Genetic diversity and identification of putative recombination events in Grapevine rupestris stem pitting-associated virus

Mostert, Ilani (2017-12)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Phylogenetic analysis for variant classification plays a key role in the characterisation of the aetiological role of viruses. The genomic regions selected to identify viral variants and the occurrence of recombination has the potential to influence tree topologies. To investigate the impact of these factors on variant classification, and to evaluate the success of certification schemes in eliminating virus infection, a diversity study was performed on Grapevine rupestris stem pitting-associated virus (GRSPaV), a ubiquitous virus commonly detected in cultivated vines and reportedly associated with Rupestris Stem Pitting disorder. Three surveys were conducted to characterise and compare the genetic diversity of GRSPaV on a global and local level, using a phylogenetic approach. The first constituted a collection of accessions from various countries to represent global virus diversity. A second survey was carried out on local mother blocks that previously conformed to certification requirements for South Africa. Finally, GRSPaV diversity in South African vineyards established prior to the implementation of current sanitary protocols was investigated. Two genomic areas, the coat protein and replicase domains, were selected for this study as these were used to characterise the sequence diversity of GRSPaV in previous studies. Mixed infections were found to occur within single vines, the genetic diversity of GRSPaV was confirmed with the clustering of sequences into five of the six distinct, currently recognised lineages, and a seventh, previously unclassified lineage was detected. Furthermore, the ability of the two domains to detect and classify variants was compared. Additional evidence for recombination in GRSPaV was provided and a correlation between recombinant sequences and inconsistencies between topologies generated by the two genome regions, was observed. Results indicate that disease control methods were moderately successful, but less effective at eliminating non-symptomatic variants. The study illustrates the effect of recombination on phylogenetic trees, and emphasises the importance of accounting for such factors in the characterisation of virus diversity. Increased knowledge of the recombination events within the GRSPaV genome could promote the development of a standardised method for variant classification and the clarification of the aetiological role of the virus.

AFRIKAANSE OPSOMMING: Filogenetiese analise vir variantklassifikasie is belangrik vir die karakterisering van die etiologiese rol van virusse. Die genomiese areas wat gebruik word om virale variante te identifiseer tesame met die verskynsel van rekombinasie het die potensiaal om boomtopologieë te beïnvloed. Om die impak van hierdie faktore op variantklassifikasie te ondersoek, en om die sukses van sertifiseringskemas in die eliminasie van virusinfeksie te evalueer, is ‘n diversiteitstudie uitgevoer op “Grapevine rupestris stem pitting-associated virus” (GRSPaV), ‘n algemene virus wat gereeld in gekweekte wingerde opgespoor word en verbind is met Rupestris-stamverpitting. Drie opnames is uitgevoer om die genetiese diversiteit van GRSPaV op ‘n globale en plaaslike vlak te karakteriseer en te vergelyk deur ‘n filogenetiese benadering. Die eerste bestaan uit ‘n versameling inskrywings uit verskeie lande om globale virusdiversiteit te verteenwoordig. ‘n Tweede opname is uitgevoer op plaaslike moederblokke wat voorheen aan Suid-Afrikaanse sertifiseringsvereistes voldoen het. Laastens is GRSPaV diversiteit in Suid-Afrikaanse wingerde wat voor die implementering van huidige sanitêre protokolle gevestig is, ondersoek. Twee genomiese areas, die kapsiedproteïen- en die replikasedomein, is geselekteer vir hierdie studie aangesien beide voorheen gebruik is om die nukleotiedvolgordediversiteit van GRSPaV in vorige studies te karakteriseer. Infeksies van meer as een variant is in enkele wingerdstokke gevind. Die genetiese diversiteit van GRSPaV is bevestig met die groepering van nukleotiedvolgordes in vyf van die ses afsonderlike variantgroepe wat tans in literatuur erken word, en ‘n sewende, voorheen ongeklassifiseerde groep is opgespoor. Verder is die vermoë van die twee domeine om variante op te spoor en te klassifiseer, vergelyk. Addisionele bewyse vir rekombinasie in GRSPaV is gelewer, en ‘n korrelasie tussen rekombinante isolate en onreëlmatighede tussen topologieë wat deur die twee genoomareas gegenereer is, is waargeneem. Resultate dui daarop dat metodes om infeksies te beheer matig suksesvol was, maar minder doeltreffend om niesimptomatiese variante uit te skakel. Die studie illustreer die effek van rekombinasie op filogenetiese bome, en beklemtoon die belangrikheid daarvan om sulke faktore in ag te neem tydens die karakterisering van virusdiversiteit. Uitgebreide kennis van die rekombinasiegebeure in die GRSPaV genoom kan die ontwikkeling van ‘n gestandaardiseerde metode vir variantklassifikasie bevorder, en help om die etiologiese rol van die virus op te klaar.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102924
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