The characterization of the basidiomycetes and other fungi associated with esca of grapevines in South Africa

[摘要] ENGLISH ABSTRACT: Esca is a disease affecting grapevines and is potentially devastating as there are economiclosses due to a decrease in yield, wine quality and berry quality. Vineyards also need to bereplaced earlier and therefore esca has a great impact on the wine, table grape and raisinindustries. The disease is known to affect vineyards worldwide and has been studiedextensively in Europe, but not in South Africa. Esca diseased grapevines were observed forthe first time prior to 1981 in South African vineyards. The disease is primarily caused byPhaeoacremonium aleophilum, Phaeomoniella chlamydospora (both causing brown andblack wood streaking) and white rot basidiomycete species such as Fomitiporia mediterraneawhich cause wood rot in the trunks and arms of generally older grapevines. Species of theBotryosphaeriaceae and Phomopsis (mainly Phomopsis viticola) and Eutypa lata have alsobeen isolated from esca diseased vines, but their association with esca is unclear.Some of the symptoms associated with the disease on most grapevine cultivarsinclude 'tiger-stripe' foliar symptoms, apoplexy and berry symptoms such as shriveling,discoloration and 'black measles'. These external symptoms as well as internal symptoms arethought to be a result of toxin and enzyme production by the fungi involved. Symptomexpression is erratic and varies from year to year making investigations into the causal fungiand the toxins and enzymes secreted in planta difficult.Vines with internal or external symptoms of esca were sampled in this study fromtable and wine grape cultivars in 37 towns in the Western Cape, Northern Cape and Limpopoprovinces. The majority of sampled vines were over ten years of age, but vines as young astwo to three years were also found to be infected. The external symptoms included dieback,tiger striped leaves, berry symptoms (shriveling, insufficient colouring and black spots) andapoplexy. These symptoms resembled those found on grapevines in Europe, Australia and theUSA. The internal symptoms found were also similar to European symptoms and includedwhite rot, black and brown wood streaking, brown necrosis within white rot, sectorial brownnecrosis and central brown/ red/ black margin. The fungi mostly isolated from the white rotwere the basidiomycetes. Black and brown wood streaking was primarily caused byPhaeomoniella chlamydospora. Brown necrosis within the white rot was caused byPhaeomoniella chlamydospora and less frequently by Phaeoacremonium spp., Eutypa lata,Botryosphaeriaceae and Pleurostomophora richardsiae. The sectorial brown necrosis and the central/ brown/ red/ black margin were dominated by Phaeomoniella chlamydospora. Thefruiting bodies of the basidiomycetes were found on only a few grapevines.The fungal species associated with the internal wood symptoms were characterized oncultural growth patterns, morphology as well as phylogenetic inference. The gene areassequenced included the internal transcribed spacers and the 5.8S rRNA gene for thebasidiomycetes and Phomopsis isolates, the partial b-tubulin gene for Phaeoacremoniumisolates and the partial translation elongation-1a gene for the Botryosphaeriaceae isolates.The basidiomycete isolates fell into ten taxa within the Hymenochaetales of which two couldbe linked to known genera, namely Fomitiporia and Phellinus. The ten basidiomycete taxa donot correspond to any published sequences. Eutypa lata, Diaporthe ambigua, Diplodiaseriata, Neofusicoccum australe, Neofusicoccum parvum, Phomopsis viticola, Phomopsis sp.1, Phaeomoniella chlamydospora and six species of Phaeoacremonium including P.aleophilum, P. alvesii, P. parasiticum, P. iranianum, P. mortoniae and P. sicilianum werealso isolated of which the latter three are reported for the first time in South Africa.To understand the role of the basidiomycetes in the complex, toxin and enzymeanalyses was determined for these fungi. Selected basidiomycete isolates were grown up inliquid broth and extractions performed to test for the presence of 4-hydroxy-benzaldehyde.All of the basidiomycete isolates were able to produce this toxin which is known to bephytotoxic. The basidiomycetes were then tested for the presence of certain wood degradingenzymes. All of the taxa were able to produce manganese peroxidase. Laccase was producedby all taxa, except Taxon 8. Lignin peroxidase was produced by Taxa 1, 2, 7, Fomitiporia sp.and the Phellinus sp. All the basidiomycete isolates were able to produce cellulose and nonewere able to produce xylanase. These enzyme tests showed that the basidiomycetes produce awide variety of enzymes which are able to degrade cellulase and lignin which are bothstructural components of wood.Given the wide distribution of esca in the grape growing regions investigated in SouthAfrica and the diverse amount of species found, this disease must surely be seen as a limitingfactor to the productive lifespan of vineyards and quality of produce. Preventative measuressuch as sanitation and pruning wound protection contribute to the management of the disease,but many questions still remain about the synergy of the causal fungi, epidemiology andmanagement of esca.

[发布机构] Stellenbosch University