The determination of the spatial and temporal distribution of Aster Yellows phytoplasma in grapevine

[摘要] ENGLISH ABSTRACT: South Africa is ranked amongst the top ten for wine production internationally. Viticulturecontributes immensely to the economy, which justifies research into the pathogens that maynegatively affect wine production. Aster Yellows phytoplasma was reported in South Africanvineyards in 2010 and has since been an ongoing problem for grape farmers in affected areas.Throughout the world, phytoplasma diseases such as Grapevine Yellows have causeddetrimental effects on the vines, often resulting in death. The limited knowledge onprevention and control of the pathogen can be attributed to the lack of full understanding ofthe epidemiology and accurate diagnosis.The aim of this study was to determine the spatial distribution of Aster Yellows phytoplasmain individual grapevines and to record a possible temporal or seasonal distribution. Therecovery phenotype phenomenon was encountered during the study and surveys wereconducted in order to determine whether recovery was permanent. In order to perform thestudies, a reliable assay to accurately detect the pathogen in grapevines was required.A comparison between three assays was completed in furtherance of deciding which to usefor the further experimentation. The three assays included a nested PCR utilizing universalprimers, a Real-Time PCR using Syto9 as a double stranded DNA specific dye and a Real-Time PCR with a TaqMan® probe using an identical dilution series. Of the three assaystested, the nested PCR proved to be the most sensitive diagnostic procedure, detecting AsterYellows phytoplasma in very low titers and was thus used for diagnostics in furtherexperiments. In order to determine the spatial patterns of Aster yellows phytoplasmainfection, leaf, petiole, trunk, root and cane samples were taken from three whole grapevineplants. Phloem scrapings obtained from the cane samples yielded more positive results incomparison to the other parts of the plant tested. Not only do phytoplasmas display an erraticspatial distribution, but also have a tendency to change over time. Thirty symptomaticgrapevines were sampled over one and a half growing seasons, with results concluding thatFebruary yielded the most positive diagnoses. Fifty plants that had been previously prunedback and no longer displayed symptoms were also sampled in 2013 and 2014, and all yieldednegative results over both years. This study contributes to comprehension of Aster Yellowsphytoplasma epidemiology and ultimately the advancement of accurate diagnosis.

[发布机构] Stellenbosch University