A b s t r a c tThe present paper presents the results of long-term observations of differences in growth and morphology of colonies of C. fraxinea isolated from ash stems with symptoms of dieback and the results of studies on effects of temperature on growth and morphology of colonies in vitro. Thirty randomly chosen C. fraxinea cultures, originating from six Forest Districts in southern and northern Poland, viz. Andrychów, Gryfice, Kańczuga, Lębork, Miechów and Mircze, were included in the temperature assay. Colony growth and morphology were evaluated in vitro, on malt extract agar. Two replicates of each isolate were incubated at 5, 10, 15, 20, 25 and 30 o C in darkness. Colonies of C. fraxinea isolated from necrotic stem tissues of diseased ash trees differed greatly in colour, structure, growth rate, presence of sectors and stromata as well as the intensity of conidial sporulation. Colony characters were often lost in further sub-cultures grown on the same medium. Colonies of C. fraxinea grew at 5-25 o C in vitro. Three isolates still grew, though slowly, at 30 o C. The optimum temperature for growth was 20 o C. Among 30 isolates tested, five grew most quickly at 25 o C and four at 15 o C. Differences among colony diameters recorded at 5, 10, 15, 20 and 30 o C were statistically significant, while differences at 15 and 25 o C were not. At some temperatures, statistically significant differences in growth rate were related to the origin of the isolates. There were three main colony colour types. Temperature was the main factor affecting colony morphology in vitro. The formation of sectors was observed in 36% of colonies, pseudoparenchymatous stromata in 10.4% of colonies, and white crystalline substances in 53.3% of colonies. The results of in vitro observations were used for discussion of the effects of temperature on growth and activity of C. fraxinea in vivo.

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Summary Leptomelanconium allescheri was identified for the first time in Poland in 2016 in the Tatra Mts. on Pinus mugo needles. It produced numerous conidiomata on necrotic lesions on live needles. In our study, we provide detailed characteristics of disease symptoms and describe morphology of the structures of the fungus. The shape and size of macroconidia are proven to be more variable in vitro than in situ. The malt extract agar colonies of the fungus obtained from germinating macroconidia are described for the first time. Our observations prove also that, apart from macroconidia, L. allescheri produces in vitro unicellular, hyaline microconidia, 3.5–10 × 1.8–5.0 μm in size, the previously unknown aspect in the development cycle of this species. The BLAST search with ITS and LSU sequences of L. allescheri resulted in the closest match with Cenangium acuum accessions (94%–95% and 99%, respectively). Two gene based, LSU plus ITS, phylogenetic positioning of L. allescheri proves that it belongs to Pezizomycotina, Helotiales. Further, on family level, placement of L. allescheri, as well as its two closest species C. acuum and Piceomphale bulgarioides, remains undefined. The L. allescheri barcode sequences (accession numbers: ITS—, LSU—, IGS—) and cultures were submitted to NCBI GenBank and CBS Utrecht, The Netherlands culture collection.

Dwarf mountain pine, Pinus mugo, is an important component of the subalpine and alpine zone in Europe. For several years, in one of the natural areas of the occurrence of this species in the Polish Tatras, an intensified decline of the assimilation apparatus has been observed. The studies conducted in 2016–2020 were aimed at determining the types of disease symptoms occurring on P. mugo needles and at identifying the species composition of fungi within symptomless and diseased needles. We isolated 57 taxa from 6 types of disease symptoms and from needles without disease symptoms, identified on the basis of morphological features and molecular analyses. Absolute parasites were represented by only one species of Coleosporium senecionis, which was identified by the aecium stage. The genus Lophodermium was represented by three species: L. conigenum, L. corconticum and L. pini-mugonis. So far, L. corconticum was known only from the Karkonosze Mountains in Poland, and L. pini-mugonis from the German Alps. In addition, the more frequently isolated species included: Sydowia polyspora, Hendersonia sp., Nemania serpens, Leptomelanconium allescheri, Cladosporium spp., Biscogniauxia nummularia and Alternaria spp. Some taxa were associated with only one type of disease symptom, while some species of fungi were found to be associated with different symptoms. Twelve species of fungi were isolated from living symptomless needles, some of which were subsequently found in association with nectrotic areas on needles, e.g., Lophodermium corconticum, L. conigenum and Leptomelanconium allescheri. L. pinastri has not been found in the present studies. In the discussion, an attempt was made to assess the role of some of the identified species of fungi in causing the disease process of P. mugo needles.

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