A survey was made on the occurrence of soilborne Phytophthora species in 35 oak stands on a range of geologically different sites in Bavaria. The most widespread species were P. quercina, P. cambivora and P. citricola. Seven other Phytophthora species were isolated infrequently. The fine root systems of 106 healthy and 111 declining mature trees of Quercus robur and Q. petraea were intensively investigated. The results indicate that, depending on the site conditions, at least two different complex diseases are referred to under the name ‘oak decline’. On sites with a mean soil pH (CaCl2)  3·5 and sandy-loamy to clayey soil texture Phytophthora spp. were commonly isolated from rhizosphere soil, and highly significant correlations existed between crown transparency and various root parameters. Oaks with P. quercina or other Phytophthora spp. in their rhizosphere had markedly higher levels of fine root damage than oaks without Phytophthora spp., and were subject to a relative risk of severe crown symptoms of 2·1 and 2·8, respectively. In contrast, in stands with sandy to sandy-loamy soils and a mean soil pH  3·9, Phytophthora spp. were not found. In these stands, correlations between crown transparency and various root parameters were either less significant or not significant. It is concluded that Phytophthora species are strongly involved in oak decline on sandy-loamy to clayey sites with a mean soil-pH (CaCl2)  3·5.

https://bsppjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3059.2000.00521.x

Involvement of soilborne Phytophthora species in Central European oak decline and the effect of site factors on the disease

▪ Abstract Recognition is the earliest step in any direct plant-microbe interaction. Recognition between Phytophthora pathogens, which are oomycetes, phylogenetically distinct from fungi, has been studied at two levels. Recognition of the host by the pathogen has focused on recognition of chemical, electrical, and physical features of plant roots by zoospores. Both host-specific factors such as isoflavones, and host-nonspecific factors such as amino acids, calcium, and electrical fields, influence zoospore taxis, encystment, cyst germination, and hyphal chemotropism in guiding the pathogen to potential infection sites. Recognition of the pathogen by the host defense machinery has been analyzed using biochemical and genetic approaches. Biochemical approaches have identified chemical elicitors of host defense responses, and in some cases, their cognate receptors from the host. Some elicitors, such as glucans and fatty acids, have broad host ranges, whereas others such as elicitins have narrow host ranges. M...

Molecular basis of recognition between phytophthora pathogens and their hosts

Advances in research on oomycete root pathogens

Here, a conceptual model is presented for the development of Phytophthora disease in pedunculate oak. The model is presented using the causal loop diagram tool and gives an overview of how various abiotic and biotic factors, such as soil moisture, nutrient availability and mycorrhizal colonization, may affect the reproduction and the infective capacity of soil-borne Phytophthora species, the susceptibility of the host and subsequent disease development. It is suggested that the link between the root damage caused by Phytophthora species and overall tree vitality is in the assimilation and allocation of carbon within the plants. The potential impact of environmental factors on these processes is discussed. The model is presented with reference to scenarios related to variation in soil moisture and nutrient availability. The need for species-specific validation of the model and the implications of the model are discussed.

A conceptual model for the development of Phytophthora disease in Quercus robur

Soybean isoflavones trigger a calcium influx in Phytophthora sojae.

The effect of added calcium on the developmental fate of encysted zoospores was studied in four strains of Phytophthora sojae. Cysts from all strains were capable of producing both secondar...

Chang Xu

Papers

External calcium controls the developmental strategy of Phytophthora sojae cysts