ISHS Acta Horticulturae 704: X International Workshop on Fire Blight
INFLUENCE OF RAIN ON THE TRANSIENT POPULATIONS OF ERWINIA AMYLOVORA ON LEAF SURFACES |
| Authors: | S.C. Ockey, S.V. Thomson |
| Keywords: | apple, pear, leaf imprinting, epiphytic, dispersal |
| DOI: | 10.17660/ActaHortic.2006.704.13 |
| Abstract:
A leaf imprinting technique was used to study the epidemiology of Erwinia amylovora on leaves and ultimately improve the timing of bactericide applications for shoot blight control. Pear and apple leaves were imprinted from varying distances around active fire blight infections by placing the leaf directly onto CCT, a semi-selective and diagnostic media. Imprints made immediately before and after rain were incubated and examined for the presence of E. amylovora. The percent of leaf area occupied by E. amylovora was estimated by analyzing digital images of the bacterial colonies that grew on the imprinted plates. For all experiments in 2000, the mean percent leaf area covered with E. amylovora colonies within 0.3 m of an infection ranged from nearly zero one day before rain, 3-24% immediately after the rain and nearly zero one day following the rain. The area covered with E. amylovora on leaves imprinted from greater than 0.3 m of the infection was nearly zero before the rain and did not change significantly immediately after the rain or one day after the rain. On the day of the rain, leaves on an adjacent, non-infected tree were inoculated with ca 1x106 CFU/ml E. amylovora and inoculated leaves were imprinted during the same periods as naturally contaminated leaves. The mean percent leaf area covered by E. amylovora colonies ranged from 53-75% on the day of inoculation to 2.5-3% one day following inoculation. We conclude that E. amylovora is not present on leaves in very high numbers during dry weather and is only detected on leaves near infections in high numbers immediately after a brief rain. E. amylovora survived on leaves under the arid conditions in Utah for less than 24 hrs. | |
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