sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDÜ Faculty of Forestry Journal
In poplars, the pathogen played only a secondary role for a long time because
poplar cultures were less important for timber industry in Germany. In other
countries like New Zealand, Sweden, and Romania, observations of P. syringae
were made on poplars for a long time (Spiers, 1990; Ramstedt et al., 1994; Mocanu
& Poleac, 1965). The pattern of damages that was described were spotted leaves,
wilting of leaves and shoots in the whole, as well as bark necroses. In current
investigations in a Chinese poplar breeding program P. syringae pv. syringae was
identified as the reason for injuries like bark necroses on cuttings of various hybrid
clones (Xiang et al., 2001). Moreover, this species could be found in symptomless
hybrid clones of different poplar sections (Ulrich et al., 2008).
The disease transmission of the pathogen is unclear until now. Possibly
mechanical bark wounds induced by insects and other animal vectors are
responsible, considerably earlier in summer. The invasion of bark tissue is also
possible by bark micro-cracks following weather conditions like summer drought
or autumn frost. The propagation of the pathogen takes place within a large
temperature range and can still be found slightly above zero. Sequent changing of
warm and cold periods with freeze stress could have promoted the infection by the
pathogen and their distribution within the tissue. The formation of necroses in the
cold season can be caused by pathovars belonging to ice nucleation inducing
strains of P. syringae. Those pathotypes are able to induce the formation of ice
crystals within plant cells downward from -1°C. As a result, the cell walls burst and
the protoplasm can serve as nutrient resources for further bacteria growth.
Moreover, some pathovars of the P. syringae group are known as phytotoxine
producers. Analysed compounds are the lipodepsipeptides Syringomycin and
Syringopeptin, possessing a cell wall destroying influence (Hutchinson and Gross,
1997).
In recent time, poplars became more important as a fast growing tree species for
biomass production in short rotation coppice plantations, and a high demand for
suited propagation material exists. A basic precondition of utilizing poplar for this
purpose is the provision of proved propagation material with high quality and free
of harmful organisms. The use of cuttings grown in infected stock plant cultures
can lead to a fast distribution of the disease. It is difficult to appreciate a possible
role of P. syringae as a serious pathogen for poplar cultures in Germany.
Therefore, work on epidemiology, vectors, and host-specific association of various
pathovars is recommended as well as research referring to resistance /
susceptibility of clones and cultivars of economical importance.
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