Browsing by Author "Fischer, Michael"

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    Hymenochaetales associated with esca-related wood rots on grapevine with a special emphasis on the status of esca in South African vineyards
    (Firenze University Press, 2015) Cloete, Mia; Fischer, Michael; Mostert, Lizel; Halleen, Francois
    Esca disease is a problem on grapevines worldwide. This disease complex is characterised by several external and internal symptoms including foliar tiger-stripe chlorosis and necrosis, dieback, wood necrosis and white rot. The causal organisms of esca are primarily Phaeomoniella chlamydospora, several Phaeoacremonium species and basidiomycete species from the order Hymenochaetales, the latter ones responsible for causing the white rot symptom. Basidiomycete species causing the wood rot symptom of esca differ among grapevine-growing areas worldwide. South African vineyards are unique in having a minimum of ten different basidiomycete taxa from five different genera associated with the esca complex. In general, Hymenochaetales species are associated with white rot on woody plants and there are several species that are economically important to the agricultural and forestry industries. Few Hymenochaetales species have been described from the African continent, though this review is an indication of the previously unknown diversity of these fungi in Southern Africa.
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    Pathogenicity of South African Hymenochaetales taxa isolated from esca-infected grapevines
    (Firenze University Press, 2015) Cloete, Mia; Mostert, Lizel; Fischer, Michael; Halleen, Francois
    Little is known about the pathogenicity and etiology of Hymenochaetales taxa associated with esca in South Africa. Ten South African Hymenochaetales taxa associated with esca in grapevine were subjected to basic enzyme assays to determine which ligninolytic enzymes were secreted by each taxon. In addition, a field trial was undertaken to determine the pathogenicity of these taxa. Twenty-seven fungal isolates and two negative controls were inoculated into wounds made on mature grapevines of the cultivars Shiraz and Mourvédre. Inoculated vines were evaluated for white rot symptoms after 24 months. The results of the enzyme assays indicated a difference in enzyme secretion among taxa and also between isolates of the same taxa. All isolates secreted cellulase and laccase, but there was a difference in isolates’ ability to secrete manganese peroxidase and lignin peroxidase. The results of the pathogenicity trial showed that all of the isolates used were capable of causing the characteristic white rot symptom in the wood. There were clear differences in susceptibility to white rot between the two cultivars tested, namely Shiraz and Mourvédre. The cultivars also differed in which taxa proved to be more virulent. On Shiraz a specific isolate of Taxon 6 (an Inonotus sp.), Phellinus sp. and Inonotus setuloso-croceus were significantly virulent. On Mourvédre, Taxon 3 (an Inocutis sp.) was significantly virulent.