Investigating the recovery phenotype phenomenon in Aster Yellows-infected Grapevine

Van der Vyver, Ane (2017-12)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: South Africa is ranked as the seventh largest wine producing country in the world. Grapevine is one of the most important crops, which warrants extensive research on pathogens and diseases that impact vine health. Aster Yellows (AY) phytoplasma was first identified in South African vineyards in 2010, and poses a major threat to local vineyards. The pathogen symptomatology results in substantial grape yield loss and in many cases death. Though no treatment for AY-infections have been commercialised, a common practice among farmers have been to inflict physiological and chemical stresses on infected plants resulting in the induction of a recovery phenotype. It is unknown whether this recovery is permanent. The aim of this study was to identify an AY-infected vineyard and induce a recovery in half of the sample group, after which the AY-infection status of the plants was monitored over two years. Furthermore, the AY genetic diversity of isolates in the vineyard were investigated to ensure that any observed recovery is not due to false negative diagnostics. The effect of possible viral pathogens on recovery phenotype induction in AY-infected vines was also investigated. A triple-nested PCR assay allowed for the identification of 40 AY-infected and 40 healthy plants in February 2016, after which half of each experimental group was coppiced to induce a recovery phenotype. A large-scale remission in AY-infection was observed throughout the vineyard, both in coppiced and uncoppiced plants. Through RFLP assays and Sanger sequencing, a single genetic variant was observed in the studied vineyard, thereby suggesting that the observed recovery was a true one. Grapevine viruses were found in almost all of the AY-positive plants before coppicing, with all healthy plants being virus free. This changed after coppicing however, where a large remission in virus infections was seen post coppicing in AY-positive plants. Additionally, viruses were identified in a small number of AY-negative plants after coppicing. The presence of viruses seemed to have no effect on recovery phenotype induction. This study contributes to our understanding of recovery phenotype induction, reporting a large-scale remission of the pathogen even in the absence of coppicing.

AFRIKAANSE OPSOMMING: Suid-Afrika word as die sewende grootste wynproduserende land in die wêreld beskou. Druiwe wingerdstokke is een van die belangrikste gewasse, wat navorsing oor wingerdpatogene en -siektes dus sterk motiveer. Die voorkoms van Astervergeeling (AY) fitoplasma is vir die eerste keer in 2010 in Suid-Afrika aan geteken en is ‘n groot bedreiging tot plaaslike wingerde. Simptome van die patogeen sluit in aanslienlike opbrengsverlies en in baie gevalle terugsterf van plante. Alhoewel geen kommersiële chemiese behandelings vir AY-infeksies beskikbaar is nie, is ‘n algemene praktyk onder boere om fisiologiese of chemiese stresse toe te pas op siek plante, wat lei tot die induksie van ‘n herstellings-fenotipe (RP). Dit is tans onbekend of hierdie herstelling permanent is. Die doel van hierdie projek was om ‘n AY-geïnfekteerde wingerd te identifiseer en ‘n RP in die helfde van die eksperimentele groep te bewerkstellig, waarna die AY infeksiestatus oor twee jaar gemonitor is. Verder is die AY genetiese diversiteit binne die wingerd ook ondersoek om te verseker dat enige waargenome herstelling nie te wyte is aan vals negatiewe diagnoses nie. Die moontlike effek van virus patogene op die RP indusering in AY-besmette wingerdstokke is ook ondersoek. ‘n Drievoudige PKR toets is gebruik vir die identifisering van 40 AY-positiewe en 40 gesonde plante in Februarie 2016, waarna die helfde van elke groep net bo die entlas afgesny is om ‘n RP te induseer. ‘n Grootskaalse remissie in AY-infeksie was waargeneem, beide in afgesnyde en ongesnyde plante. Beperkingsfragmentlengte Polimorfisme-toetse en Sanger-volgordebepaling het bevestig dat ‘n enkelle genetiese variant in die wingerd voorgekom het, wat vals negatiewe diagnoses elimineer het, en dus daarop dui dat die waargenome RP 'n ware een was. Virusse is gevind in byna al die AY-positiewe plante voor die afsny van die plante, terwyl alle gesonde plante virus-vry was. ‘n Remissie in virus infeksies in AY-positiewe plante na afsny het voorgekom. Daarbenewens is virusse in ‘n klein aantal AY-negatiewe plante geïdentifiseer na afsny. Hierdie studie dra by tot ons kennis van RP-indusering deurdat ‘n grootskaalse remissie in die voorkoms van die patogeen waargeneem was, ongeag van of plante afgesny was of nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102893
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