Articles
THE ROLE OF BACTERIA IN REDUCTION OF CUT FLOWER VASE LIFE
Microorganisms may physically block the cut flower stem (Put and Klop, 1990), produce enymes which break down walls of conducting xylem vessels (Burdett, 1970), produce ethylene or induce its production in the flower and thus accelerate deterioration (Zagory and Reid, 1986), or produce toxic metabolites (Accati-Garibaldi, 1983). We therefore investigated effects of bacteria on cut flower water relations and the nature of blockages by holding various common cut flowers in pure bacterial suspensions of known concentration
Treatment of cut chrysanthemum flower stems with Pseudomonas sp. significantly affected flower behaviour.
Mean vase life was 24.3 days compared with 29.2 days for untreated flowers, while cumulative water loss was 12.1 ml and 18.4 ml respectively.
Stem resistance to water flow in basal stem segments was significantly higher in treated flowers, and increased throughout the experiment.
It corresponded to an increase in bacterial numbers in the stem segment of both treated and untreated flowers.
Stem resistance 6 cm above the stem base was much lower than in the basal segment, but increased over time and was higher in treated flowers.
Examination of cut flower stem surfaces by ESEM showed deposits of material, thought to be bacterial extra-cellular polysaccharides (BEPS), completely covering the vascular tissue.
Previous studies relying on tissue fixation prior to SEM examination have not revealed such deposits, possibly through their loss during tissue preparation.
Similar observations were made on carnation stems, with stem resistance to water flow being greatest in the basal section of treated stems, and BEPS-like material covering the vascular tissue.
Removal of a 1 cm stem section from the base of treated carnation stems at day 15 caused a dramatic decrease in stem resistance to water flow.
The evidence is consistent with there being a blockage of xylem vessels at the cut surface by BEPS, reducing the number of functional vessels.
Increased resistance to water flow further up the stem is likely to be the result of cavitation induced by decreasing stem water potential and not by bacterial cells or BEPS, as no evidence of these was found under ESEM examination.
The increase in resistance coincided with a reduction in the number of active xylem vessels in the stem segments as measured using acid fuschin dye feeds.
Most bacteria commonly isolated from cut flower vase water are capable of producing BEPS (de Witte and van Doorn, 1988), and so blockage of xylem vessels at the cut surface of flower stems by BEPS may be a major mechanism in loss of cut flower vase life.