Six species of Ceratocystis (Ceratocystis grandicarpa, Ceratocystis introcitrina, Ceratocystis moniliformis, Ceratocystis piceae, Ceratocystis prolifera and Ceratocystis stenoceras) found earlier in Southern Poland in middle-aged and old oak stands showing the decline symptoms were used for pathogenicity tests. The fragments of their mycelium producing spores on malt agar were inoculated into the wounds on branches and stems of 16-year-old Qercus robur (inoculation - July 1988, reisolation - November 1989), and stems and roots of 5-year-old dormant trees (inoculation - May 1989, reisolation - November 1989). The brown discoloration of xylem within, below and above the wound for a distance up to 21cm, was a most characteristic internal symptom (Tables 1-3). The discoloration occurred in trees inoculated with Ceratocystis species as well as in the controls. Reisolations showed that many Ceratcystis species may survive in xylem of inoculated trees for a considerably long period of time, and may also spread in it. The initial results did not indicate a significant pathogenicity of tested Ceratocystis species. The decline symptoms appeared only in case of branches inoculated with Ceratocystis prolifera.
