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ISHS Acta Horticulturae 489: VIII International Workshop on Fire Blight

INFLUENCE OF AGE OF APPLE FLOWERS ON GROWTH OF ERWINIA AMYLOVORA

Authors:   S.C. Gouk, S.V. Thomson
Keywords:   fire blight, flower physiology, stigma morphology, etiology
DOI:   10.17660/ActaHortic.1999.489.91
Abstract:
The influence of flower age on growth of Erwinia amylovora, the causal pathogen of fire blight of apples and pears was investigated under arid conditions in Utah, U.S.A. Royal Gala apple flowers of one to six days old were atomized with 5x108 CFU/ml of E. amylovora, strain Ea8865nr, marked with resistance to nalidixic acid and rifampicin. Pistils were dissected and washed separately from the remaining floral parts in sterile phosphate buffered saline, and the wash plated on King's medium B amended with the antibiotics. Flowers one to three days old supported exponential growth of E. amylovora, but the bacterial populations did not increase on flowers older than three days. While three and four-day-old flowers differed in their support of growth of E. amylovora, their stigmas were not visibly different. Stigmas were shriveled and brown only on flowers older than 6 days. Under examination using scanning electron microscopy, papillae on stigmas of four-day-old flowers were collapsed and covered in mucilage. E. amylovora populations on the flower part without the pistils were characteristically lower than pistil populations for up to three-day-old flowers. The findings that age of flowers has an impact on growth and establishment of E. amylovora agreed with our findings in New Zealand.

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