Erwinia amylovra Infection of Hawthorn Blossom: III. The Nectary

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Abstract
The nectaries of hawthorn flowers on detached branches were inoculated with Erwinia amylovora and the population development was followed by viable counts and light and electron microscopy. On nectaries bearing surface moisture at the time of inoculation (“wet nectary” material), the population increased rapidly after a short drop, or lag, lasting 6–12 h. Scanning electron microscopy showed that bacteria had multiplied within the nectarthodes during the first 6 h after inoculation, although, the total population had dropped. Death of cells on the surface of the nectary, possibly due to desiccation, may account for the overall drop. This differential response is not consistent with a bactericidal effect of the hawthorn nectary. On nectaries lacking surface moisture at the time of inoculation (“dry nectary” material), there was a 36 h lag period before the population started to increase – which coincided with the commencement of nectar production.Although the nectary is an important site of infection during humid periods, the role of contaminated nectar in blossom‐to‐blossom spread of the disease is probably not of great importance.