The incidence and distribution of grapevine yellows disease in South African vineyards

Carstens, Roleen (2014-04)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: South Africa is ranked eighth in the world as far as international wine production is concerned and in terms of area under bearing vines South Africa is ranked 12th. In 2011 the wine industry contributed R4 204.4 million to the South African economy in state revenue from wine products. The importance of viticulture to the economy of South Africa forces the industry to limit the effect of all disease causing pathogens in order to keep their competitive edge. Aster yellows (AY) phytoplasma 16SrI-B subgroup was reported for the first time in grapevine (Vitis vinifera L. (Vitaceae)) in South Africa in 2006. Worldwide phytoplasma diseases of grapevine cause serious damage ranging from lower yields to the death of vines. The lack of knowledge about the epidemiology of AY disease makes it difficult to determine the impact of the disease on the South African wine industry. The aim of this study was to conduct surveys in disease-affected vineyards in the Vredendal region to determine the incidence and spatial distribution of the disease in a variety of cultivars. The field surveys based on visual symptoms of AY disease were confirmed by polymerase chain reaction (PCR). A survey was also conducted in and around AY-infected vineyards in search of possible alternative host plants of the phytoplasma. Spatial distribution of AY-affected vines were analysed using the PATCHY spatial analysis package. A rapid decline of AY-affected Chardonnay eventually leading to the death of vines was observed, confirming the sensitivity of Chardonnay towards grapevine yellows infections. Symptomless AY infections occurred and AY could not be detected in all symptomatic vines, which indicate uneven distribution of AY in individual vines. Molecular analyses using PCR-RFLP showed that all vines sampled in the Vredendal vicinity contained AY phytoplasma only. No phytoplasmas were present in any weeds or other possible host plants tested. Although the mean yearly disease incidences of Chardonnay (29.95%) and Chenin blanc (16.64%) were higher than Pinotage (5.80%) over the four-year survey period, there was no statistically significant difference between the disease incidences of these three cultivars. The mean yearly disease incidence showed a trend over time and the disease incidence of the first year was significantly lower than that of the other years. Chardonnay showed a cumulative disease incidence of 37.77% at the end of the 4-year study which means that Chardonnay vineyards can be 100% AY infected in ten years’ time. Spatial distribution patterns of AY-infected vines were mostly non-random with clustering of disease affected vines along and across vine rows. With the exception of one vineyard, aggregation of AY-affected vines mostly occurred on the edge of vineyards adjacent to infected vineyards. This epidemiological study gives an indication of the sensitivity of the different cultivars towards AY, the tempo of spreading and the future impact of the disease on the South African wine industry. It also contributes valuable information towards the development of a management strategy for grapevine yellows disease in South African vineyards.

AFRIKAANSE OPSOMMING: Suid- Afrika is op agtste op die wêreld ranglys wat internasionale produksie van wyn aan betref, en in terme van oppervlakte onder wingerd, is Suid-Afrika 12de. In 2011 het die wynbedryf R4 204.4 miljoen tot die Suid-Afrikaanse ekonomie bygedra in staats inkomste uit wyn produkte. Die belangrikheid van wingerd tot die ekonomie van Suid-Afrika dwing die bedryf om die effek van alle siekteveroorsakende patogene te beperk, om sodoende hul kompeterende voordeel te behou. Aster vergeling (AY) fitoplasma 16SrI-B subgroep is vir die eerste keer in 2006 in wingerd (Vitis vinifera L. (Vitaceae)) in Suid-Afrika waargeneem. Fitoplasma siektes van wingerd veroorsaak wêreldwyd ernstige skade wat wissel van laer opbrengste tot die afsterf van wingerdstokke. Die gebrek aan kennis oor die epidemiologie van astervergeling siekte maak dit moeilik om die impak van die siekte op die Suid-Afrikaanse wynbedryf te bepaal. Die doel van hierdie studie was om ‘n opname te maak in siekte geaffekteerde wingerde in die Vredendal omgewing om sodoende siekte voorkoms en verspreidingspatrone van die siekte in 'n verskeidenheid van kultivars te bepaal. Die veld opnames, gebaseer op visuele simptome van aster vergeling siekte, was bevestig deur polimerase kettingreaksie (PKR). ‘n Opname is ook in en om aster vergeling geaffekteerde wingerde uitgevoer, op soek na moontlike alternatiewe gasheer plante van die fitoplasma. Verspreidingspatrone van astervergeling geaffekteerde wingerde is ontleed met behulp van die PATCHY ruimtelike analise pakket. 'n Vinnige agteruitgang van AY geaffekteerde Chardonnay, wat uiteindelik gelei het tot die afsterf van wingerde, is waargeneem, wat die sensitiwiteit van Chardonnay teenoor wingerdvergeling infeksie bevestig. Simptoomlose astervergeling fitoplasma infeksies kom voor en astervergeling fitoplasma kon nie opgespoor word in alle simptomatiese wingerdstokke nie, wat op oneweredige verspreiding van AY fitoplasma in individuele wingerdstokke dui. Molekulêre ontledings met behulp van PKR-RFLP het getoon dat alle wingerdstokke, wat in die Vredendal omgewing getoets is, slegs astervergeling fitoplasma bevat. Geen fitoplasmas was teenwoordig in enige onkruide of ander moontlike gasheer plante. Hoewel die gemiddelde jaarlikse siekte voorkoms van Chardonnay (29,95%) en Chenin Blanc (16,64%) oor die vier-jaar opname periode hoër was as dié van Pinotage (5,80%), was daar geen statisties beduidende verskil tussen die siekte voorkoms van hierdie drie kultivars nie. Die gemiddelde jaarlikse siekte voorkoms het 'n tendens oor tyd getoon, en die siekte voorkoms van die eerste jaar was betekenisvol laer as dié van die ander jare. Chardonnay het ‘n kumulatiewe siekte voorkoms van 37.77% aan die einde van die 4-jaar studie getoon, wat beteken dat Chardonnay wingerde binne 10 jaar 100% besmet kan wees met AY. Verspreidingspatrone van AY geaffekteerde wingerdstokke was meestal nie-ewekansig met bondeling van geaffekteerde wingerdstokke in en oor wingerd rye. Bondeling van AY geaffekteerde wingerdstokke het, met die uitsondering van een wingerd, meestal op die kant van wingerde aanliggend aan besmette wingerde, voorgekom. Die epidemiologiese studie gee 'n aanduiding van die sensitiwiteit van die verskillende kultivars ten opsigte van AY, die tempo van die verspreiding en die toekomstige impak van die siekte op die Suid-Afrikaanse wynbedryf. Dit dra ook waardevolle inligting by tot die ontwikkeling van 'n strategie vir die bestuur van wingerdvergeling siekte in Suid-Afrikaanse wingerde.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86683
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