First report of Phytophthora quercina from oak forests in Austria

Phytophthora quercina Jung, a causal agent of root rot on Quercus spp. in Europe (Jung et al., 1999) was isolated from mature oak stands in the eastern part of Austria during surveys carried out in 1999 and 2000. The pathogen has been reported from Germany, Italy, Hungary, France and Turkey (Jung et al., 1999; Balcý & Halmschlager, 2002). In Austria it was recovered from Q. robur, Q. petraea and Q. pubescens. Isolates were primarily obtained from rhizosphere soil samples including necrotic fine roots, which were collected around the stem base of healthy as well as declining oak trees

Young oak leaves were used as bait to isolate Phytophthora spp. from flooded soil samples. Leaves showing discoloration were plated on selective medium PARPNH (pimaricin, ampicillin, rifampicin, pentachloronitrobenzene, nystatin and hymexazol). Identification of isolates was based on cultural and morphological features and on comparisons with authentic cultures. P. quercina was the most common species and occurred on 11 of 35 sites (32%). The sequences (2 isolates) and restrictions digest patterns (9 isolates) of the internal transcribed spacer (ITS) regions of rDNA from Austrian P. quercina were identical. The digest patterns matched those of Italian, Hungarian and German strains (Cooke et al., 1999; D. Cooke, pers. comm.), including the aggressive strains used by Jung et al. (1999) for inoculation tests, although pathogenicity tests were not carried out on Austrian isolates. Other Phytophthora species, recovered less frequently, included P. citricola, P. syringae, P. gonapodyides and P. europaea.

The results are consistent with similar studies in oak forests in Germany, where P. quercina was found to be the most frequent species among a diverse assemblage of Phytophthora spp. thought to be involved in the oak decline syndrome (Jung et al., 2000). In inoculation tests P. quercina proved to be one of the most aggressive species to roots of Q. robur seedlings (Jung et al., 1999). Our isolation results indicate that P. quercina shows high plasticity concerning site conditions, since it was even obtained from dry sites that normally do not favour the survival of Phytophthora spp. The results of this study suggest that P. quercina is widely distributed in oak forests in Austria and may play an important role in the oak decline in certain oak ecosystems in Austria.