Effect of high numbers of exogenous bacteria on the water relations and longevity of cut carnation flowers

Abstract

Abstract High bacterial counts in the vase water can shorten flower longevity. The length of vase life of cut carnation flowers ( Dianthus caryophyllus L., cvs. Scania and White Sim) was reduced by placing the stems in a suspension of bacteria, when the initial exogenous concentration was 10 8 or more colony-forming units (cfu) per milliliter. The suspensions contained either the mixed bacterial population isolated from carnation stems held in water for ten days (about 50% Pseudomonas spp., 20% Acinetobacter calcoaceticus and 20% Alcaligenes sp.), or were pure culture isolates ( Acinetobacter calcoaceticus and Pseudomonas fluorescens ). The composition of the bacterial flora had no effect on longevity. The reduction in flower longevity was related to inhibition of water uptake. It is concluded that high bacterial counts in water reduce the longevity of the carnation cultivars tested. Although such high counts may not be common in vase water in consumers' homes, counts that negatively affect longevity were observed in water used for standing carnation flowers, both in specialised flower shops (in 7% of the samples) and in supermarkets (in 12% of the samples).