Identification of b a c t e r i a in the vase water of roses, and the effect of the isolated strains on water u p t a k e

Scientia Horticulturae, 35 (1988) 285-291 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

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Identification of B a c t e r i a in the Vase Water of Roses, and the Effect of the Isolated Strains on Water U p t a k e
YKE DE WITTE and WOUTER G. VAN DOORN

Sprenger Institute, P.O. Box 17, 6700 AA Wageningen (The Netherlands)
(Accepted for publication 23 November1987)

ABSTRACT De Witte, Y. and van Doorn, W.G., 1988. Identification of bacteria in the vase water of roses, and the effect of the isolated strains on water uptake. Scientia Hortic., 35: 285-291. The bacteria that were predominant in the vase water of 'Sonia' roses were isolated and identified. All strains belonged to the genus Pseudomonas or were Alcaligenes faecalis. The isolated strainswere grown in pure culture and then added singly to autoclaved water at 105 and 107 cfu m1-1. Water uptake of 'Sonia' roses was not affected at 105 cfu m1-1, but at 107 cfu ml -~ water uptake was inhibited from the first day onward. Eight tested bacterial strains all reduced water uptake to the same degree. The isolated bacterial strains showed no pectolytic activity. Vascular blockage by thesestrains was therefore apparently not due to pectolytic breakdown of xylem cell walls. Keywords: bacteria; cut rose flowers; vase water; water uptake. Abbreviations: cfu, colony forming units.

INTRODUCTION

The vase life of cut roses is often very short because of stem bending just below the flower. Xylem blockage is one of the main reasons for stem bending (Mayak et al., 1974). Blockage of thexylem could be due to air emboli, physiological processes or bacteria (Aarts, 1957; Durkin, 1980). When a mixed population of bacteria originating from rose stems was added to vase water, the uptake of water was inhibited only at bacterial concentrations higher than 107 cfu m1-1 (Van Doorn et al., 1986). Zagory and Reid (1986) showed that two bacterial strains isolated from carnation vase solutionsdid not reduce vase life of cut roses at a concentration of 10s cfu ml-1, but at the same concentration another strain reduced vase life by 2 days. In the present experiment the predominant bacteria from the vase water of

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286 roses were identified, and the effect of the isolated strains on water uptake of roses was determined. Inorder to assess the role of the exogenous concentrations of bacteria on the vase life of roses, the total concentration of bacteria in vase water was measured. MATERIALSAND METHODS
Bacteria. - Ten rose flowers (Rosa hybrida, cultivar 'Sonia') were placed in a bottle with tap water for 6 days at 20°C, 60% RH and 15/~mol m -2 s -1 photosynthetically active radiation at flower level. The vase waterwas stirred and 0.1-ml samples were plated (spatule method) on 2-decimal dilution series of the following media: Plate Count Agar (Oxoid, 1980); Glutamic acid-Starch-Phenolred Agar, to which penicillin and pimaricin were added (Kielwein, 1969); Tryptone Soya Broth with 12 g l-1 Oxoid Agar No. 3 and 2 mg l-1 crystal violet (Oxoid, 1980; Mossel and Tamminga, 1980); Tryptone Soya Broth with 12 g 1-~Oxoid Agar No. 3, covered by a 5-mm layer of Violet Red Bile Glucose Agar (Oxoid, 1980; Mossel and Tamminga, 1980). The four different plate types are used to select aerobic bacteria, Aeromonas and Pseudomonas species, Enterobacteriaceae plus Pseudomonas species (suppression of Gram positive bacteria), and Enterobacteriaceae, respectively (Oxoid, 1980; Kielwein, 1969; Mossel and Tamminga, 1980).The plates were incubated for 2 days at 30 ° C. The colonies were visually inspected and 39 single colonies were selected, based on colour and colony form, and replaced on Plate Count Agar until pure cultures were obtained. Colonies were obtained from all mentioned types of plates, except from the last one where virtually no growth occurred. The isolates were tested for Gram stain reaction and...