2010 Spring – Research Update

A Non-volatile 1-MCP Alternative

Ethylene has a detrimental effect on the vase life of many cut flowers. It can result in undesirable abscission, senescence, physiological disorders, loss of cell turgor and pigment degradation. In the early 1990s, 1-methylcyclopropene (1-MCP) was shown to be an effective and environmentally safe ethylene blocker. The volatile character of 1-MCP limits its application to enclosed areas. Research is ongoing to evaluate 1-MCP alternatives that can be used in outdoor or open space. One promising compound is N,N-dipropyl(1-cyclopropenylmethyl) amine, or DPCA. This research evaluated the effect of DPCA on four ornamental crops: rose, carnation, geranium and orchid.

Each plant species was tested using three treatments. A preliminary experiment indicated that DPCA was more effective as a spray than as a vase water additive, so spray application was the method of choice. DPCA was sprayed to run off using five different rates: 0.4, 2, 4, 20 and 40 nmol. In the 1-MCP treatment, plants were placed in a gas-tight cabinet and exposed to 0.2 ìLL-1 1-MCP for 6 hours. For the control, plant material was placed in tap water. Evaluation of postharvest performance was based on recording visual senescence symptoms.

Both DPCA and 1-MCP significantly increased the number of days to reach each stage of floret senescence in each species tested. DPCA enhanced vase life of florets in all four species, reduced ethylene production in carnation flowers and prevented chlorophyll degradation in geranium leaves. Effective concentrations of DPCA varied among the plant species tested. The researchers hypothesize that this indicates differences in penetration ability of different plant tissue (petals vs. leaves). As is the case for 1-MCP, species-specific ethylene sensitivity may also affect optimal application concentration.

While more research is needed, the potential for this new compound, DPCA, as an alternative for 1-MCP would allow easier, faster, open-air field treatment with no need for an air-tight environment.

Seglie, L, E.C. Sisler, H. Mibus, M. Serek, 2010. “Use of a non-volatile 1-MCP formulation, N,N-dipropyl(1-cyclopropenyl-methyl) amine, for improvement of postharvest quality of ornamental crops.” Postharvest Biology and Technology. 56, pp. 117-122.


Postharvest Treatment Improves Opening and Vase Life of Iris Flowers

The failure of iris flowers to open fully after dry transport and storage can be a major postharvest problem. Incomplete opening is a result of insufficient growth of the tissues that force the bud free of the constraining sheath leaves. This research, conducted at the University of California, Davis, tested a pulse treatment with the non-metabolizable Thidiazuron (TDZ), evaluating the opening and longevity of cut iris flowers. 

Iris x hollandica ‘Discovery’ flowers were harvested at commercial maturity with 0.5 cm of the tepal tips emerged from the sheath leaves. To assess TDZ concentrations, stems were pulse treated for 24 hours at TDZ rates of 0, 0.1, 0.2, 0.5 or 1 mM in deionized water. To assess TDZ treatment time, stems were placed in a solution of 0.5 mM TDZ for 0, 1, 3, 6, 12 and 24 hours. Additional treatment evaluations included flower development stage, TDZ efficacy when combined with other postharvest treatments (i.e., GA3 and sucrose) and TDZ effects on flower respiration and ethylene production.

A pulse treatment of 0.2 to 1 mM TDZ for 6 to 24 hours at 0C or 20C was shown to provide a simple and practical postharvest treatment for iris flowers to extend longevity and prevent leaf yellowing. However the research found a different TDZ concentration threshold for inhibition of leaf and floral senescence. This indicates the need for more research of TDZ concentrations on other flower species.

Other treatments suggests 20 percent sucrose in the TDZ plus GA3 pulse solution further extended flower life (6.4 days) and opening, particularly after dry storage. The efficacy of this treat-ment, even after 14 days of dry storage may provide additional marketing opportunities for shipment or special holidays, such as Mother’s Day.

Furthermore, TDZ pulsing increased the number of ‘Discovery’ iris stems that developed a second open flower as the first flower was beginning to senesce. This further increased the display life of the stems.

Macnish, A.J., C. Jiang, M.S. Reid, 2010. “Treatment with thidiazuron improves opening and vase life of iris flowers.” Postharvest Biology and Technology. 56, pp. 77-84.

UV-C Irradiation for Postharvest Treatment of Freesia

Low doses of ultraviolet light (UV) have been shown to reduce storage rots in fruits and vegetables. This is thought to be due to a germicidal effect of the UV-C on the pathogen and/or an induced defense response by the host. Since Botrytis cinerea infection is a concern among Freesia cut flower growers, particularly when shipping, this study evaluated the effect of UV-C irradiation on cut Freesia blooms. In addition to observing the specking caused by B. cinerea, postharvest quality was also assessed.

Inflorescences of Freesia x hybrid var ‘Cote d’ Azur’ were harvested at full maturity with all buds still closed. They were irradiated 24 hours after harvest at five UV-C doses: 0, 0.5, 1, 2.5 and 5 kJ m-2. Exposure times ranged from 0 to 13 minutes. Samples were artificially inoculated with B. cinerea either before or after the UV-C exposure. Evaluation of disease control was measured using a disease severity score, a count of lesion number and a measure of lesion diameter. Postharvest quality was assessed using vase life, fresh weights and wilt scores. The inflorescences that were irradiated after inoculation displayed significant disease reduction compared to those irradiated prior to inoculation. UV-C treatment after inoculation reduced the disease severity score by as much as 74 percent and reduced lesion number by as much as 68 percent (both at the 2.5 kJ m-2 dose). This implies a direct germicidal effect of UV-C on B. cinerea.

Vase life of inflorescences treated with doses of 0.5, 1, and 2.5 kJ m-2 UV-C were about the same as the control. However, exposure at 2.5 and 5 kJ m-2 UV-C did cause some symptoms of phytotoxicity, namely petal discoloration after three days.

The research concluded that UV-C may be used as part of an integrated postharvest disease management program for freesia.

Darras, A.I., D.C. Joyce, L.A. Terry, 2010. “Postharvest UV-C irradiation on cut Freesia hybrid L. inflorescences suppresses petal specking caused by Botrytis cinerea.” Postharvest Biology and Technology. 55, pp. 186-188.