Diversity, phylogeny and control strategies of Phytophthora species from declining Fagaceae Mediterranean forests

In Europe, tree species belonging to the family Fagaceae dominates a wide range of habitats, including sclerophyllous forests of the Mediterranean basin and the deciduous communities of mountainous and low land areas. These species play a relevant ecological role since they are considered keystone species in forest ecosystems. They also have an economic importance, providing a wide range of goods, i.e., biomass, fiber, wood products and food. However, since the early 1990s a recrudescence of decline phenomena associated with Phytophthora species was reported throughout the European countries. This thesis was aimed at i) study the diversity of Phytophthora species in Fagaceae forests, with particular regards to cork oak and chestnut stands, ii) develop new control strategies to control disease caused by Phytophthora spp., iii) undertake a population study based on multigene analyses using P. quercina as model. Cork oak decline has increased over the last decades mainly due to the spread of Phytophthora species associated to this syndrome. In this study, rhizosphere soil samples were collected from 39 different sites and analyzed using the baiting technique. In addition, the in-situ river baiting technique was used in 10 different water systems running within the surveyed cork oak stands. In total 14 different Phytophthora species were isolated; the pathogenicity of these species was assessed using soil infestation and log inoculation techniques. Ink disease caused by Phytophthora spp. still represents a serious threat to sweet chestnut throughout its distribution area. We tested in planta the effectiveness of trunk injection with K-phosphonate against seven different Phytophthora species associated with ink disease. The results obtained demonstrated that K-phosphonate was able to contain the development of Phytophthora infection in phloem tissues. However, its effectiveness varied based on the concentration applied and the Phytophthora species tested. Overall, this study broadens the knowledge on endotherapic treatments with K-phosphonate as an effective measure for the management of chestnut ink disease. Interestingly, the size of the lesions caused by P. cinnamomi were directly correlated with mean temperature. Since distinct morphological phenotypes were observed amongst the isolates of the oak-specific pathogen P. quercina, detected from oak trees in Europe, morphological and phylogenetical analyses were conducted to assess the intraspecific variability of P. quercina. Overall, 64 different isolates of P. quercina from several European countries and oak species were analysed. Colony morphology and growth rates were compared, and nuclear and mitochondrial DNA sequences were investigated by phylogenetical analyses. The results show a high variability within the P. quercina population both in terms of colony features and growth rates. The phylogenetical analyses (Bayesian Inference and Maximum Likelihood) have enabled discrimination of 12 different lineages into the European P. quercina population, with clear association between host and geographic area. In addition, a putative new species, closely related to P. quercina, was isolated from Chamaecyparis lawsoniana var. globosa in Croatia. Further studies are needed to characterize and officially describe this new taxon in Clade 12.

In Europe, tree species belonging to the family Fagaceae play a relevant ecological role since they are considered keystone species in forest ecosystems. However, since the early 1990s a recrudescence of decline phenomena associated with Phytophthora species was reported throughout the European countries. Cork oak decline has increased over the last decades mainly due to the spread of Phytophthora species associated to this syndrome. In this study, rhizosphere soil samples were collected from 39 different sites and analyzed using the baiting technique. In addition, the in-situ river baiting technique was used in 10 different water systems running within the surveyed cork oak stands. In total 14 different Phytophthora species were isolated. Ink disease caused by Phytophthora spp. still represents a serious threat to sweet chestnut throughout its distribution area. We tested in planta the effectiveness of trunk injection with K-phosphonate against seven different Phytophthora species associated with ink disease. The results obtained demonstrated that K-phosphonate was able to contain the development of Phytophthora infection in phloem tissues. However, its effectiveness varied based on the concentration applied and the Phytophthora species tested. Interestingly, the size of the lesions caused by P. cinnamomi were directly correlated with mean temperature. Since distinct morphological phenotypes were observed amongst the isolates of P. quercina, morphological and phylogenetical analyses were conducted to assess its intraspecific variability. Overall, 64 different isolates of P. quercina from several European countries and oak species were analysed. The analyses conducted show a high variability within the population, discriminating 12 different lineages, with clear association between host and geographic area. In addition, a putative new species, closely related to P. quercina, was isolated from Chamaecyparis lawsoniana var. globosa in Croatia