Pathogenicity of Swedish isolates of Phytophthora quercina to Quercus robur in two different soils

Abstract

Summary• Several studies have demonstrated the involvement of soil-borne Phytophthora species, especially Phytophthora quercina , in European oak decline. However, knowledge about the pathogenicity of P. quercina in natural forest soils is limited.• The short-term effects of two south-Swedish isolates of P. quercina on root vitality of Quercus robur seedlings grown in two different soils, one high pH, nutrient-rich peat-sand mixture and one acid, nitrogen-rich but otherwise nutrient-poor forest soil are described. Pathogenicity of P. quercina was tested using a soil infestation method under a restricted mesic water regime without prolonged flooding of the seedlings.• There was a significant difference in dead fine-root length between control seedlings and seedlings grown in soil infested with P. quercina . Trends were similar for both soil types and isolates, but there was a higher percentage of fine-root die-back and more severe damage on coarse roots in the acid forest soil. No effects on aboveground growth or leaf nutrient concentration between control seedlings and infected seedlings were found.• The results confirm the pathogenicity of south-Swedish isolates of P. quercina in acid forest soils under restricted water availability. Stress-induced susceptibility of the seedlings and/or increased aggressiveness of the pathogen in the forest soil are discussed as key factors to explain the difference in root die-back between soil types.

Emergent insects, pathogens and drought shape changing patterns in oak decline in North America and Europe

“…P. cinnamomi (widely distributed, with likely origin of Papua New Guinea) is a worldwide invasive pest, one of the most destructive root pathogens, and cold temperatures are thought to limit its distribution (Brasier, 1996). Phytophthora diseases are most prevalent in relatively alkaline, clay-rich soils Jönsson et al, 2005); recent evidence indicates that, contrary to earlier belief, they can also infect roots in acidic soils (Jönsson et al, 2003;Jönsson, 2004). Phytophthora diseases can infect fine roots during periods of excess or limited soil moisture, and may be particularly successful when conditions rapidly change from one moisture extreme to the other (Brasier, 1996;Jung et al, 2003;Jönsson, 2006).…”

CanPhytophthora quercinahave a negative impact on mature pedunculate oaks under field conditions?

“…The most frequently recovered species was P. quercina. Phytophthora quercina was found to cause root infection in oak seedlings, in artificial soil mixtures as well as in acid forest soils, with subsequent necrosis and die-back of the root systems [21,22]. A weak association was also found between the occurrence of P. quercina and the vitality of mature oak stands [23].…”

Pathogenicity of Phytophthora isolates originating from several woody hosts in Bulgaria and Poland

“…In our experiment, it was demonstrated that P. quercina can infect not only fine roots (Jung et al 1999;Jönsson et al 2003) but also tissues of Turkey oak stems. Also, most of the investigated isolates show the ability to grow in the living tissues without causing any visible disease symptoms.…”

“…The pathogenicity of south-Swedish isolates of P. quercina in acid forest soils under restricted water availability was studied by Jönsson et al (2003). They found that in the acid forest soil, the percentage of fineroot dieback was high.…”

“…The soil-borne species Phytophthora quercina T. Jung appears to be strongly involved in the European oak decline phenomenon (Jönsson et al 2003). The species pathogenicity has been studied only on the fine roots of Central European oaks (Jung et al 1999).…”