Addition to the EPPO Alert List - Phytophthora quercina: a new species found on declining oaks
Oak decline is a complex syndrome attributed to several biotic and abiotic causes (insects, fungi, poor soil fertility, drought, pollution etc.) which has been observed for many years in Europe. Although pathogens are generally not considered as the primary cause of oak decline, many fungal species have been found on declining oaks, for example: Diplodia, Hypoxylon, Cylindrocarpon, Phoma, Ophiostoma/Ceratocystis, Armillaria, Phellinus, Phytophthora. In a three-year study, roots of declining and healthy oak trees (Quercus robur, Q. petraea, Q. cerris, Q. pubescens, Q. ilex) collected from 33 stands (in Germany, Switzerland, Hungary, Slovenia, Italy and France) were examined for the presence of Phytophthora species. Several Phytophthora species were isolated from most oak stands: P. citricola, P. cactorum, P. cambivora, P. gonapodyides, P. undulata and two unknown species. One of these unknown species was frequently isolated from necrotic fine roots and rhizosphere soil containing fine roots of all 5 oak species from various sites in Germany, Hungary, Italy and France. It was not found in samples from Slovenia and Switzerland. This unknown species has been described as a new species: Phytophthora quercina. Molecular studies have also confirmed its distinctness from other Phytophthora. Pathogenicity tests carried out with infested soil and Q. robur seedlings showed that isolates of P. quercina induced severe dieback, root necrosis and leaf chlorosis. Among Phytophthora species tested, P. quercina was the most pathogenic.
Phytophthora quercina: a new species found on declining oaks
Why: Phytophthora quercina came to our attention because it has recently been described as a new species, pathogenic to oak, and involved in oak decline in some countries.
Where: EPPO region: France, Germany, Hungary, Italy.
On which plants: Quercus species (e.g. Quercus robur, Q. petraea, Q. cerris, Q. pubescens, Q. ilex)
Damage: Oak decline. In pathogenicity tests, Q. robur seedlings showed severe dieback, root necrosis, leaf chlorosis.
Dissemination: More data needed.
Pathway: Plants for planting of Quercus from countries where P. quercina occurs.
Possible risks: Oaks are important amenity and forest trees in the EPPO region. P. quercina is apparently pathogenic to oaks and not present in all parts of the EPPO region. But more data is needed on its biology and particularly on its pathogenicity and its role in oak decline.
EPPO RS 2000/066
Panel review date - Entry date 2000-04
Sources
Cooke, D.E.L.; Jung, T.; Williams, N.A.; Schubert, R.; Bahnweg, G.; Osswald, W.; Duncan, J.M. (1999) Molecular evidence supports Phytophthora quercina as a distinct species. Mycological Research, 103(7), 799-804.
Jung, T.; Cooke, D.E.L.; Blaschke, H.; Duncan, J.M.; Osswald, W. (1999) Phytophthora quercina sp. nov., causing root rot of European oaks. Mycological Research, 103(7), 785-798.