Selection of biocides for use in floral preservatives

The effects of concentrations of various biocides, in a solution containing 0.2 g l −1 citric acid and 10 g l −1 glucose, were tested on cut roses ( Rosa hybrida L., ‘Classy’), Alstroemeria pelegrina L. and carnations ( Dianthus caryophyllus L.). Compounds were evaluated for their effects on flower life (time to decline in fresh weight), maximum gain in fresh weight, solution uptake from 4 to 6 days, resistance to water flow in the stem, stem respiration and solution absorbance. Longer flower life and higher gain in fresh weight of roses were observed with a concentration of 0.05 g l −1 than with higher concentrations of most biocides. At this concentration, bromopropanediol, Dantogard and thiabendazole did not prevent a rise in stem resistance to water flow, or solution absorbance. Aluminium sulphate up to 0.8 g l −1 was also ineffective in these respects. Stem respiration was inhibited by sodium benzoate, hydroxyquinoline citrate (HQC), Isocil and Physan-20. Principal component analysis on the rose data indicated that the best treatments were 0.05 g l −1 benzoate, cetylpyridinium chloride, Isocil and Physan-20, 0.05 and 0.2 g l −1 dichloroisocyanuric acid, and 0.2 and 0.8 g l −1 HQC. Tests with carnation and Alstroemeria indicated that HQC, Isocil and Physan most consistently promoted fresh weight increase and maintenance.