The infiltration ability of micro‐organismsBacillus, Fusarium, KluyveromycesandPseudomonasspp. into xylem vessels ofGerberacv. ‘Fleur’andRosacv. ‘Sonia’cut flowers: a scanning electron microscope study

摘要

Scanning electron microscope (SEM) observations have been made of transverse and longitudinal sections of xylem vessels of cut flowers ofGerberacv. ‘Fleur’and cutRosacv. ‘Sonia’after a maximum of 24 h vase life. Vase waters used were: sterile tap water; sterile tap water plus suspensions of single pure cultures ofBacillus polymyxa, B. subtilis, Fusarium oxysporummicrospores, segments of young mycelium ofF. oxysporum, Kluyveromyces marxianus, orPseudomonas putida, up to a maximum of 106and 5×107cells/ml of vase water.The results of the SEM observations showed that only a small fraction of the microbial cells entered into the vascular system with the normal intake of vase water; most microbial cells remained attached to the submerged cut surface while a small fraction of the initially attached microbes were sometimes liberated into the surrounding vase water. The SEM figures give the impression that adhesion on to the cut stem surfaces of the bacterial cells (BacillusandPseudomonasspp.) by their capsular materials may have occurred, although the cut surface possibly acted as a filter, trapping cells because of the upward pressure of the transpiration stream into the vessels. Few attached yeast cells were found, butFusariummicroconidia formed cell clusters on the cut surface, partially blocking the xylem vessel entrance;Fusariummycelium covered the cut‐surfaces as another filter layer through which only small mycelial particles could enter the vascular system.The extent of infiltration of microbial cells into the xylem vessel system depended upon the number of microbial cells/ml of vase water (up to a certain maximal number) and on the shape and size of the individual cells and the width of the xylem vessels. The end of the vase life ofGerberaandRosaflowers was marked by an extensive water stress in the xylem vessels so that the water intake necessary for a normal flower development was insufficient and wilting ensued. The water deficit may have been enhanced by secondary biochemical and physiological interactions between the microbes and the plant tissues, which may also have affected the infiltration of micro