| dc.description.abstract | The study was conducted to investigate the influence of chemical pre-treatments, cold storage and
water quality on the post-harvest quality of lisianthus (Eustoma grandiflorum L.) cut flowers Cv. 'Kyoto
purple'. Aluminium sulphate (recommended biocide), vertical dry-storage and deionised water (OW)
were used as references for the best post harvest treatment of lisianthus cut flowers in order to
broaden the applicability of results to the floriculture industry. Three separate experiments were set up
and laid down in a completely randomised design.
Cut flowers were held in various chemical biocides namely; 8-Hydroxyquinoline citrate (8-HOC), silver
nitrate (AgN03,), aluminium sulphate {Ab (804) 3,}, sodium hypochlorite (NaOCI) or their mixtures
making a total of 13 treatment combinations. All biocides somewhat increased the post harvest quality
of cut flowers. Vase solution containing a mixture of 8-HOC and NaOCI was the most effective biocide
amongst those tested. It increased flower vase life from 10 to 29 days and floret opening from 46 to
91%. Two of the biocides tested namely; 8-HOC and AgN03 were phytotoxic causing browning and
blackening of immersed stem sections. However, this stem discolouration neither hindered water
uptake nor reduced the vase life of cut flowers. Bacteria proliferating in vase solutions were identified
as belonging to Pseudomonas, Bacillus and Xanthamonas species. All biocides tested inhibited
bacterial growth for 2-4 days when cut flowers were held in the same vase solution. Water uptake and
flower fresh weights were markedly increased when biocides were added into vase solutions.
Increased water uptake correlated positively with the vase life and floret opening of cut flowers.
The method of cold storage at 20C as well as storage duration influenced the post harvest performance
of cut flowers. Fungal infection mainly Botrytis on cut flowers was evident on primary opened florets
soon after their removal from cold storage. Flower buds of wet-stored cut flowers opened progressively
during cold storage duration and this corresponded closely to increased fresh weights. The dry-stored
cut flowers, however, remained bud tight and had lost substantial weight at the end of cold storage.
Vase life and floret opening of cut flowers were markedly decreased by wet-storage in comparison to
the dry-stored ones. Long-term storage was even more detrimental to the post harvest quality of cut
flowers. Horizontal packaging of the cut flowers at 2°C caused geotropic bending of flower pedicels.
Cut inflorescences stored horizontally in boxes had their flower pedicels remaining bent not less than
15° throughout the display period, whereas those stored vertically in boxes had no detectable
geotropic curvature. Longer periods of horizontal packaging progressively increased geotropic
curvature of flower pedicels and this in effect reduced the overall post harvest quality of cut flowers.
The influences of water quality and pH on keeping quality of lisianthus cut flowers were studied in two
separate experiments. In the first experiment, different water sources namely; deionised water (OW),
rain, tap, lake, river, and dam waters in their natural states were used to demonstrate the effects of
water quality on post harvest performance of cut flowers. In the second experiment, the same water
types had a biocide included and their pH lowered to 3.5 and then used to hold cut flowers. Effects of
pH on cut flower longevity were evaluated at 3 pH levels namely; 3.5, 5.6 and 10.0. In the first
experiment, cut flowers held in OW were of best post harvest quality. However, the accrued benefits of
using OW in comparison to other water sources were minute and may not justify its use in commercial
post harvest handling practices of the cut flowers. By only incorporating a biocide and lowering the pH
of the waters to 3.5, the vase life, floret opening, flower fresh weights, and water uptake were
increased more than two-fold irrespective of the water type used to hold the cut flowers. There was no
significant difference in flower vase lives at the 3 pH levels studied, however, at pH 10.0, floret opening
was significantly reduced from 42 to 30%. It therefore seems that by only incorporating a biocide and
lowering the pH of vase waters, the post harvest quality of cut lisianthus is markedly improved and
there may be no need in using OW in commercial handling of this cut flower.
Key words: Eustoma grandiflorum L., post harvest, biocides, cold storage, water quality, pH, vase life,
floret opening, water uptake, fresh weights | en |
