sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

2.2. Pathogenicity testing
SDÜ Faculty of Forestry Journal
Figure 3: Cuttings with small necroses
The pathogenicity of two strains of P. syringae was analysed at cuttings of
eight different poplar clones tested at 20-21°C under greenhouse conditions. The
cuttings that were intact from outward appearance with a length for 12 – 15 cm
were harvested after a frost period in winter, and were grown with illumination
(35-60 µE m -2 s -1 ) in beakers with water for 8 days. After bud break, the cuttings
were inoculated with bacterial suspension (10 8 cfu/ml) for two days, plugged into
moist sand, and cultivated for further five weeks at 20-22°C with additional light
of 4 h (180-200 µE m -2 s -1 ) in greenhouse. The deleterious effect caused by the
bacteria was assessed by counting the cuttings with symptoms weekly. Symptoms
that were visible on young leaves and shoots had started with discoloration and
leaf spots after 3 weeks and resulted in blackening and wilting of buds and young
shoots. In general, 37.8 % and 40.9 % of the cuttings (n=88 and 87, resp.), treated
with two different P. syringae strains developed severe symptoms on young shoots
(table 1). Most of the shoots of affected cuttings died off within the observation
time of five weeks, even though the eight poplar genotypes responded to bacterial
infection quite differently. The P. maximowiczii hybrids as well as the aspen clone
were more susceptible than the other clones tested. Within the observation time,
some single control cuttings of three poplar genotypes (4 % of total) died off by
unknown causes.
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