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

[摘要] ENGLISH ABSTRACT: South Africa is ranked eighth in the world as far as international wine production isconcerned and in terms of area under bearing vines South Africa is ranked 12th. In 2011the wine industry contributed R4 204.4 million to the South African economy in staterevenue from wine products. The importance of viticulture to the economy of South Africaforces the industry to limit the effect of all disease causing pathogens in order to keep theircompetitive edge. Aster yellows (AY) phytoplasma 16SrI-B subgroup was reported for thefirst time in grapevine (Vitis vinifera L. (Vitaceae)) in South Africa in 2006. Worldwidephytoplasma diseases of grapevine cause serious damage ranging from lower yields tothe death of vines. The lack of knowledge about the epidemiology of AY disease makes itdifficult 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 theVredendal region to determine the incidence and spatial distribution of the disease in avariety of cultivars. The field surveys based on visual symptoms of AY disease wereconfirmed by polymerase chain reaction (PCR). A survey was also conducted in andaround AY-infected vineyards in search of possible alternative host plants of thephytoplasma. Spatial distribution of AY-affected vines were analysed using the PATCHYspatial analysis package.A rapid decline of AY-affected Chardonnay eventually leading to the death of vines wasobserved, confirming the sensitivity of Chardonnay towards grapevine yellows infections.Symptomless AY infections occurred and AY could not be detected in all symptomaticvines, which indicate uneven distribution of AY in individual vines. Molecular analysesusing PCR-RFLP showed that all vines sampled in the Vredendal vicinity contained AYphytoplasma only. No phytoplasmas were present in any weeds or other possible hostplants 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 threecultivars. The mean yearly disease incidence showed a trend over time and the diseaseincidence of the first year was significantly lower than that of the other years. Chardonnayshowed a cumulative disease incidence of 37.77% at the end of the 4-year study whichmeans that Chardonnay vineyards can be 100% AY infected in ten years' time. Spatialdistribution patterns of AY-infected vines were mostly non-random with clustering ofdisease 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 toinfected vineyards.This epidemiological study gives an indication of the sensitivity of the different cultivarstowards AY, the tempo of spreading and the future impact of the disease on the SouthAfrican wine industry. It also contributes valuable information towards the development ofa management strategy for grapevine yellows disease in South African vineyards.

[发布机构] Stellenbosch University