Pathogen-induced changes in floral scent may increase honeybee-mediated dispersal of Erwinia amylovora
Rodriguez Estrada MT
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Honeybees are well recognised for their key role in plant reproduction as pollinators. On the other hand, their activity may vector some pathogens, such as the bacterium Erwinia amylovora, the causative agent of fire blight disease in pomaceous plants. We observed a preference of foraging honeybees for healthy apple flowers over infected ones, according to three independent methods: (1) direct count of visiting bees per time frame; (2) incidence on apple flowers of a marker bacterium (Pantoea agglomerans, strain P10c) carried by foraging bees; (3) quantification of E. amylovora populations in the collected pollen loads, proportional to the number of visits to infected flowers. The characterization of volatile compounds, released by flowers revealed a different emission of several bioactive compounds, providing an explanation for honeybee preference. As an unexpected ecological consequence, the influence of infection on floral scent increasing the visit rate on healthy flowers may promote a secondary bacterial spread.