Investigating the recovery phenotype phenomenon in Aster Yellows-infected Grapevine

[摘要] 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.

[发布机构] Stellenbosch University