The nectary as the primary site of infection by Erwinia amylovora (Burr.) Winslow et al.: a mini review

Erwinia amylovora is the causative agent of fire blight, a bacterial disease existing as an unsolved problem in most countries where pome fruits like apple (Malus domestica) and pear (Pyrus communis) or ornamental plants of Rosaceae are grown. The primary site of colonization is the open flower. As for the establishment of the disease, the importance of various organs within the flowers is considerably different. The usual place for developing a large epiphytic population is the stigma. The actual infection will be attained by the external washing (rain, heavy dew) of bacteria from the stigma to the hypanthium. The bacteria penetrate through the openings of the nectary, so, the nectarthodes are the main entrance sites for them. Nectar is an excellent medium for growth of fire blight bacteria. Most often, however, the incidence of disease is significantly less than the percentage of colonized flowers. Little is known about the interrelationships of free moisture, nectar sugar concentration, ovary water potential, fine-structural characteristics of nectary versus the disease incidence and severity. The aim of this paper is to review the ecology and infection biology of Erwinia amylovora on floral surfaces and in floral tissues.