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Summary

Oaks (Quercus petraea, Q. robur) from several sites in eastern Austria affected by novel oak decline (NOD), as well as oaks (Q. robur) showing symptoms of oak yellows (OY), were tested for the presence of mycoplasma-like organisms (MLOs). The samples, comprising roots, annual shoots, and branches, were examined using light-, fluorescence-, and electron-nucroscopic techniques. Staining with the DNA-fluorochrome DAPI provided no evidence for the presence of MLOs in any of the samples. Furthermore, no pathological sieve-tube necrosis and no abnormal callose accumulation could be observed. An association of MLOs with‘novel oak decline’ or ‘oak yellows’ is, therefore, unlikely.