Alternative inoculum sources for fire blight : the potential role of fruit mummies and non-host plants

Abstract

Fire blight is the most damaging bacterial disease in apple production worldwide. Accepted sites for the overwintering of Erwinia amylovora, subsequently providing primary inoculum for infection in the spring, are cankers and asymptomatic infected shoots. In the present work, we investigated further potential sources of inoculum. Real Time PCR assays covering a three-year-period classified 19.9 % of samples taken from fruit mummies as positive. Bacterial abundance in fruit mummies during autumn, winter and spring was up to 109 cells per gram of tissue and correlated well with later infection rates of blossoms. Blossoms of non-host plants growing close to infected trees were shown to be colonized by E. amylovora and enable epiphytic survival and propagation of bacteria. Our results indicate a potential role of fruit mummies and buds in overwintering and as primary inoculum for dissemination of the pathogen early in the growing season. Non-host blossoms may also serve as inoculum source in the built up of the pathogen population. Both aspects may contribute significantly to the epidemiology of E. amylovora. The significance of infected rootstocks as inoculum source is discussed. Fruit mummies might be used to determine pathogen pressure in an orchard before the beginning of the blooming period. This article is protected by copyright. All rights reserved.