TRANSIENT POPULATIONS OF ERWINIA AMYLOVORA ON LEAVES IN ORCHARDS AND NURSERIES

The spatial and temporal distribution of Erwinia amylovora on over 1000 leaves in a mixed apple orchard in Utah were monitored in the 1997–98 seasons.
Imprints of apparently healthy leaves from shoots within 0.3 m of shoot blight and on healthy trees were made on CCT media.
Populations of E. amylovora were detected on usually less than 25% of the leaves near infections but once on 90% of the leaves during a rainstorm.
The bacteria were detected only on two leaves from trees without infections in the two years.
The highest incidence was detected on leaves during or soon after rain storms but the populations declined rapidly during dry days.
There was no clear difference in the detection of the bacterium from the adaxial and abaxial surfaces of the leaf.
Detection of E. amylovora was similar in a New Zealand nursery consisting of 1 year-old susceptible MM106 and M793 rootstocks.
The bacteria were detected on less than 15% of the leaves adjacent to infected trees.
Leaf imprints of the same leaves before and after rain showed a clear increase in the incidence.
The pathogen was detected most often on leaves 3 to 20 from the shoot tip and only rarely on the younger leaves.
About 60% of the time the bacteria were found exclusively on the edge of the leaf.
Fire blight occurred on 67.6% of the trees within 6 weeks after detecting E. amylovora on the leaves of these trees.

VIII International Workshop on Fire Blight

S.V. Thomson, S.C. Gouk

fire blight, imprint method, spatial distribution, epidemiology

https://doi.org/10.17660/ActaHortic.1999.489.89