The suppressive effect of a commercial extract from Durvillaea potatorum and Ascophyllum nodosum on infection of broccoli by Plasmodiophora brassicae.

A sand solution technique demonstrated the capacity for a commercial seaweed extract from Durvillaea potatorum and Ascophyllum nodosum (Seasol Commercial®) to significantly suppress infection of broccoli by Plasmodiophora brassicae. In the primary stages of infection, the extract reduced the number of plasmodia formed in the root hairs by 55 %. Later, in the secondary stages of infection, the extract reduced plasmodia in the root cortical cells by up to 84 %. The suppression of infection was found to be independent of the dilution of the extract applied (1:25 and 1:500). The basis for these results is unlikely to be a nutrient or pH effect since the extract had little impact on these parameters, particularly at the lower dilution (1:200). Rather, we hypothesise that the suppression of infection by the seaweed extract was due to its stimulation of resistance mechanisms in the host, which is possibly related to laminarins in the extract and/or the effect of exogenous growth regulators or undiscovered molecules in the extract disrupting the infection process.

Genera of diaporthalean coelomycetes associated with leaf spots of tree hosts.

Four different genera of diaporthalean coelomycetous fungi associated with leaf spots of tree hosts are morphologically treated and phylogenetically compared based on the DNA sequence data of the large subunit nuclear ribosomal DNA gene (LSU) and the internal transcribed spacers and 5.8S rRNA gene of the nrDNA operon. These include two new Australian genera, namely Auratiopycnidiella, proposed for a leaf spotting fungus occurring on Tristaniopsis laurina in New South Wales, and Disculoides, proposed for two species occurring on leaf spots of Eucalyptus leaves in Victoria. Two new species are described in Aurantiosacculus, a hitherto monotypic genus associated with leaf spots of Eucalyptus in Australia, namely A. acutatus on E. viminalis, and A. eucalyptorum on E. globulus, both occurring in Tasmania. Lastly, an epitype specimen is designated for Erythrogloeum hymenaeae, the type species of the genus Erythrogloeum, and causal agent of a prominent leaf spot disease on Hymenaea courbaril in South America. All four genera are shown to be allied to Diaporthales, although only Aurantiosacculus (Cryphonectriaceae) could be resolved to family level, the rest being incertae sedis.

Fungal Planet description sheets: 69-91.

Novel species of microfungi described in the present study include the following from Australia: Bagadiella victoriae and Bagadiella koalae on Eucalyptus spp., Catenulostroma eucalyptorum on Eucalyptus laevopinea, Cercospora eremochloae on Eremochloa bimaculata, Devriesia queenslandica on Scaevola taccada, Diaporthe musigena on Musa sp., Diaporthe acaciigena on Acacia retinodes, Leptoxyphium kurandae on Eucalyptus sp., Neofusicoccum grevilleae on Grevillea aurea, Phytophthora fluvialis from water in native bushland, Pseudocercospora cyathicola on Cyathea australis, and Teratosphaeria mareebensis on Eucalyptus sp. Other species include Passalora leptophlebiae on Eucalyptus leptophlebia (Brazil), Exophiala tremulae on Populus tremuloides and Dictyosporium stellatum from submerged wood (Canada), Mycosphaerella valgourgensis on Yucca sp. (France), Sclerostagonospora cycadis on Cycas revoluta (Japan), Rachicladosporium pini on Pinus monophylla (Netherlands), Mycosphaerella wachendorfiae on Wachendorfia thyrsifolia and Diaporthe rhusicola on Rhus pendulina (South Africa). Novel genera of hyphomycetes include Noosia banksiae on Banksia aemula (Australia), Utrechtiana cibiessia on Phragmites australis (Netherlands), and Funbolia dimorpha on blackened stem bark of an unidentified tree (USA). Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.

Specific Polymerase Chain Reaction Primers for the Detection of Plasmodiophora brassicae in Soil and Water.

ABSTRACT The development of specific oligonucleotide primers for Plasmodiophora brassicae has led to a nested polymerase chain reaction (PCR) detection method for P. brassicae in soil and water. Initially, the PCR was used to amplify a section of the rDNA repeat. The PCR products were sequenced and the data used to design primers that were directed at the ribosomal RNA genes and internal transcribed spacer regions. Specificity was tested against more than 40 common soil organisms, host plants, and spore suspension contaminants, as well as P. brassicae isolates from around Australia and the world. Sensitivity was determined to be 0.1 fentograms (fg; 10(-15) g) for pure template and as low as 1,000 spores per g of potting mix. In soil, P. brassicae was detected in all soils where the inoculum was sufficient to result in clubroot symptoms. Also outlined is a simple method of DNA extraction from soil.