Joint International Conference on Long-term Experiments ...

white light of 105 μMol s -1 m -2 using 16/8 hour light/dark cycles. The temperature was
20-22 C 0 . Three-week-old in vitro potato plants were infected during the experiments.
Pectobacterium chrysanthemi was grown at 26 C 0 on Nutrient medium. The bacterial
suspension contained 10 8 CPU. The inoculation was made by a forceps immersed in the
suspension. On control treatment we wounded the shoots with a forceps immersed in
sterile distilled water.
The symptoms were evaluated after one week. For evaluation of the data disease
rating were used. The diseased plants were divided into five categories based on the
number of the wilted leaves. The disease categories were determined as follows:
� Symptom-free plantlets
� 1-25 % of leaves wilted
� 26-50 % of leaves wilted
� 51-75 % of leaves wilted
� 76-100 % of leaves wilted
With modification of this method a special disease rate (DR) was worked out:
Σ [(N1 x 1) + (N2 x 2) + (N3 x 3) + (N4 x 4) + (N5 x 5)]
DR = --------------------------------------------------------------------------
Σ N
N1-5: Number of plantlets in each disease category
N: All obtained plantlets
RESULTS AND DISCUSSION
The results of experiments are summarized:
During the experiments we chose the virulent strains of Pectobacterium chrysanthemy.
We worked out in vitro methods of infection. We described the symptoms after in
vitro infection. Disease rate was used for evaluation of the data. With the help of
disease rate we quantified the observable differences (symptoms). We separated three
sensitivity categories:
If 1 < DR < 2 non sensitive
If 2 < DR < 3 middle sensitive
If 3 < DR very sensitive
Symptoms: The symptoms were evaluated after in vitro infection on the seventh day. In
the control treatment the plantlets were healthy. No any leaf or stem symptoms could be
observable. The place of wounding could be seen but became dry (Figure 1). In the case
of clone 34/85 were not any leaf symptoms, at the worst case below or beyond
wounding stem symptoms could be observed. The place of wounding could be seen
(Figure 2). Wilt of the one-one leaf could be observable in the Réka and Rachel. The
place of the wounding could be seen clearly. Stem symptoms were typical. From the
wounding place, the stem rotted off and split in two (Figure 3). Both stem and leaf
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