2015 Spring – Research Updates

Methods for Ethylene Control: Nanotechnology

Note: In the last issue, three classical approaches to ethylene control were summarized: genetic strategies, environmental strategies, and chemical strategies. The use of nanotechnology is a relatively new, innovative approach that shows promising application in postharvest care of cut flowers.

Ethylene is a plant growth regulator involved in a variety of physiological processes including germination, growth, floral initiation and opening, senescence, abscission and fruit ripening. Responses to ethylene vary widely by plant species. Much is known about ethylene at the biochemical and genetic levels and numerous strategies have been developed to reduce ethylene production or inhibit its action to prolong flower postharvest performance.

Nanotechnology is defined as the design, characterization, production and application of structures, devises and systems by controlling the shape and size at the nanometer scale. Nanoparticles and nanoporous materials can be used to carry ethylene action inhibitors, control growth and development of microorganisms and introduce a new generation of packaging.

Postharvest Ethylene Detection and Removal

Ethylene gas sensors are used in the fruit and vegetable industry to detect and monitor the concentration of ethylene in the environment. Tin dioxide is the most common nano-material used for detection in ethylene sensors, though other metal oxides are also used. These materials are used in resistor-based devices, where their conductivity increases or decreases as an effect of the exposure to ethylene concentrations. Gas sensors containing nanostructures, such as nanowires, identify the odorant mimicking natural olfaction and estimate its concentration. This device is called an e-nose. Changes in the postharvest environment can be made in appropriate response to the information provided by the e-nose. While the application of ethylene gas sensors could be useful in the cut flower industry, particularly in storage rooms of large growers and wholesale markets, a cost-benefit analysis needs to be done to evaluate whether the gain in vase life would compensate the extra cost of monitoring and removal.

Packaging technologies are another means of maintaining a desirable atmosphere. Nano-scale fillers can be incorporated in plastic films making them more impermeable to ethylene. Nano-components might be used to create ethylene-scavenging bags or a nanoparticle-promoted absorbent matrices might be included in traditional packaging to remove ethylene. Nano-catalytic degradation where the organic contaminant is actually destroyed is also being researched. Titanium dioxide has been the focus of light-activated photocatalytic degradation, but the constant need for UV light (whether natural or artificial) is a limiting factor. Research is still in the early stages for the floriculture industry, but prototypes have demonstrated potential economic feasibility for commercial cut flower applications.

Ethylene Action Inhibition

Cyclodextrin nanosponges (CD-NSs) were initially used for removing persistent organic pollutants in water purification. They have since been adapted for use in cosmetics, medicine and agriculture. As a postharvest delivery system, CD-NSs have been successful in harnessing the gaseous 1-MCP. Not only did research indicate 1-MCP in a CD-NS prolonged vase life (by 5 days, compared to gaseous 1-MCP), it also controlled damage from Botrytis cinerea. While gaseous 1-MCP is highly unstable and reactive, in inclusion in a CD-NS appears to stabilize it and preserve its ethylene inhibition properties. While more research is required, the 1-MCP CD-NS is a promising user-friendly formulation that may be economically viable in the the cut flower industry, offering prolonged vaselife and control of fungal diseases.

Scariot, V., R. Paradiso, H. Rogers, and S. De Pascale, 2014. Ethylene control in cut flowers: Classical and innovative approaches. Postharvest Biology and Technology, 97 pp. 83-92.

Greenhouse Gladioulus Production

Researchers in Brazil evaluated irrigation needs and nitrogen fertilization on greenhouse-grown gladiolus. Using the variety ‘White Friendship’, which requires 60 to 65 days of cultivation, two bulbs per pot were planted 12 cm deep. Fertilization treatments consisted of five doses of nitrogen (0, 30, 60, 90, 120 mg/dm3), were divided and applied at 20, 31 and 40 days after planting.  Five levels of water replacement in the soil were tested (50%, 75%, 100%, 125% and 150% of the volume of field capacity water replacement). A software, Soil Water Retention Curves, was used to calculate the volume of water replacement for each treatment. Assessment of the growth and yield occurred at 46 and 76 days after planting. Other data collected included leaf count, plant height, length of stem and floral spike, number of flowers, flower diameter, number of days to bolting and number of days to flower.

Using a graph to display the relationship between plant height and water replacement levels, the level 132% resulted in a maximum plant height (94.5 cm or 37 in). A minimum water replacement level of 75% was required to achieve stem lengths within commercial standards.

The maximum number of flowers (12) was observed on the quadratic curve at 136%, with a minimum level of 100% suggested for best quality. Similarly, maximum flower diameter (8.75 cm or 3.44 in) was obtained at a water replacement level of 130%. The minimum number of days to flowering (62 days) was determined to be at a level of 134%.

As for the nitrogen part of the experiment, only the variable floral stem dry mass demonstrated a significant response among the treatment groups. Stems with no nitrogen applied had nearly 20% less dry mass compared to stems that received 120 mg/dm3 nitrogen.

de Andrade Porto, R., M. Koetz, E.M. Bonfim-Silva, A. Castilho Polizel, T.J.A. da Silva, 2014. Effect of water replacement levels and ditrogen fertilization on growth and production of gladiolus in a greenhouse. Agricultural Water Management, 131 pp. 50-56.