sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDÜ ORMAN FAKÜLTESİ DERGİSİ
The findings of the study show some morphological characteristics of Eutypella
canker that help in understanding the disease spread. The very high average
ascospore discharge of 506,000 ascospores cm –2 h –1 , or 1.0 billion ascospores h –1
for the whole canker area is important for the success of disease spread. The study
of the isolates showed that E. parasitica is the dominant fungus in infected and
decayed wood. The fungus has proven its pathogenic ability with progressive
attack tactics where the maple rarely has a chance to protect itself with callus or
wound-wood. The Eutypella canker grows faster in longitudinal direction that in
transverse direction. Therefore, the canker shape is in most cases almost regular or
elongated oval. When the maple succeeds in defending itself from the fungus by
forming wound-wood, the fungus can reinfect the wound-wood and bark from the
underlaying wood. When the host is killed or snapped due to canker progress, the
fungus acts as a saprobe and continues to produce ascospores for some years. The
disadvantages of the fungus are its heavy ascospore octads which are disseminated
only over short distances and the fact that they can infect only exposed xylem that
occurs up to 4 m from the ground level.
When a disease is introduced to a new distant location, e.g. another continent, it
is hard to predict disease behavior and its spread speed. Environmental conditions
could be more favorable for the disease and thus it could accelerate its spread rate.
In a new environment new vectors of the disease could be present which could also
add to the success of disease spread. A third factor that could help the disease to
spread and establish are hosts. In a new environment new hosts are possible and
host distribution can be over a wider area and contiguous. A new host, i.e. the field
maple, was found and described in Slovenia (Ogris et al., 2005), but there are
numerous other possible hosts (Acer spp.) present in Europe that have not yet been
identified. There are at least 10 autochthonous maple species in Europe that could
be the target of E. parasitica (Ogris et al., 2006). An inoculation study should be
planned and carried out to test possible susceptibility. The results of that study
would give needed information for more accurate assessment of the disease spread
risk.
Eutypella canker has been recognized as a new disease of maple in Europe.
Despite intensive searching by the Slovenian Forestry Service only 225 Eutypella
cankers were found from 2005–2009. We suspect that there are many undetected
cases of Eutypella canker. Since it is assumed that cankers are present for a longer
time period and they are dispersed over wide area we do not believe that the
eradication of the disease is possible (Jurc et al., 2005). The disease can also have
an economical impact. Incidence of the canker in North America is usually less
than 5% (Gross, 1984b). Stands with over 10% of maples cankered were fairly
common, and instances of over 40% cankering have been observed; in Slovenia
there was a case with almost 29 % incidence. The disease frequently kills trees less
than 7.5 cm in diameter and larger trees are predisposed to wind snap at the canker
(French, 1969; Kliejunas and Kuntz, 1974). Cankered trees lose up to 50% of their
merchantable cubic volume because most of the cankers occur below a height of 3
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