ISHS Acta Horticulturae 217: IV International Workshop on Fire Blight
OCCURRENCE OF ERWINIA AMYLOVORA ON APPLE FRUIT IN NEW ZEALAND |
| Authors: | C.N. Hale, E.M. McRae, S.V. Thomson |
| Abstract:
Apple orchards with different levels of fire blight infection were surveyed through the 1984–85 growing season for the presence of Erwinia amylovora on the surface of shoots, flowers and fruits at different stages in development up to full maturity. E. amylovora was not detected in washings from samples from orchards in which no fire blight symptoms were seen. The pathogen was occasionally detected in washings from shoots and immature fruit from orchards with 1–2 infections/tree. In an orchard with 75 infections/tree E. amylovora was detected regularly from shoots, flowers, immature and mature fruit. However, in this orchard the frequency of detection of the pathogen in washings from maturing fruit declined from 50% of fruit sampled for fruitlets, to 3% for mature fruits. Commercially packed apple fruit from orchards with different levels of fire blight infection were also surveyed for the presence of E. amylovora. The pathogen was not detected in washings from fruit from the orchards in which no fire blight symptoms were seen nor from fruit from the orchards with 1–2 infections/tree. However, E. amylovora was isolated from a small number (<1%) of fruit from the orchard severely affected by the disease. For both fully mature and packed fruit E. amylovora was detected in washings only from the calyx end and not from the fruit epidermis. This suggests that the pathogen is more likely to survive in association with the dried remnants of the flower parts. From the results of these surveys we conclude that apple fruit harvested from orchards in which no fire blight symptoms are seen during the growing season are unlikely to constitute a means of disseminating fire blight. | |
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