POSTHARVEST STUDIES ON THE CUT FLOWERS OF DAHLIA (Dahlia hybrida L.): I: EFFECTS OF PREVENTING LATEX FLOW, PULSING, AND HOLDING SOLUTIONS ON FLOWER WATER RELATIONS AND THE ANATOMICAL STRUCTURE OF THE FLOWER STEM.

Once the cut flowers of dahlia (Oahlia hybrida L.) Pam Asteraceae are cut
from the plant, a milky sap called latex fuses out of the newer stem base and plugs
the conducting vessels at the cut surface of the base of the flower stem. This
reduces water uptake; causing a rapid wilting of the flower and short vase life. A
comprehensive postharvest study on dahlia cut flowers was carried out during the two
successive seasons of 1995/1996 and 1996/1997, at the Vegel. and Flor. Dept.. Fac.
of Agric., Mansoura Univ. to evaluate the effects of three stepwise postharvest
treatments (and their combinations) on vase life and quality of cut dahlia flowers.
These treatments were: to overcome the latex problem ( untreated control, dipping in
ethanol solution, searing over a name, and dipping in boiling water), followed by short
term pulsing treatments (silver thiosulfate (STS), an antibiotic complex, and 8-
hydroxyquinoline sulfate (8-HQS)). In the final step, different components of the
flower holding solutions (sucrose. boric acid, citric acid. and cycocel (CCC» were
evaluated.
In this part (I), the effects of these treatments on water relations and
anatomical changes of the internal structure of the base of the stem of the cut flower
were evaluated.
The results revealed that placing the base (5 cm) of the stem in ethanol
(95%) was the best method to prevent latex problem leading 10 the highest water
uptake and maintenance of fresh weight of the flower at high values for a longer
period than searing or boiling treatments. Pulsing the cut flowers with 4 mM silver
thiosulfate (STS) for 10 minutes minimized bacterial growth and led to the highest
solution uptake and maintained fresh weight of the cut flower at high values. Although
citric acid (10 ppm) had the lowest pH value which led to reduced bacterial growth
and had the highest solution uptake, sucrose (1.5%) maintained the fresh weight of
the cut flower at higher values for a longer period compared with all other holding
solutions. Boric acid and Cycocel resulted in intermediate water uptake.
The anatomical study showed numerous scattered iaucuer vessels in the
cortex tissue at the outer periphery of vascular bundles and also in the pith tissue.
After five days from treatment, the untreated (centre') flowers showed the formation of
tyloses in the narrow xylem vessels. The celts of the cortex and pith tissues showed
severe plasmolysis, followed by hydrolysis or dissolution of cell components, and the
stem had macerated and fractionated vascutar tissues. Flowers received ethanol
treatment maintained their anatomical structure; wide xylem vessels without tyloses.
and the cortex and pith parenchyma celts were fully turgid and intact. tn case of
(Jowers that received searing treatment, the basal part of the stem became brown.
and cortex tissues and the xylem vessels were damaged. Flowers which received
boiling water treatment showed hydrolysis and dissolution of cell components.
degradation of secondary wall thickening in some xylem vessels, and the cortex
tissue gelatinized.