Academic literature on the topic 'Grapevine yellows disease'

A 3-year survey was conducted in Northern Italy to verify the presence and diversity of phytoplasmas in selected vineyards showing symptoms of severe yellows. Symptomatic and asymptomatic grapevines were sampled, and insects were collected using yellow sticky traps. The phytoplasmas detected in grapevine samples were different according to the years: “flavescence dorée” (16SrV-C/D) was detected together with other phytoplasmas such as 16SrXII-A (‘Candidatus Phytoplasma solani’-related, bois noir), 16SrI-B (‘Ca. P. asteris’-related, aster yellows), 16SrX-B (‘Ca. P. prunorum’-related, European stone fruit yellows), and 16SrV-A (‘Ca. P. ulmi’-related, elm yellows). Moreover, phytoplasmas belonging to 16SrVII-A (‘Ca. P. fraxini’-related) and 16SrVI (‘Ca. P. trifolii’-related) subgroups were also identified. Identification of phytoplasmas was also carried out from insects and showed the presence of some of these phytoplasmas in Scaphoideus titanus and Orientus ishidae: 16SrXII-A, 16SrVII, and 16SrVI phytoplasmas were detected in specimens of both species, while 16SrXII-A and 16SrI-B phytoplasma strains were identified in Orientus ishidae and Hyalesthes obsoletus, and 16SrX-B in S. titanus. Direct sequencing of selected amplicons obtained from 16S rRNA, rp, and tuf genes from grapevine and insect samples confirmed the phytoplasma identification. The 16SrVII-A and 16SrVI phytoplasmas were never detected before in grapevine, S. titanus and Orientus ishidae in Europe and their epidemiological importance is being monitored.

An extensive survey was performed from 2002 to 2006 to detect and identify phytoplasmas associated with Chilean grapevines. Nested polymerase chain reaction assays using phytoplasma universal primer pairs P1/P7 and R16F2n/R2 detected phytoplasmas in 34 out of the 94 samples tested (36%). Restriction fragment length polymorphism (RFLP) analyses, cloning, and sequencing allowed identification of phytoplasmas belonging to ribosomal subgroups 16SrI-B, 16SrI-C, 16SrVII-A, and 16SrXII-A. The 16SrVII-A phytoplasma represents a new finding in grapevine; moreover, variability of the RFLP profile was observed in some of the 16SrXII-A phytoplasmas, indicating possible new ribosomal subgroups. Mixed phytoplasma infections and infections of phytoplasmas together with one or more viruses also occurred.

Yellows diseases, caused by phytopathogenic bacteria of the genus Phytoplasma, are a major threat to grapevines worldwide. Because conventional applications against this pathogen are inefficient and disease management is highly challenging, the use of beneficial bacteria has been suggested as a biocontrol solution. A Dyella-like bacterium (DLB), isolated from the Israeli insect vector of grapevine yellows (Hyalesthes obsoletus), was suggested to be an endophyte. To test this hypothesis, the bacterium was introduced by spraying the plant leaves, and it had no apparent phytotoxicity to grapevine. Fluorescent in situ hybridization analysis showed that DLB is colonizing grapevine phloem. Because phytoplasmas inhabit the same niche, DLB interactions with this phytopathogen were examined. When the isolate was introduced to phytoplasma-infected Chardonnay plantlets, morphological disease symptoms were markedly reduced. The mode of DLB action was then tested using bioinformatics and system biology tools. DLB genome analysis suggested that the ability to reduce phytoplasma symptoms is related to inhibition of the pathogenic bacterium. These results provide the first step in examining the potential of DLB as a biological control agent against phytoplasmas in grapevine and, possibly, other agricultural crops.

Grapevine yellows diseases occur in cultivated grapevine (Vitis vinifera L.) on several continents, where the diseases are known by different names depending upon the identities of the causal phytoplasmas. In this study, phytoplasma strains associated with grapevine yellows disease (North American grapevine yellows [NAGY]) in vineyards of Pennsylvania were characterized as belonging to 16S ribosomal RNA (rRNA) gene restriction fragment length polymorphism group 16SrI (aster yellows phytoplasma group), subgroup 16SrI-B (I-B), and variant subgroup I-B*. The strains (NAGYI strains) were subjected to genotyping based on analyses of 16S rRNA and secY genes, and to in silico three-dimensional modeling of the SecY protein. Although the NAGYI strains are closely related to aster yellows (AY) phytoplasma strains and are classified like AY strains in subgroup I-B or in variant subgroup I-B*, the results from genotyping and protein modeling may signal ongoing evolutionary divergence of NAGYI strains from related strains in subgroup 16SrI-B.

Grapevine yellows (GY) are serious phytoplasma-caused diseases affecting viticultural areas worldwide. At present, two principal agents of GY are known to infest grapevines in Germany: Bois noir (BN) and Palatinate grapevine yellows (PGY). Disease management is mostly based on prophylactic measures as there are no curative in-field treatments available. In this context, sensor-based disease detection could be a useful tool for winegrowers. Therefore, hyperspectral imaging (400–2500 nm) was applied to identify phytoplasma-infected greenhouse plants and shoots collected in the field. Disease detection models (Radial-Basis Function Network) have successfully been developed for greenhouse plants of two white grapevine varieties infected with BN and PGY. Differentiation of symptomatic and healthy plants was possible reaching satisfying classification accuracies of up to 96%. However, identification of BN-infected but symptomless vines was difficult and needs further investigation. Regarding shoots collected in the field from different red and white varieties, correct classifications of up to 100% could be reached using a Multi-Layer Perceptron Network for analysis. Thus, hyperspectral imaging seems to be a promising approach for the detection of different GY. Moreover, the 10 most important wavelengths were identified for each disease detection approach, many of which could be found between 400 and 700 nm and in the short-wave infrared region (1585, 2135, and 2300 nm). These wavelengths could be used further to develop multispectral systems.

Grapevine yellows is a destructive, worldwide disease of grapevines that is caused by a phytoplasma, a bacterium-like organism that infects and disrupts the vascular system of shoots. The North American form of grapevine yellows (NAGY) has been observed in New York State since the mid-1970s and in Virginia since the mid-1990s. Symptoms duplicate those of vines suffering from an Australian disease complex known as Australian grapevine yellows (AGY). We sought to determine if infected `Chardonnay' vines have common anatomical characteristics across the three regions. At each geographic site in late summer, 2003–04, leaf and internode samples were taken from younger green regions of shoots and from mature basal regions in the fruiting zone. These were processed for histology. The anatomy of each organ type was compared between locations on the shoot, between geographic locations, and between affected and normal shoots. The phloem was the only tissue universally affected in vines with NAGY or AGY symptoms. In stem internodes, both primary phloem and secondary phloem showed many senescent cells, abnormally proliferated giant cells, and hyperplasia. In affected secondary phloem there was disruption of the radial files of cells that normally differentiate from the cambium into mature phloem cell types. Normal bands of secondary phloem fibers (“hard phloem”) in internodes were weak or absent in affected vines. Leaves also had disrupted phloem organization but near-normal xylem organization in vines with symptoms. Leaves of infected vines frequently showed a disruption of sugar transport out of the leaf blades, manifested by a heavy buildup of starch in chloroplasts of mesophyll cells and bundle-sheath cells.

Abstract This study provides the first data on the occurrence of the mosaic leafhopper Orientus ishidae (Matsumura, 1902) (Hemiptera: Cicadellidae) in Poland. This species is native to Southeast Asia, adventive in Europe and feeds on cultivated plants. Orientus ishidae is a well-known carrier of Grapevine flavescence doree phytoplasma which causes the grapevine yellows disease. Symptoms of phytoplasma diseases of grapevine include deformations, leaf chlorosis and withering of plants. The appearance of this species in Poland might be caused by observed climate variations and insufficient plant health controls in the international trade of plants.

North American grapevine yellows (NAGY) disease has sometimes been attributed to infection of Vitis vinifera L. by Prunus X-disease phytoplasma (‘Candidatus Phytoplasma pruni’) but this attribution may not be fully adequate. In this study, phytoplasma strains related to ‘Ca. Phytoplasma pruni’ were found in NAGY-diseased grapevines in Maryland, Pennsylvania, Virginia, Ohio, Missouri, and New York State. Based on restriction fragment length polymorphism analysis of 16S ribosomal RNA gene (16S rDNA) sequences, the strains (termed NAGYIII strains) were classified in group 16SrIII (X-disease group) but they contained a recognition site for the restriction endonuclease MseI that is not present in the 16S rDNA of ‘Ca. Phytoplasma pruni’. The 16S rDNA of the strains differed by three or four nucleotides from that of ‘Ca. Phytoplasma pruni’, indicating that they belonged to two novel 16S rDNA sequevars, designated NAGYIIIα and NAGYIIIβ. Both sequevars differed from ‘Ca. Phytoplasma pruni’ by a single base in each of three regions corresponding to species-unique (signature) sequences described for ‘Ca. Phytoplasma pruni’. Phylogenetic analyses of 16S rRNA genes and SecY proteins, and single-nucleotide polymorphism analyses of secY and ribosomal protein genes, further distinguished the two grapevine sequevar lineages from one another and from ‘Ca. Phytoplasma pruni’. The NAGYIIIα and NAGYIIIβ sequevars also differed from ‘Ca. Phytoplasma pruni’ in regions of the folded SecY protein that are predicted to be near or exposed at the outer surface of the phytoplasma membrane. No evidence indicated that diseased grapevines contained any phytoplasma strain conforming to ‘Ca. Phytoplasma pruni’ sensu stricto. Because the NAGYIII sequevars have not been reported in X-disease, a question is raised as to whether NAGYIII and Prunus X-disease are caused by different phytoplasma genotypes.

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: South Africa is ranked eighth in the world as far as international wine production is concerned and in terms of area under bearing vines South Africa is ranked 12th. In 2011 the wine industry contributed R4 204.4 million to the South African economy in state revenue from wine products. The importance of viticulture to the economy of South Africa forces the industry to limit the effect of all disease causing pathogens in order to keep their competitive edge. Aster yellows (AY) phytoplasma 16SrI-B subgroup was reported for the first time in grapevine (Vitis vinifera L. (Vitaceae)) in South Africa in 2006. Worldwide phytoplasma diseases of grapevine cause serious damage ranging from lower yields to the death of vines. The lack of knowledge about the epidemiology of AY disease makes it difficult to determine the impact of the disease on the South African wine industry. The aim of this study was to conduct surveys in disease-affected vineyards in the Vredendal region to determine the incidence and spatial distribution of the disease in a variety of cultivars. The field surveys based on visual symptoms of AY disease were confirmed by polymerase chain reaction (PCR). A survey was also conducted in and around AY-infected vineyards in search of possible alternative host plants of the phytoplasma. Spatial distribution of AY-affected vines were analysed using the PATCHY spatial analysis package. A rapid decline of AY-affected Chardonnay eventually leading to the death of vines was observed, confirming the sensitivity of Chardonnay towards grapevine yellows infections. Symptomless AY infections occurred and AY could not be detected in all symptomatic vines, which indicate uneven distribution of AY in individual vines. Molecular analyses using PCR-RFLP showed that all vines sampled in the Vredendal vicinity contained AY phytoplasma only. No phytoplasmas were present in any weeds or other possible host plants tested. Although the mean yearly disease incidences of Chardonnay (29.95%) and Chenin blanc (16.64%) were higher than Pinotage (5.80%) over the four-year survey period, there was no statistically significant difference between the disease incidences of these three cultivars. The mean yearly disease incidence showed a trend over time and the disease incidence of the first year was significantly lower than that of the other years. Chardonnay showed a cumulative disease incidence of 37.77% at the end of the 4-year study which means that Chardonnay vineyards can be 100% AY infected in ten years’ time. Spatial distribution patterns of AY-infected vines were mostly non-random with clustering of disease affected vines along and across vine rows. With the exception of one vineyard, aggregation of AY-affected vines mostly occurred on the edge of vineyards adjacent to infected vineyards. This epidemiological study gives an indication of the sensitivity of the different cultivars towards AY, the tempo of spreading and the future impact of the disease on the South African wine industry. It also contributes valuable information towards the development of a management strategy for grapevine yellows disease in South African vineyards.
AFRIKAANSE OPSOMMING: Suid- Afrika is op agtste op die wêreld ranglys wat internasionale produksie van wyn aan betref, en in terme van oppervlakte onder wingerd, is Suid-Afrika 12de. In 2011 het die wynbedryf R4 204.4 miljoen tot die Suid-Afrikaanse ekonomie bygedra in staats inkomste uit wyn produkte. Die belangrikheid van wingerd tot die ekonomie van Suid-Afrika dwing die bedryf om die effek van alle siekteveroorsakende patogene te beperk, om sodoende hul kompeterende voordeel te behou. Aster vergeling (AY) fitoplasma 16SrI-B subgroep is vir die eerste keer in 2006 in wingerd (Vitis vinifera L. (Vitaceae)) in Suid-Afrika waargeneem. Fitoplasma siektes van wingerd veroorsaak wêreldwyd ernstige skade wat wissel van laer opbrengste tot die afsterf van wingerdstokke. Die gebrek aan kennis oor die epidemiologie van astervergeling siekte maak dit moeilik om die impak van die siekte op die Suid-Afrikaanse wynbedryf te bepaal. Die doel van hierdie studie was om ‘n opname te maak in siekte geaffekteerde wingerde in die Vredendal omgewing om sodoende siekte voorkoms en verspreidingspatrone van die siekte in 'n verskeidenheid van kultivars te bepaal. Die veld opnames, gebaseer op visuele simptome van aster vergeling siekte, was bevestig deur polimerase kettingreaksie (PKR). ‘n Opname is ook in en om aster vergeling geaffekteerde wingerde uitgevoer, op soek na moontlike alternatiewe gasheer plante van die fitoplasma. Verspreidingspatrone van astervergeling geaffekteerde wingerde is ontleed met behulp van die PATCHY ruimtelike analise pakket. 'n Vinnige agteruitgang van AY geaffekteerde Chardonnay, wat uiteindelik gelei het tot die afsterf van wingerde, is waargeneem, wat die sensitiwiteit van Chardonnay teenoor wingerdvergeling infeksie bevestig. Simptoomlose astervergeling fitoplasma infeksies kom voor en astervergeling fitoplasma kon nie opgespoor word in alle simptomatiese wingerdstokke nie, wat op oneweredige verspreiding van AY fitoplasma in individuele wingerdstokke dui. Molekulêre ontledings met behulp van PKR-RFLP het getoon dat alle wingerdstokke, wat in die Vredendal omgewing getoets is, slegs astervergeling fitoplasma bevat. Geen fitoplasmas was teenwoordig in enige onkruide of ander moontlike gasheer plante. Hoewel die gemiddelde jaarlikse siekte voorkoms van Chardonnay (29,95%) en Chenin Blanc (16,64%) oor die vier-jaar opname periode hoër was as dié van Pinotage (5,80%), was daar geen statisties beduidende verskil tussen die siekte voorkoms van hierdie drie kultivars nie. Die gemiddelde jaarlikse siekte voorkoms het 'n tendens oor tyd getoon, en die siekte voorkoms van die eerste jaar was betekenisvol laer as dié van die ander jare. Chardonnay het ‘n kumulatiewe siekte voorkoms van 37.77% aan die einde van die 4-jaar studie getoon, wat beteken dat Chardonnay wingerde binne 10 jaar 100% besmet kan wees met AY. Verspreidingspatrone van AY geaffekteerde wingerdstokke was meestal nie-ewekansig met bondeling van geaffekteerde wingerdstokke in en oor wingerd rye. Bondeling van AY geaffekteerde wingerdstokke het, met die uitsondering van een wingerd, meestal op die kant van wingerde aanliggend aan besmette wingerde, voorgekom. Die epidemiologiese studie gee 'n aanduiding van die sensitiwiteit van die verskillende kultivars ten opsigte van AY, die tempo van die verspreiding en die toekomstige impak van die siekte op die Suid-Afrikaanse wynbedryf. Dit dra ook waardevolle inligting by tot die ontwikkeling van 'n strategie vir die bestuur van wingerdvergeling siekte in Suid-Afrikaanse wingerde.

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.

Os amarelos estão associados a fitoplasmas, procariotos pertencentes à classe Mollicutes que não possuem parede celular e habitam o floema de plantas. Os danos causados pelas doenças de etiologia fitoplasmática são relevantes e podem ocorrer em diversas espécies economicamente importantes. Em videira, pesquisas realizadas em várias partes do mundo têm relatado a presença das doenças do tipo “amarelo”, porém, no Brasil, estas doenças ainda não foram relatadas para esta cultura. Em vinhedos comerciais localizados nos Estados de São Paulo e Paraná têm sido observadas plantas com sintomas semelhantes àqueles provocados por fitoplasmas em outros países. Estes sintomas têm sido caracterizados por amarelecimento e ou avermelhamento foliar, necrose do limbo e rachaduras nas nervuras principais. Com o objetivo de detectar e identificar molecularmente fitoplasmas associados a estes tipos de sintomas, folhas e ramos foram amostrados a partir de plantas sintomática e assintomáticas. A detecção foi conduzida com PCR duplo usando-se os iniciadores R16 mF1/mR2 ou P1/P7 na primeira reação e R16 F2n/R2 na segunda reação. A identificação foi realizada através de PCR duplo com iniciadores específicos e análises de RFLP com as enzimas de restrição AluI, RsaI, KpnI, MseI, HhaI, HpaII, HinfI e MboI. Em 23 plantas amostradas, fitoplasmas foram detectados em 10 delas, através da amplificação do 16S rDNA, visualizado em gel de agarose na forma de bandas de 1,2Kb. A identificação por PCR demonstrou que os fitoplasmas associados ao amarelo da videira pertenciam aos grupos 16SrI e 16SrIII. As análises dos perfis eletroforéticos obtidos com o uso da técnica de RFLP revelaram a presença de fitoplasmas afiliados ao subgrupo 16SrI-B. A constatação de fitoplasmas pertencentes a estes dois grupos nas plantas amostradas demonstraram a ocorrência da doença conhecida como amarelo da videira nos Estados de São Paulo e Paraná. As pesquisas desenvolvidas neste trabalho vêm contribuir para aumentar os conhecimentos sobre o papel e a diversidade dos fitoplasmas no agroecossistema brasileiro.
Yellows diseases are associated with phytoplasmas, wall-less prokaryotes, inhabitant of phloem vessels. Damage caused by these diseases are relevant for some important cultivated botanical species. Grapevine yellows diseases have been observed in several areas of the world, but in Brazil the presence of these diseases had not been reported yet. In vineyards located in São Paulo and Paraná States, plants exhibiting symptoms similar those observed in grapevines from other countries have been observed. The symptoms were characterized by yellowing or redding of leaf blade and ribs, leaf blade necrosis and main ribs fissures. In order to detect and identify phytoplasmas associated with those kind of symptoms, leaves and stems were sampled from symptomatic and asymptomatic plants. The phytoplasma detection was conducted with nested PCR using the primer pairs R16mF1/mR2 or P1/P7 for first reaction and 16 F2n/R2 for second reaction. The identification was carried out by nested PCR with group-specifc primer pairs and RFLP analyses with enzymes AluI, RsaI, KpnI, MseI, HhaI, HpaII, HinfI and MboI. From a total of 23 samples analysed, phytoplasmas were detected in 10 of them, through amplification of the 16S rDNA, visualized through a 1.2Kb band in agarose gel. The identification by PCR demonstrated that phytoplasmas associated with grapevine yellow belong to 16SrI and 16SrIII groups. Analyses of electrophoretic profiles revealed the presence of phytoplasmas affiliated to 16SrI-B subgroup. The presence of phytoplasmas belonging to these two groups in the sampled plants demonstrated the occurrence of yellow disease in grapevine in São Paulo and Paraná States. The investigation conducted in the present work contributed to the knowledgement of the role and the diversity of phytoplasmas in Brasilian ecosystem.

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Phytoplasma diseases have caused disastrous effects in vineyards around the world. Therefore, the recent discovery of phytoplasmas in South African vineyards could be highly detrimental to the local wine industry. Antimicrobial peptides (AMPs) are small molecules expressed by almost all organisms as part of their non-specific defence system. These peptides can offer protection against a wide variety of bacterial and fungal pathogens in plants. Due to the fact that phytoplasmas lack an outer membrane and cell wall, AMPs are considered to be perfect candidates to confer resistance to this phytopathogen. The current study intends to explore the in planta activity of AMPs against the grapevine pathogen aster yellows phytoplasma (AYp) through Agrobacterium-mediated transient expression. The AMPs, Vv-AMP1, D4E1 and Snakin1 (isolated from potato and grapevine) were selected to be tested for their in planta effect against AYp. Cauliflower mosaic virus 35S expression vectors containing four different AMP-encoding sequences were therefore constructed. As an alternative method to observe the effect Vv-AMP1 might have on AYp in planta, grafting of Vv-AMP1 transgenic Vitis vinifera cv "Sultana‟ plant material was used. To allow assumptions about AMP efficacy in this transient expression system, attempts were made to describe the spatial distribution and pathogen titre of AYp in V. vinifera cv "Chardonnay‟ material. Additionally, transmission experiments were carried out to infect Catharanthus roseus and Nicotiana benthamiana with AYp through the insect vector Mgenia fuscovaria. Material was screened for AYp infection by a nested-PCR procedure using universal primers described by Gundersen and Lee (1996). For quantification of AYp infection, a semi-quantitative real-time PCR (qPCR) protocol was optimized, using the SYBR Green-based system. In total, 86 V. vinifera cv "Chardonnay‟ plantlets were screened for AYp infection two-, three-, four-, seven- and eleven weeks after introduction into in vitro conditions. No AYp infection could however be detected and plantlets displayed a "recovery phenotype‟. To examine the distribution of AYp in canes of an infected V. vinifera cv "Chardonnay‟ plant, leaf and the corresponding node material from five canes were screened by a nested-PCR procedure. It can be concluded, that AYp was found predominantly in the nodes when compared to leaf material in the late season of the year. It is also highly unlikely for leaf material to show phytoplasma infection, if in the corresponding node no AYp could be detected. As AYp-infected grapevine material could not be maintained in vitro, the effect of VvAMP-1 transgenic grapevine against AYp could not be tested. Infection of C. roseus and N. benthamiana plants with AYp was successfully achieved by insect vector transmission experiments. Transient expression assays were conducted on AYp-infected N. benthamiana material. Quantification of phytoplasma in this material showed a decrease of AYp in both the AMP treatment groups and the control groups. This study optimized a qPCR procedure to detect and quantify AYp in infected plant material. The Agrobacterium-mediated transient expression system used during this study was not reliable, as no significant effect of the AMPs on AYp titre could be observed. This study showed, that AYp cannot be established and maintained in in vitro cultured V. vinifera cv "Chardonnay‟ material, and tissue culture itself might therefore be a way to eradicate AYp in this cultivar. To our knowledge, this study is the first to report on the spatial distribution of AYp in canes of an infected V. vinifera cv "Chardonnay‟ vine.
AFRIKAANSE OPSOMMING: Fitoplasma siektes veroorsaak ramspoedige gevolge in wingerde oor die hele wêreld. Dus kan die onlangse ontdekking van fitoplasma in Suid-Afrikaanse wingerde baie nadelige gevolge vir die plaaslike wynbedryf beteken. Antimikrobiese peptiede (AMPe) is klein molekules wat in amper al organismes as deel van hulle nie-spesifieke verdedegingsstelsel tot uitdruk kom. Hierdie peptiede kan beskerming aanbied teen ʼn wye verskeidenheid van bakteriële en swampatogene in plante. As gevolg van die feit dat fitoplasmas geen buitenste membraan en selwand het nie, word AMPe oorweeg as middle om weerstand te verleen teen hierdie fitopatogene. Die huidige studie beoog om die in planta aktiwiteit an AMPe teen die wingerdstok patogeen aster geel fitoplasma (AYp) deur middle van Agrobakteriumbemiddelde tydelike uitdrukkingssiteme, te ondersoek. Die AMPe, Vv-AMP1, D4E1 en Snakin1 (geïsoleer van aartappel en wingerd plante) is gekies om getoets te word vir hul in planta effek teen AYp. Blomkoolmosaïek-viruse 35S uitdrukkingsvektore met vier verskillende AMP-kodering rye, is dus ontwikkel. As ʼn aternatiewe method om die moontlike effek van Vv-AMP1 op AYp in planta in ag te neem, is oorplantings van die Vv-AMP1 transgeniese Vitis vinifera cv "Sultana‟ plantmateriaal gebruik. Om voorsiening te maak vir AMPe se doeltreffenheid in hierdie tydelike uitdrukkingsvektore, is pogings aangewend om die ruimlike verspreiding en patogeen konsentrasie van AYp in V. vinifera cv "Chardonnay‟ te beskryf. Addisioneel is transmissie eksperimente uitgevoer om Catharanthus roseus en Nicotania benthamiana te besmet met AYp deur die insekvektor, Mgenia fuscovaria. Plantmateriaal is getoets vir AYp deur van ʼn PCR protokol gebruik te maak met universele inleiers (grondlae) soos beskyf deur Grundersen en Lee (1996). Vir kwantifiseering van die AYp infeksie, is n semi-kwantitatiewe qPCR protokol geoptimaliseer, met hulp van die SYBR Groen-gebaseerde stelsel. In geheel is 86 V. vinifera cv "Chardonnay‟ planties getoets vir AYp infeksie – twee-, drie-, vier-, sewe- en elf weke na die bekendstelling aan die in vitro voorwaardes. Geen AYp infeksie kon egter opgespoor word en die plante het “herstel fenotipe‟ vertoon. Om die verspreiding van AYp in stingelknope van ʼn besemtte V. vinifera cv "Cardonnay‟ plant, blaar en ooreenstemmende stingelknope uit vyf stingels te ondersoek, is hulle getoets deur ʼn PCR protokol. Daar kon afgelei word dat AYp hoofsaaklik in die stingelknop in vergelyking met die blaarmaterial laat in die season, gevind word. Dit is hoogs oonwaarskynlik om fitoplasma infeksies in blaarmaterial te vind, as in die ooreenstemmende stingelknop daar geen AYp oopgespoor kon word nie. As gevolge daarvan dat die AYp-geinfekteerde wingerdmateriaal nie in vitro gegroei kon word nie, kon die effek van VvAMP-1 transgeniese wingerd teen AYp nie getoets word nie. Infeksies van C. roseus en N. benthamiana plante met AYp is suksesvol bereik deur transmissie eksperiemente. met ʼn insekvektor. Tydellike uitdrukkingvektore toetse is uitgevoer op die AYp besmette N. benthamiana material. Kwantifisering van fitoplasma in hierdie material het die afname van AYp in altwee, die AMP behandelings groepe en die kontrole groepe getoon. Hierdie studie het ʼn qPCR geoptimaliseer om besmette plantmaterial met AYp op te spoor en dit te kwantifiseer. Die Agrobacterium-bemiddelde tydelike uitdrukingsvektore wat in hierdie studie gebruik is, was nie vertroubaar genoeg, want geen beduidelike effek van die AMPe op AYp konsentrasie kon waargeneen word nie. Hierdie studie het bewys dat AYp nie vasgestel is en in stand gehou kan word deur in vitro aankweeking van V. vinifera cv "Chardonnay‟ material nie, en weefselkulture kan dus ʼn manier wees om AYp in hierdie kultivar uit te roei. Tot kennis, is hierdie studie die eerste studie om die ruimtelike verspreiding van AYp in stingelknope van ʼn besmette V. vinifera cv "Chardonnay‟ wingerstok te rapporteur.
Winetech and DAAD