The sooty blotch and flyspeck (SBFS) syndrome of apples and other fruits is caused by a complex consortium of epiphytic fungi that colonize the fruit cuticula. SBFS fungal strains isolated from apples were screened for growth inhibition of the phytopathogen Colletotrichum fioriniae in dual culture tests. Extracts of 11 isolates of SBFS fungi (Microcyclospora malicola, Microcyclospora pomicola, Microcyclospora tardicrescens, and Microcyclosporella mali) inhibited growth of the test strains and were studied for production of antibiotics. A strain of Microcyclospora tardicrescens strongly inhibited growth and was cultivated on a larger scale to characterize its secondary metabolites. Bioassay-guided fractionation and subsequent structure elucidation by spectroscopic and spectrometric methods (NMR, HRMS) yielded trichothecolone acetate (1) and its novel derivative (S)-7-hydroxytrichothecolone acetate (2) as active principles. Microcyclospora tardicrescens was thus identified as a producer of the hazardous trichothecene type mycotoxins for the first time, which should give reason to monitor these foodborne fungi more carefully in the future.

Introduction !Various members of the Ascomycetes order Capnodiales are known to form mycelial mats or fruiting bodies on the surface of epicuticular wax layers of apples that result in dark, flyspeck-like spots and sooty blemishes [1]. Although these fungi do not cause fruit destructing diseases or rots, sooty blotch and flyspeck (SBFS) fungi cause substantial economic damages. Stored apples may desiccate earlier during storage, and apples with dark smudges and blemishes have a reduced market quality [2]. Although sooty blotch fungi have early been associated with different kinds of mycelial types, only three species were distinguished as causal agents until the end of the 20th century [3]. A single species only was accepted as the causal agent of flyspeck. This situation changed dramatically when polyphasic taxonomic studies incorporated DNA sequence-based species recognition concepts, with the help of which at least 60 SBFS fungi were distinguished and numerous new species and genera described [4-6].Although different SBFS species can co-occur in the same orchard and even on the same apple, details of how they interact between each other or to host substrata and other fruit pathogens are hitherto little understood. During inventory studies for SBFS fungi in Slovenia, we observed that juxtaposed colonies of different SBFS fungi were clearly separated from each other on field-collected apples and that a selected strain of Microcyclospora tardicrescens inhibited the colony growth of the fruit pathogen Colletotrichum fioriniae in dual culture tests [7]. Bioassay-guided fractionation and subsequent structure elucidation yielded trichothecolone acetate and its novel (S)-7-hydroxy derivative as active principles for the interaction between M. tardicrescens and C. fioriniae. In this follow-up publication, we describe the investigation of an isolate of another sooty blotch species, Microcyclospora malicola, and its production of a series of bioactive pigments. Abstract !A multitude of sooty blotch and flyspeck fungi, mainly belonging to the Ascomycetes order Capnodiales, causes dark blemishes and flyspeck-like spots on apples worldwide. Different sooty blotch and flyspeck fungi can coexist in the same orchard and even on a single fruit. Our preceding experiments revealed an activity of Microcyclospora malicola strain 1930 against the anthracnose fungus Colletotrichum fioriniae in dual culture assays. Extracts of M. malicola strain 1930 showed a broad bioactivity against filamentous fungus Mucor hiemalis and gram-positive bacterium Bacillus subtilis. A bioactivity-guided isolation led to the identification of obionin A (1) as the main active principle. In addition to 1, which was previously isolated from the marine fungus Leptosphaeria obiones, we isolated three derivatives. Metabolite 2 bears a keto function at C-6, besides the replacement of oxygen by nitrogen at position 10. Two more derivatives are adducts (3, 4) of acetone as work-up artifacts. Because obionin A (1) and its derivative 2 showed cytotoxic effects and...

Adopting the currently used concept for the genus Peltaster, the sooty blotch fungus Peltaster cerophilus is newly described from the cuticle of ripening or ripe apples. It forms a punctate phenotype consisting of superficially formed pycnothyria and a superficial mycelial mat consisting of a net of brown or brownish black hyphae. The pycnothyria are olivaceous brown to brown but have a spot in the center that is less strongly pigmented. Pycnothyria on the holotype of P. fructicola are homogeneously pigmented. On synthetic nutrient-poor agar, P. cerophilus is largely indistinguishable from P. fructicola. It forms delicate, spreading hyphae and intercalary conidiogenous cells with short, lateral, apically thick-walled conidiogenous necks forming blastic, unpigmented, one-celled conidia in basipetal succession. Conidia can swell and become one-septate. The species has microcyclical conidiation in proximate parts of colonies. DNA sequence analyses based on the ITS and the partial nuclear small and large subunit ribosomal RNA genes, the partial mitochondrial small subunit rRNA gene and the partial translation elongation factor 1-α gene support the distinction of the European P. cerophilus from P. fructicola, which is known from North America and Europe. The nuclear small ribosomal RNA subunit gene sequences of P. cerophilus contain two group I introns at locations known to accommodate introns in certain other, unrelated taxa. One of these, for which the code "SSU-1506 intron" was adopted, is 1459 base pairs long and located between the universal primer sites ITS5 and ITS1. Similar or positional-differing introns were encountered also in three currently undescribed Peltaster species. Representative strains of Peltaster fructicola did not accommodate introns in the nuclear small subunit ribosomal RNA gene.