Ethylene hormone has been known to play a crucial role in senescence of flowers. The sensitivity of this varies depending on the flower species [1]. Ethylene reduces the longevity of some flowers causing rapid wilting of petals (e.g. carnations), shedding or shattering of petals (e.g. snapdragons, delphiniums) or other changes to petal tissues, such as loss or change of colour (e.g. orchids). Ethylene (C₂H₄) is the simplest unsaturated hydrocarbon, is involved in the control of growth and developmental processes that range from germination to senescence [2]. Ethylene plays a crucial role in senescence of flowers, but ethylene sensitivity can vary depending on the cut flower species [1].

The last two reactions being catalyzed by ACC synthase and ACC oxidase [3]. SAM is also a precursor for the synthesis of the polyamine’s spermidine and spermine, which are related to young or actively growing tissues [4; 5]. Ethylene probably binds to specific receptors to form a complex that triggers ripening. Exposure of many types of flowers to the phytohormone ethylene has long been recognized as promoting petal senescence [6].

The increase in ethylene production was associated with petal wilting in flowers. ethylene is first produced in the pistil and the evolved ethylene induces auto-catalytic ethylene production from the petals causing an in rolling of petals and wilting of flowers [7]. Time course of ethylene production followed in three distinct phases, a low steady rate, an accelerated rise to the highest and a last phase of reduction [8].   Ethylene promotes the accumulation of sugars and inorganic materials in the ovary, which leads loss of fresh and dry weight of the petals. Ethylene did not affect cellular metabolism directly but rather indirectly through its effects on cellular metabolism and phospholipid loss. The high level of ethylene (more than 1000 ppm) plights during transport. Hence, the trend was developed to keep the scrubbers in the flower containers, but the scrubbers are effective only when it used in large quantities [8; 9].

Ethylene plays a vital role in extending the shelf life of the flowers, the reduction of ethylene evolution during the storage and transportation of flower is the biggest market challenge. Huge capital investment has been made by the growers for the production of flowers meant to be 100 per cent export oriented [10], by keeping this point, the research study was conducted to check the effect of chemical treatments and packaging materials on ethylene evolution of Tuberose (Polianthes tuberosa L.) flower under different storage conditions.

Materials and Methods

The tuberose (Jasminun sambac) was chosen based on their growing export demand. Throughout the study, un-opened flower buds of uniform size tuberoseflowers were procured from Vanguard Exports, Coimbatore (Private firm exporting tuberose flowers). The selection of packaging material was confirmed by conducting several trial experiments for storage studies. The selected packaging material was used at different level of thickness viz, 38.1 (150 gauge), 50.8 (200 gauge) and 76.2 (300 gauge) microns with a size of 26 X 21 cm.

Post-Harvest Chemical Treatments (quick dip method)

Prior to the packaging of tuberose flowers in LDPE packages, flowers were treated with chemicals based on extensive collection of reviews pertaining to the post-harvest handling of loose flowers [11, 12, & 13]. The post-harvest chemicals used for treatment were as mentioned in Table 1.

The uniformly sorted flowers were dipped in the chemical concentrations for 3 minutes and kept 15 minutes for surface drying [12].

Packaging Method

The passive modified atmospheric packaging was carried out in the experiment, after chemical treatments, the 25 g of fresh flowers were packed and heat sealed by retaining the atmospheric gas in the LDPE package.

Storage Conditions

The package was stored under both ambient (26- 27⁰C and 50- 70 % RH) and refrigerated (7-8⁰C and 80-85 % RH) conditions for ten days [14].  Throughout the study, temperature and relative humidity were measured using the thermometer and hygrometer.

Ethylene evolution

Ethylene released from flowers was predicted at 2 and 4 days after ambient storage; and 5 and 10 days after refrigerated storage using a hand held portable ethylene analyser. The ethylene evaluation was measured by directly injecting the sensor needle into the package via a rubber septum. The pump flow rate was maintained at 0.8 lpm for a response time of 40 seconds. For all the combinations of pre-treatments applied to measure ethylene evaluation, data were recorded and subjected to factorial completely randomized block design using AGRES statistical package.

Results and Discussion

The effect of post-harvest chemical treatments and thickness of packaging material on ethylene evolution of tuberose under ambient and refrigerated condition were evaluated. After four days of ambient storage, 50 ppm naphthalene acetic acid pre-treated flowers packed under LDPE 76.2- micron and 38.1-micron recorded minimum ethylene evolution of 27.46 ppm (Fig.2A). Among all the pre-treatments, control registered maximum ethylene evolution of 46.02 ppm at 50.8- micron packaging; the results were in accordance with [15], pre-storage pulsing treated Tuberose cut spikes had maximum shelf life when packed under HDPE packaging.  In refrigerated storage, after ten days 50 ppm naphthalene acetic acid and 2 per cent boric acid treated samples have minimum ethylene evolution (24.08 ppm) under 76.2-micron packaging.  Among all, the maximum ethylene evolution (38.21 ppm) recorded in 56.8-micron package (Fig.2B). The minimum ethylene evolution was recorded for Jasminum sambac flowers, when stored atrefrigerated condition as compare to ambient storage condition [16].

The thickness of the packaging material also played key role in holding the ethylene in package (Fig.2). These results were in accordance with few researchers [17,18] who reported that, film thickness (morphological changes) has different quantitative effect on the membrane permeability, but it is very difficult to predict the net effect. With respect to the chemical treatments, naphthalene acetic acid treated sample had minimum ethylene evolution under both ambient and refrigerated conditions (Fig.2A&B). The similar findings were also reported by researcher [19]. The tuberose flowers were sensitive to ethylene and produced moderate ethylene during opening and the results were in agreement with past research work [20]. The effect chemical treatment, thickness of packaging materials and their interactions were significant at1 per cent level (Table 2 &3).

Conclusion:

The post-harvest chemical treatments, thickness of packaging film had significant effect on ethylene evolution of tuberose flower. Amongst the treatments, naphthalene acetic acid and packaging (76.2-micron) material performed best in minimising the ethylene evolution both in ambient and refrigerated storage conditions.

Acknowledgments:

The author is very grateful for the contributions made by all co-authors.

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References

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