants. It takes all segments of our industry to work together to produce high-quality, long-lasting plants for consumers.

We would like to acknowledge the supporters of our research program: AgroFresh, Inc.; American Floral Endowment; Association of Colombian Flower Exporters (Asocolflores); Center for Innovation of the Colombian Floriculture (Ceniflores); Floralife; National Foliage Foundation; Pokon & Chrysal; Produce Marketing Association; Poulsen Roser; and the many growers, importers and shipping companies that provide plant material and transportation services.

Ria T. Leonard and Terril A. Nell

Ria Leonard is a research associate and Terril A. Nell is the chair of the department of environmental horticulture at the University of Florida in Gainesville. Leonard can be reached at [email protected], and Nell can be reached at [email protected]

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