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The genus Phytophthora, with 326 species in 12 phylogenetic clades currently known, includes many economically important pathogens of woody plants. Different Phytophthora species often possess a hemibiotrophic or necrotrophic lifestyle, have either a broad or narrow host range, can cause a variety of disease symptoms (root rot, damping-off, bleeding stem cankers, or blight of foliage), and occur in different growing environments (nurseries, urban and agricultural areas, or forests). Here, we summarize the available knowledge on the occurrence, host range, symptoms of damage, and aggressiveness of different Phytophthora species associated with woody plants in Nordic countries with a special emphasis on Sweden. We evaluate the potential risks of Phytophthora species to different woody plants in this geographical area and emphasize the increasing threats associated with continued introduction of invasive Phytophthora species. [ABSTRACT FROM AUTHOR]

Diplodia sapinea is a common forest pathogen on Pinus spp. in a large part of the world. In 2013, disease caused by this pathogen on Scots pine (Pinus sylvestris) trees in Sweden was reported for the first time. In this study, we report the first detection of D. sapinea on diseased seedlings of P. sylvestris from two Swedish forest nurseries. Infected seedlings were collected July-November 2019. Diplodia sapinea was identified by morphological characteristics of fungal structures on plant tissues and from culture grown on Hagem agar media, followed by sequencing of fungal ITS rDNA. The result emphasizes the susceptibility of P. sylvestris seedlings. More research is needed to better understand the risk for disease spreading within forest nurseries and into the forest through infected plant material. [ABSTRACT FROM AUTHOR]

Common ash (Fraxinus excelsior L.) is a tree species of significant ecological and economic importance that has suffered a devastating decline since the 1990s in Europe. Native ash species are being threatened by the alien invasive fungus Hymenoscyphus fraxineus, which causes ash dieback. The main goal of the study was to develop markers for traits related to tolerance to ash dieback and to investigate whether genotypes selected for tolerance were genetically different from susceptible wild populations. We phenotyped 326 ash trees from Sweden for disease severity and genotyped them using 63 amplicon-derived single-nucleotide polymorphism (SNP) markers derived from genes in 40 scaffolds spanning 8 MB in total, which represents approximately 1% of the ash genome. We used a mixed linear model to test for an association between genotypic variation at these loci and disease severity of ash. In total, two SNPs were found to have significant associations. One non-synonymous SNP associated with the disease severity of ash was found in a gene predicted to encode a subtilisin-related peptidase S8/S53 domain. A second marginally significant marker was associated with an LRR gene. Our results demonstrate an inexpensive time-effective method for generating genomic data that could have potential for use in future tree breeding programs and provide information for marker-assisted selection. Our study also showed a low differentiation between genotypes selected for disease tolerance and the wild population of ash representing a range of susceptibilities to ash dieback, indicating opportunities for further selection without significantly losing genetic diversity in the ash population. [ABSTRACT FROM AUTHOR]

The aim of the present work was to determine the identity and molecular relationships between 127 strains of dark septate (DS) fungi isolated from healthy root tips, decayed coarse roots, live healthy-looking stems, coarse (stumps, snags and logs) and fine (tree branches and tops) woody debris in temperate-boreal forests in Sweden and Lithuania. Sequence analysis of ITS rDNA was used to identify the fungi. In a neighbour-joining similarity tree, all sequences were grouped into five distinct clusters. Within each of these, ITS rDNA sequence variation consisted of 2-18 nucleotides, corresponding to 1-3% of their total length. The four least variable clusters were supported with high bootstrap values of 86-100%. Comparisons with the sequences in the GenBank database showed that all our strains had a 95-100% homology with identified Phialocephala species, and they were thus assigned to this genus. The representatives of two clusters were identified, as P. fortinii and P. dimorphospora. The representatives of three remaining clusters were defined as Phialocephala sp. 35, Phialocephala sp. 6 and Phialocephala sp. 18. Within each of these clusters, ITS rDNA sequence uniformity was higher than that observed within P. fortinii and P. dimorphospora. Consequently, their clusters were most discrete, supported with bootstrap values of 100%. Genetic variation in the five distinguished Phialocephala species and their possible ecological roles are discussed. Phialocephala sp. 6 was confined to healthy root tips of conifers. P. dimorphospora was only associated with dead woody tissue of P. abies. P. fortinii, Phialocephala sp. 18 and sp. 35 were isolated from both dead and living conifers and Betula pendula. In conclusion, the present study revealed the ability of fungi from the genus Phialocephala to colonise and persist in live and dead trees under strikingly different ecological conditions.