VIEW ARTICLE

Ecology and Epidemiology

The Role of the Stigma in Fire Blight Infections. S. V. Thomson, Associate professor, Department of Biology, Utah State University, Logan 84322; Phytopathology 76:476-482. Accepted for publication 15 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-476.

Erwinia amylovora occurs predominantly on the stigmas of epiphytically colonized flowers of Pyrus communis, Malus sylvestris, Pyracantha spp., Crataegus spp., and Cotoneaster spp. Rain facilitates the movement of bacteria from the stigmas to the hypanthia where infections generally occur. Bacteria survived better on the stigma than on the hypanthium and other flower parts. Small populations of bacteria declined when placed on the hypanthium, especially when the relative humidity was less than 20-30%. Bacteria survived at least 14 days on 80% of the pistil-inoculated flowers, whereas bacteria were reisolated from only 20% of the flowers inoculated on the hypanthium. Small populations of E. amylovora inoculated onto healthy stigmas multiplied to 10⁵-10⁶ per flower. Movement of these high populations of bacteria to the hypanthium resulted in infection.