Characteristics of Hendersonia on Pinus mugo Needles Primarily Infected with Lophodermella sulcigena in the Tatra Mountains

For several years, an intense needle disease of Pinus mugo, caused by Lophodermella sulcigena, has been occurring in the Polish Tatra Mountains. These needles are secondarily colonized by a fungus of the genus Hendersonia. Phylogenetic analyses placed the Polish isolates together with North American sequences deposited in GenBank as Hendersonia pinicola. However, a major limitation of this comparison is the current lack of an authentic sequence of H. acicola, a sequence from the holotype of H. pinicola, and adequate morphological documentation for the published accessions. To date, no fungus species with morphological characteristics typical of H. pinicola has been documented in Europe. In the current study, detailed morphological and extended molecular analyses were undertaken on Hendersonia colonizing P. mugo needles in the Tatra Mts. For eight representative in vivo samples and eight in vitro isolates, conidia size was measured, the proportion of conidia was calculated according to the number of transverse septa, and the presence of constrictions at the septa was recorded. The conidia of the analyzed Hendersonia reached a wide range of dimensions from 9–23 × 3–7 (14.6 × 4.9) µm, but the proportion of conidia above 15 µm was sparse. Conidia produced zero to five transverse septa, but conidia with two septa predominated (69.0%). Most conidia showed more or less pronounced constrictions at the septa. The morphological characteristics of this fungus do not provide any basis for its classification as Hendersonia pinicola Wehm. Most morphological characteristics support affiliation Polish isolates to Hendersonia acicola Münch & Tubeuf. The nucleotide sequences for four gene fragments from six representative H. acicola cultures were determined and deposited in GenBank (18S; ITS, 28S rRNA, and TEF1). A preliminary in vitro dual culture assay was used to assess the antagonistic properties of six H. acicola isolates against ten fungal species isolated from P. mugo needles. The most common finding was an inhibition zone between the colonies (81.7% of dual cultures). The dual culture assays indicate antagonistic activity of H. acicola against several needle-associated fungi and justify further testing of its interactions with pine needle pathogens under more natural conditions.