The role of the stigma in fire blight infections.
Erwinia amylovora occurs predominantly on the stigmas of epiphytically colonized flowers of pear, apple, 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 RH was <20-30%. Bacteria survived at least 14 d 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/flower. Movement of these high populations of bacteria to the hypanthium resulted in infection.