Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: South Africa is ranked amongst the top ten for wine production internationally. Viticulture
contributes immensely to the economy, which justifies research into the pathogens that may
negatively affect wine production. Aster Yellows phytoplasma was reported in South African
vineyards 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 caused
detrimental effects on the vines, often resulting in death. The limited knowledge on
prevention and control of the pathogen can be attributed to the lack of full understanding of
the epidemiology and accurate diagnosis.
The aim of this study was to determine the spatial distribution of Aster Yellows phytoplasma
in individual grapevines and to record a possible temporal or seasonal distribution. The
recovery phenotype phenomenon was encountered during the study and surveys were
conducted in order to determine whether recovery was permanent. In order to perform the
studies, 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 use
for the further experimentation. The three assays included a nested PCR utilizing universal
primers, 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 assays
tested, the nested PCR proved to be the most sensitive diagnostic procedure, detecting Aster
Yellows phytoplasma in very low titers and was thus used for diagnostics in further
experiments. In order to determine the spatial patterns of Aster yellows phytoplasma
infection, leaf, petiole, trunk, root and cane samples were taken from three whole grapevine
plants. Phloem scrapings obtained from the cane samples yielded more positive results in
comparison to the other parts of the plant tested. Not only do phytoplasmas display an erratic
spatial distribution, but also have a tendency to change over time. Thirty symptomatic
grapevines were sampled over one and a half growing seasons, with results concluding that
February yielded the most positive diagnoses. Fifty plants that had been previously pruned
back and no longer displayed symptoms were also sampled in 2013 and 2014, and all yielded
negative results over both years. This study contributes to comprehension of Aster Yellows
phytoplasma epidemiology and ultimately the advancement of accurate diagnosis. / AFRIKAANSE OPSOMMING: Suid-Afrika is internasionaal geposisioneer onder die top tien vir die produksie van wyn.
Wingerd dra geweldig by tot die ekonomie, wat navorsing oor die patogene wat
wynporduksie negatief beïnvloed, regverdig. Aster Yellows phytoplasmais in 2010
gerapporteer in Suid-Afrikaanse wingerde en is sedertdien 'n deurlopende probleem vir
druiweboere in geaffekteerde gebiede. Dwarsdeur die wêreld, het fitoplasma siektes soos
Grapevine Yellows ‘n nadelige uitwerking op wingerde, wat dikwels lei tot plantsterftes. Die
beperkte kennis oor die voorkoming en beheer van die patogeen kan toegeskryf word aan die
gebrek aan begrip van die epidemiologie en akkurate diagnose .
Die doel van hierdie studie was om die ruimtelike verspreiding van Aster geel fitoplasma in
individuele wingerdstokke te bepaal en 'n moontlike tydelike of seisoenale verspreiding aan
te teken. Die herstel-fenotipe verskynsel is tydens die studie teëgekom en opnames is
uitgevoer ten einde te bepaal of die herstel permanent was. Ten einde die studie uit te voer , is
'n betroubare toets vereis om die patogeen in wingerde akkuraat te spoor.
: Drie toetse is vergelyk (en geëvalueer) vir hulle geskikthed vir gebruik in die studie. Die
drie toetse het ingesluit 'n geneste PKR wat gebruik maak van universele primers, 'n in-tydse
PKR (real-time PCR) wat Syto9 gebruik as 'n dubbelstring DNS spesifieke kleurstof, en 'n
in-tydse PKR met 'n TaqMan® peiler, en is vergelyk met behulp van 'n identiese vedunnings
reeks. Van die drie toetse , is die geneste PCR bewys om die mees sensitiewe diagnostiese
prosedure te wees , en kon Aster geel fitoplasma in baie lae titers opspoor en is dus gebruik
vir die diagnose in verdere eksperimente. Ten einde die ruimtelike patrone van Aster geel
fitoplasma infeksie te bepaal, is blaar, blaarsteel, stam, wortel en loot monsters van drie volle
wingerdstokke geneem. Floëem skraapsels verkry uit die loot monsters het meer positiewe
resultate opgelewer in vergelyking met die ander dele van die plant. Nie net vertoon
phytoplasmas 'n wisselvallige ruimtelike verspreiding nie, maar het ook 'n neiging om te
verander met verloop van tyd. Dertig simptomaties wingerdstokke is versamel oor een en 'n
half groeiseisoene,en die resultate het gewys dat Februarie die meeste positiewe diagnoses
het. Monsters is versamel in 2013 en 2014 van vyftig plante wat voorheen teruggesnoei is en
nie meer simptome vertoon nie, en alle monsters het negatiewe resultate opgelewer oor beide
jare. Hierdie studie dra by tot begrip van Aster geel fitoplasma epidemiologie en uiteindelik
die bevordering van akkurate diagnose.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96990 |
| Date | 04 1900 |
| Creators | Smyth, Natalie |
| Contributors | Burger, Johan T., Souza Richards, Rosineide, Stellenbosch University. Faculty of Agrisciences. Dept. of Genetics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 78 pages : illustrations |
| Rights | Stellenbosch University |
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