THE CONDITION OF THE PHLOEM IN DECLINING OAKS

Oaks (Quercus petrdea, Q. robur) from several sites in eastern Austria affected by novel oak decline (NOD), as well as oaks (Q. robur) showi ng symptoms of oak yellows (OY), were tested for the presence of mycop lasma-like organisms (MLOs). The samples, comprising roots, annual sho ots, and branches, were examined using light-, fluorescence, and elctr on-microscopic techniques. Staining with the DNA-fluorochrome DAPI pro vided no evidence for the presence of MLOs in any of the samples. Furt hermore, no pathological sieve-tube necrosis and no abnormal callose a ccumulation could be observed. An association of MLOs with 'novel oak decline' or 'oak yellows' is, therefore, unlikely.