Fungicide-Resistant Botrytis in Forest Nurseries May Impact Disease Control in Norway Spruce.

Gray mold, caused by Botrytis spp., is a serious problem in Norway spruce seedling production in forest nurseries. From 2013 to 2019, 125 isolates of Botrytis were obtained from eight forest nurseries in Norway: 53 from Norway spruce seedlings, 16 from indoor air, 52 from indoor surfaces, and four from weeds growing close to seedlings. The majority of isolates were identified as B. cinerea, and over 60% of these were characterized as Botrytis group S. B. pseudocinerea isolates were obtained along with isolates with DNA sequence similarities to B. prunorum. Fungicide resistance was assessed with a mycelial growth assay, and resistance was found for the following: boscalid (8.8%), fenhexamid (33.6%), fludioxonil (17.6%), pyraclostrobin (36.0%), pyrimethanil (13.6%), and thiophanate-methyl (50.4%). Many isolates (38.4%) were resistant to two to six different fungicides. A selection of isolates was analyzed for the presence of known resistance-conferring mutations in the cytb, erg27, mrr1, sdhB, and tubA genes, and mutations leading to G143A, F412S, ΔL497, H272R, and E198A/F200Y were detected, respectively. Detection of fungicide resistance in Botrytis from Norway spruce and forest nursery facilities reinforces the necessity of employing resistance management strategies to improve control and delay development of fungicide resistance in the gray mold pathogens.[Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Oomycete Soil Diversity Associated with Betula and Alnus in Forests and Urban Settings in the Nordic-Baltic Region.

This study aimed to determine the differences and drivers of oomycete diversity and community composition in alder- and birch-dominated park and natural forest soils of the Fennoscandian and Baltic countries of Estonia, Finland, Lithuania, Norway, and Sweden. For this, we sequenced libraries of PCR products generated from the DNA of 111 soil samples collected across a climate gradient using oomycete-specific primers on a PacBio high-throughput sequencing platform. We found that oomycete communities are most affected by temperature seasonality, annual mean temperature, and mean temperature of the warmest quarter. Differences in composition were partly explained by the higher diversity of Saprolegniales in Sweden and Norway, as both total oomycete and Saprolegniales richness decreased significantly at higher longitudes, potentially indicating the preference of this group of oomycetes for a more temperate maritime climate. None of the evaluated climatic variables significantly affected the richness of Pythiales or Peronosporales. Interestingly, the relative abundance and richness of Pythiales was higher at urban sites compared to forest sites, whereas the opposite was true for Saprolegniales. Additionally, this is the first report of Phytophthora gallica and P. plurivora in Estonia. Our results indicate that the composition of oomycetes in soils is strongly influenced by climatic factors, and, therefore, changes in climate conditions associated with global warming may have the potential to significantly alter the distribution range of these microbes, which comprise many important pathogens of plants.

A revision of the history of the Colletotrichum acutatum species complex in the Nordic countries based on herbarium specimens.

Herbaria collections containing plants with disease symptoms are highly valuable, and they are often the only way to investigate outbreaks and epidemics from the past as the number of viable isolates in culture collections is often limited. Species belonging to the Colletotrichum acutatum complex infect a range of important crops. As members of the C. acutatum complex are easily confused with other Colletotrichum species, molecular methods are central for the correct identification. We performed molecular analyses on 21 herbaria specimens, displaying anthracnose symptoms, collected in Norway and Denmark before the first confirmed findings of C. acutatum complex members in this region. Sequencing parts of the fungal ITS regions showed that members of the species complex were present in 13 of the 21 specimens collected in different parts of Norway and Denmark between 1948 and 1991, representing seven plant hosts (three cherry species, apple, raspberry and rhododendron). This is the first time herbarium specimens have been used to study these pathogens under Nordic conditions. Differences in the ITS sequences suggest the presence of different genotypes within the complex, indicating a well-established population.

Relative Contribution of Various Sources of Botrytis cinerea Inoculum in Strawberry Fields in Norway.

To identify the most important sources of inoculum of Botrytis cinerea (causal agent of gray mold) in commercial strawberry (Fragaria × ananassa) fields in Norway, soil and overwintered plant material were collected from planting beds and alleys at five locations in 2000 to 2002 (13 samples altogether). Plant material was sorted by category (e.g., leaves, stems, mulch, and weeds). After subsamples of each material were incubated for 5 days at 20°C at high humidity, conidiophores of B. cinerea growing from mycelia and sclerotia were counted. Overwintered plant debris within planting beds yielded more than 96% of total conidiophores counted, the remainder originating from plant debris collected from alleys or soil. Overwintered strawberry plant debris produced 98% of the conidiophores within planting beds and 80% of the conidiophores in the alleys, while the remaining was produced by weeds. Senescing and dead leaf laminae produced 45% of the conidiophores while stem residues (i.e., petioles, stolons, inflorescences, and unidentifiable stem parts) produced 50% and mummified fruit produced 5% within planting beds. The contribution of sclerotia, compared with mycelia, to conidiophore production varied greatly between fields and years. Overall, 47% of the total number of conidiophores produced in plant material within planting beds originated from sclerotia. More than 90% of the conidiophores from sclerotia were found in dead stem residues.