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.

Chemoenzymatic synthesis of the enantiomer of 4,12-dihydroxysterpurene, the structure assigned to a metabolite isolated from the culture broth of Stereum purpureum.

Compound ent-1 has been prepared by engaging a derivative of the enantiomerically enriched and microbially derived cis-1,2-dihydrocatechol 6 in an intramolecular Diels-Alder reaction, elaboration of the adduct so-formed to the cyclopentannulated bicyclo[2.2.2]octenone 3, and photochemical rearrangement of this to the cyclobutanone 2. By such means it has been established that 4,12-dihydroxysterpurene (1) is not the structure of the natural product isolated by Xie and co-workers from a culture broth of Stereum purpureum.

Biosynthesis of the biphenyl phytoalexin aucuparin in Sorbus aucuparia cell cultures treated with Venturia inaequalis.

Aucuparin is the most widely distributed biphenyl phytoalexin in the rosaceous subtribe Pyrinae, which includes the economically important fruit trees apple and pear. The biphenyl scaffold is formed by biphenyl synthase, which catalyzes biosynthesis of 3,5-dihydroxybiphenyl. Conversion of this precursor to aucuparin (3,5-dimethoxy-4-hydroxybiphenyl) was studied in cell cultures of Sorbus aucuparia after treatment with an elicitor preparation from the scab-causing fungus Venturia inaequalis. The sequence of the biosynthetic steps detected was O-methylation - 4-hydroxylation - O-methylation. The two alkylation reactions were catalyzed by distinct methyltransferases, which differed in pH and temperature optima as well as stability. Biphenyl 4-hydroxylase was a microsomal cytochrome P450 monooxygenase, whose activity was appreciably decreased by the addition of established P450 inhibitors. When fed to V. inaequalis-treated S. aucuparia cell cultures, radioactively labeled 3,5-dihydroxybiphenyl was not only incorporated into aucuparin but also into the dibenzofuran eriobofuran, the accumulation of which paralleled that of aucuparin. However, biphenyl 2'-hydroxylase activity proposed to be involved in dibenzofuran formation was detected in neither microsomes nor cell-free extracts in the presence of NADPH and 2-oxoglutarate, respectively. Nevertheless, a basis for studying biphenyl biosynthesis at the gene level is provided.

Differential effect of elicitors on biphenyl and dibenzofuran formation in Sorbus aucuparia cell cultures.

The Rosaceous subtribe Pyrinae (formerly subfamily Maloideae) is well-known for its economically important fruit trees, such as apple and pear, and also includes Sorbus aucuparia. Elicitor-treated S. aucuparia cell cultures are used to study the biosynthesis of the Pyrinae-specific phytoalexins, biphenyls and dibenzofurans. Three biphenyls (aucuparin, noraucuparin, 2'-hydroxyaucuparin) and a dibenzofuran (eriobofuran) were isolated and structure elucidated using GC-MS and NMR. A second dibenzofuran of low abundance was tentatively assigned as noreriobofuran. Treatment of S. aucuparia cell cultures with yeast extract induced the formation of aucuparin as the major phytoalexin. In contrast, addition of preparations from the fire blight bacterium, Erwinia amylovora, and the scab-causing fungus, Venturia inaequalis, resulted in accumulation of eriobofuran as the major inducible constituent. Methyl jasmonate was a poor elicitor. The observations are suggestive of a biogenic relationship between biphenyls and dibenzofurans. Elicitor-treated S. aucuparia cell cultures provide an interesting in vitro system for studying biphenyl and dibenzofuran metabolism in the economically valuable Pyrinae.

[Spacial structure of epiphytic yeast communities on fruits of Sorbus aucuparia L].

The subject of this research is epiphytic yeast communities that form on the surface of Sorbus aucuparia. The object is to make quantitative assessment of the yeast communities' differentiation of the same but distant substratum. Results of the factor variance nidicolous analysis demonstrated that with increase in distances, there are increases in the variation of total number and relative abundance of the dominant yeast communities. The average similarity between groups of single fruits (Sorensen's Quotient of Similarity) regularly decreased with distance. The results demonstrate that the number and structure of separate yeast groups depend not only on ecological factors but also on proximity to other communities. Such aggregation in the distribution of the microorganisms' species caused by migration and colonial resettlement should be taken into account when analyzing their diversity in natural habitats.

Diversity of predominant endophytic bacteria in European deciduous and coniferous trees.

The diversity of endophytic bacteria residing in root, stem, and leaf tissues was examined in coniferous and deciduous tree species, Scots pine (Pinus sylvestris L.), silver birch (Betula pendula Roth), and rowan (Sorbus aucuparia L.). Using cultivation-dependent and -independent analyses, the bacterial communities were observed to be significantly different in the belowground (roots and rhizosphere) and aboveground (leaves and stems) samples of the respective host trees. No significant differences, with respect to the different tree species, were observed in the associated communities. Predominant cultivable endophytes isolated included bacteria closely related to Bacillus subtilis, Bacillus licheniformis, Paenibacillus spp., and Acinetobacter calcoaceticus. Comparisons of the most abundant cultivable bacteria in the rhizosphere and root samples suggested that root endophytic bacteria may be in residence through processes of selection or active colonization rather than by passive diffusion from the rhizosphere.

Mycological flora on tree fruits, crust, leaves and pollen Sorbus domestica L.

Plant-microbial interactive relations with respect to determine mycoflora of the Sorbus domestica L.--fruits, crust, leaves and pollen were studied in 2 Slovak regions. On the fruit samples the genera Alternaria, Botrytis, Cladosporium, Mucor and Penicillium occurred, on the leaves the genera Alternaria, Cladosporium and Penicillium prevailed and on crust the genera Alternaria, Cladosporium, Penicillium and Trichoderma appeared to be dominant, respectively. Isolates from the Sorbus domestica L. fruits were present by 11 genera and 13 species of microscopic fungi and isolates from pollen such as Alternaria, Botrytis, Cladosporium, Penicillium, Mycelia, Mucor and Trichoderma appeared to be the most frequently occurring genera. On the basis of further taxonomic determination, from the genera Aspergillus were isolated and identified representatives of species A. clavatus, A. fumigatus, A. niger, A. ochraceus, A. terreus. It is necessary to point out that the isolated genera Aspergillus and Penicillium are considered as the most important producers of mycotoxins.

Notes on a plant parasite fungus in Portugal: Gymnosporangium cornutum

A rust fungus identified as Gymnosporangium cornutum was found on Sorbus aucuparia in Serra da Estrela (Manteigas), and the disease was severe at that location. Despite the abundance and worldwide occurrence of the genus Gymnosporangium, studies in Portugal are still limited(AU)

Notes on a plant parasite fungus in Portugal: Gymnosporangium cornutum.

A rust fungus identified as Gymnosporangium cornutum was found on Sorbus aucuparia in Serra da Estrela (Manteigas), and the disease was severe at that location. Despite the abundance and worldwide occurrence of the genus Gymnosporangium, studies in Portugal are still limited.

Mycological survey of ripped service tree fruits (Sorbus domestica L.) with an emphasis on toxinogenic fungi.

To investigate a possible incidence of microscopic fungi in ripped service tree (Sorbus domestica L.) fruits, a mycological survey was carried out during October-November 2003 in Slovakia. This rare kind of fruit is renowned for its significant curative actions in various human and animal diseases. The study revealed that all 24 surface sterilized fruits analysed were contaminated with fungi. The most dominant endogenous contaminant encountered was Cladosporium cladosporioides (Fres.) de Vries followed by Alternaria alternata (Fr.) Keissler and Penicillium expansum Link with 88%, 63% and 54% frequency, respectively. Furthermore, 24 other fungal species were associated with the fruits as well. P. expansum (40), P. carneum (Frisvad) Frisvad/Penicillium paneum Frisvad (35) and P. griseofulvum Dierckx (6) isolates recovered from the fruits were screened by an agar plug method for production of mycotoxin patulin, all with positive results. In addition, citrinin, griseofulvin and zearalenon production by appropriate species isolates were detected. Despite of a limited number of samples of the service tree fruits examined during this study, it was concluded that the ripening of service tree fruits is accompanied with the presence of typical rotting-fungi as well as of some others, which have not previously been reported in connection with fruit. Furthermore, it was suggested that the ripped service tree fruits should be considered as a potential source of significant fungal secondary metabolites including mycotoxins. Secondary metabolite profiles of the species identified during the study were included here.