Embolism in rose stems as a result of vascular occlusion by bacteria

Using detection of ultrasonic acoustic emissions (UAE), we tested the hypothesis that xylem blockage by bacteria in rose stems (Rosa hybrida L.) can induce cavitation. In both Madelon and Cara Mia roses, cavitation started when the bacterial count in vase water reached 108 ml-1, although the number of cavitations was higher in Cara Mia stems. Following placement in water containing 108 colony forming units (cfu) of bacteria, cavitation occurred immediately, both in Madelon and Cara Mia roses. After removal of the conduits that were opened at harvest (by recutting 25 cm of the stem end under water), prior to placement in the bacterial suspension, no cavitations were observed in stems of Madelon roses. This indicated that cavitation started with the air in xylem conduits that were opened by cutting. In contrast, recutting 25 cm under water from the stems of Cara Mia roses did not reduce the number of cavitations. It is concluded that a bacterial occlusion resulted in a high rate of cavitation, hence in a considerable number of conduits, with air bubbles. These bubbles may further impede water uptak