Grapevines In South Africa Research Articles

Diversity of viroids infecting grapevines in the South African Vitis germplasm collection.

Seven viroid species and one putative viroid species have been reported to infect grapevine namely, hop stunt viroid (HSVd), grapevine yellow speckle viroid 1 (GYSVd-1), grapevine yellow speckle viroid 2 (GYSVd-2), Australian grapevine viroid (AGVd), Japanese grapevine viroid (JGVd), grapevine latent viroid (GLVd), and citrus exocortis viroid (CEVd), as well as a grapevine hammerhead viroid-like RNA (GHVd), so far. In this study, RNA sequence (RNA-Seq) data, from 229 Vitis accessions from the field-maintained vineyard of the South African Vitis germplasm collection, were analysed to determine the diversity of the viroids present. Five of the seven known grapevine-infecting viroids and one putative grapevine-infecting viroid species were very commonly found, with 214 of the 229 samples containing at least one viroid species. HSVd, GYSVd-1, GYSVd-2, AGVd, and JGVd, as well as GHVd, were identified in the RNA-Seq data of the samples and confirmed using RT-PCR and Sanger sequencing. The HSVd sequences indicated the presence of two variants, with one showing multiple nucleotide insertions. AGVd and GYSVd-2 did not display significant sequence diversity, confirming past international studies. GYSVd-1 occurs as four major variants worldwide and representatives of all four variants were identified in this vineyard. This is the first report on the diversity of viroids infecting grapevine in South Africa and the first report of JGVd outside of Japan and GHVd in South Africa. Further studies are needed to fully assess the population and to identify potentially new viroid species.

Predominant Clonal Reproduction with Infrequent Genetic Recombination of Phaeoacremonium minimum in Western Cape Vineyards.

Phaeoacremonium minimum is an important esca and Petri disease pathogen that causes dieback of grapevines in South Africa. Little is known regarding the reproductive strategy of the pathogen. Sexual reproduction could lead to a better adaptation of the pathogen to disease management strategies by combining alleles through recombination. The study aimed to investigate the genetic diversity and recombination potential of eight populations in the Western Cape, from six commercial vineyards and two nursery rootstock mother blocks. This was achieved by developing and applying nine polymorphic microsatellites and mating-type-specific markers. Thirty-seven genotypes were identified from 295 isolates. Populations were characterised by the same dominant genotype (MLG20 occurring 65.43%), low genotypic diversity (H) and high numbers of clones (81.36% of dataset). However, genotypes from the same sampling sites were not closely related based on a minimum spanning network and had high molecular variation within populations (94%), suggesting that multiple introductions of different genotypes occurred over time. Significant linkage disequilibrium among loci (r̅d) further indicated a dominant asexual cycle, even though perithecia have been observed in these four populations. The two rootstock mother blocks had unique genotypes and genotypes shared with the vineyard populations. Propagation material obtained from infected rootstock mother blocks could lead to the spread of more genotypes to newly established vineyards. Based on our results, it is important to determine the health status of rootstock mother blocks. Management strategies must focus on reducing aerial inoculum to prevent repeated infections and further spread of P. minimum genotypes.

Genome-Informed Design of a LAMP Assay for the Specific Detection of the Strain of 'Candidatus Phytoplasma asteris' Phytoplasma Occurring in Grapevines in South Africa.

Grapevine yellows is one of the most damaging phytoplasma-associated diseases worldwide. It is linked to several phytoplasma species, which can vary regionally due to phytoplasma and insect-vector diversity. Specific, rapid, and reliable detection of the grapevine yellows pathogen has an important role in phytoplasma control. The purpose of this study was to develop and validate a specific loop-mediated isothermal amplification (LAMP) assay for detection of a distinct strain of grapevine 'Candidatus Phytoplasma asteris' that is present in South Africa, through implementation of a genome-informed test design approach. Several freely available, user-friendly, web-based tools were coupled to design the specific LAMP assays. The criteria for selection of the assays were set for each step of the process, which resulted in four experimentally operative LAMP assays that targeted the ftsH/hflB gene region, specific to the aster yellows phytoplasma strain from South Africa. A real-time PCR was developed, targeting the same genetic region, to provide extensive validation of the LAMP assay. The validated molecular assays are highly specific to the targeted aster yellows phytoplasma strain from South Africa, with good sensitivity and reproducibility. We show a genome-informed molecular test design and an efficient validation approach for molecular tests if reference and sample materials are sparse and hard to obtain.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

First report of grapevine polerovirus 1 in South Africa

This is the first report of grapevine polerovirus 1 (GPoV-1) on grapevine in South Africa. It was detected in ‘Katta Khurgan’ and ‘Kandari’ cultivars, using an RNAtag-seq with Illumina HiSeq sequencing and RT-PCR. GPoV-1 was a component of mixed infections with other viruses, therefore further work will be required to establish associated symptomatology.

Genome-Informed Design of a LAMP Assay for the Specific Detection of the Strain of 'Candidatus Phytoplasma asteris' Phytoplasma Occurring in Grapevines in South Africa

Genome-Informed Design of a LAMP Assay for the Specific Detection of the Strain of 'Candidatus Phytoplasma asteris' Phytoplasma Occurring in Grapevines in South Africa

Aster yellows phytoplasma in grapevine in South Africa: insect vector management and alternative host plants

Aster yellows phytoplasma in grapevine in South Africa: insect vector management and alternative host plants

An Assessment of Treated Municipal Wastewater Used for Irrigation of Grapevines with Respect to Water Quality and Nutrient Load Assessment of TMW for vineyard irrigation

The impact of treated municipal wastewater (TMW) irrigation on soil and grapevines was assessed under field conditions in vineyards in the Coastal region of South Africa. Grapevines were irrigated using TMW from the City of Cape Town uninterruptedly over a period of 11 years. Grapevines were either rain fed, irrigated with TMW via a single dripper line, or received twice the volume via double dripper lines. The quality of the TMW used for vineyard irrigation was acceptable, and below the minimum criteria stipulated by the General Authorisations to irrigate up to 500 m3 per day in terms of pH, ECw and SAR. Mean Na+ concentration in the TMW exceeded the critical value of 100 mg/ℓ for irrigating grapevines in South Africa. The Cl- levels in the TMW were well below the threshold value of 700 mg/ℓ at which toxicity in grapevines might occur. Consistently high P concentrations measured in the TMW could lead to the formation of algal blooms in water storage facilities and bio-fouling of irrigation equipment. The low N content in the TMW could not supply the annual N requirement of grapevines. The annual amount of P applied via the single dripper lines was slightly below grapevine requirements, whereas double the TMW irrigation applied excessive amounts of P. Amounts of K+ applied via TMW irrigation was in excess of annual grapevine requirements, which could affect wine quality negatively. The amount of Ca2+ and Mg2+ applied via the TMW also exceeded annual grapevine requirements.

Genome-informed design of a LAMP assay for specific detection of aster yellows phytoplasmas occurring in grapevines in South Africa

Genome-informed design of a LAMP assay for specific detection of aster yellows phytoplasmas occurring in grapevines in South Africa

Diaporthe nebulae sp. nov. and First Report of D. cynaroidis, D. novem, and D. serafiniae on Grapevines in South Africa.

Diaporthe species cause Phomopsis cane and leaf spot as well as Phomopsis dieback on grapevines. Symptoms of Phomopsis dieback have increasingly been observed over the past few years. In order to assess the current status of Diaporthe on grapevines in the Western Cape Province of South Africa, isolations were made from dormant grafted nursery vines, dormant rootstock canes, and dying or dead spurs of field vines. Cultures identified as Diaporthe based on morphological features were further identified to species level by sequencing the internal transcribed spacers (ITS) 1 and 2 and 5.8S rRNA and, for a representative subsample of isolates, the partial beta-tubulin (tub2) and translation elongation factor 1-alpha (EF1-α) genes. Phylogenetic analysis of the combined ITS, tub2, and EF1-α data revealed nine Diaporthe species associated with grapevines during this survey. One of these represents a new species, D. nebulae sp. nov., and three other species, namely D. novem, D. cynaroidis, and D. serafiniae, are reported on grapevines in South Africa for the first time. Species-specific primers were designed for PCR identification of D. ampelina, D. ambigua, and D. foeniculina. Pathogenicity studies conducted on detached grapevine shoots indicated D. ampelina, D. novem, and D. nebulae sp. nov. as the most virulent species.

Foliar Application of Steinernema yirgalemense to Control Planococcus ficus: Assessing Adjuvants to Improve Efficacy

The vine mealybug (Planococcus ficus) is regarded as a key mealybug pest of grapevines in South Africa, with entomopathogenic nematodes (EPNs) being touted as a potential alternative to chemical control, although their vulnerability to above-ground environmental conditions has limited their use. In this study, tests were conducted to assess the ability of adjuvants to increase the deposition of S. yirgalemense on grapevine leaves. The combination of Nu-Film-P® and Zeba® resulted in significantly more infective juveniles (30) being deposited per 4 cm2 leaf disc than with either the control (14.8), or with Nu-Film-P® (23.3), although not significantly more than with Zeba® alone (29.2). The ability of S. yirgalemense, in conjunction with the two adjuvants, to control P. ficus on grapevine foliage was then assessed under controlled conditions. The application of S. yirgalemense with both Zeba® and Nu-Film-P® to P. ficus on leaf discs in a growth chamber resulted in 84% mortality, significantly greater than that attained by the application of S. yirgalemense with either Zeba® (47%), or water alone (26%). Similar results were observed in a glasshouse trial, in which the combination of S. yirgalemense, Zeba® and Nu-Film-P® offered 88% control of P. ficus on leaf discs hung on potted vines, compared with the control that was achieved with S. yirgalemense with either Zeba® (56%) or water alone (30%). This study demonstrates the potential of a combination of S. yirgalemense with adjuvants to give significant control of P. ficus on grapevine foliage, compared with using EPNs alone.

Identification of Mgenia fuscovaria (Stål)(Hemiptera: Cicadellidae), a vector of aster yellows disease on grapevines in South Africa, and differentiation from Mgenia angusta (Theron) by nucleotide sequences of the mitochondrial cytochrome oxidase I (cox1) gene

Aster yellows phytoplasma (AY), only recently reported in South Africa and still limited in its distribution in the country, causes a serious disease of grapevine. A leafhopper, Mgenia fuscovaria (Stal)(Hemiptera: Cicadellidae), was shown to transmit AY to grapevine (Vitis vinifera L.) locally. A second Mgenia species, identified as Mgenia angusta (Theron), has also been found in vineyards in South Africa but has not been shown to transmit AY. M. angusta is morphologically similar to M. fuscovaria, but does differ regarding the size of the male sex organ and in the number of teeth of the blades making up the ovipositor. In this study, we determined the nucleotide sequence of the mitochondrial cytochrome oxidase I gene (cox1), commonly used in insect bar-coding, of a number of specimens of males, females and nymphs of both M. fuscovaria and M. angusta. No differences were observed between the cox1 sequences of the male, female and nymph specimens putatively assigned to any specific species, but some nucleotide sequence differences were observed between specimens of M. fuscovaria and M. angusta. These differences, however, were insufficient to allow the development of PCR systems specific to each species.

Pathogenicity of ten Phaeoacremonium species associated with esca and Petri disease of grapevine

CITATION: Baloyi, M., Mostert, L. & Halleen, F. 2018. Pathogenicity of ten Phaeoacremonium species associated with esca and Petri disease of grapevine. Phytopathologia Mediterranea, 57(3):538-546, doi:10.14601/Phytopathol_Mediterr-23940.

Diversity of Diatrypaceae Species Associated with Dieback of Grapevines in South Africa, with the Description of Eutypa cremea sp. nov.

Recent studies in grape-growing areas including Australia, California, and Spain have revealed an extensive diversity of Diatrypaceae species on grapevines showing dieback symptoms and cankers. However, in South Africa, little is known regarding the diversity of these species in vineyards. The aim of this study was, therefore, to identify and characterize Diatrypaceae species associated with dieback symptoms of grapevine in South Africa. Isolates were collected from dying spurs of grapevines aged 4 to 8 years old, grapevine wood showing wedge-shaped necrosis when cut in cross section as well as from perithecia on dead grapevine wood. The collected isolates were identified based on morphological characters and phylogenetic analyses of the internal transcribed spacer region (ITS) and β-tubulin gene. Seven Diatrypaceae species were identified on grapevine, namely Cryptovalsa ampelina, C. rabenhorstii, Eutypa consobrina, E. lata, E. cremea sp. nov., Eutypella citricola, and E. microtheca. The dying spurs yielded the highest diversity of species when compared with the wedge-shaped necrosis and/or perithecia. C. ampelina was the dominant species in the dying spurs, followed by E. citricola, whereas E. lata was the dominant species isolated from the wedge-shaped necroses and perithecia. These results confirm E. lata as an important grapevine canker pathogen in South Africa, but the frequent association of C. ampelina with spur dieback suggests that this pathogen plays a more prominent role in dieback than previously assumed. In some cases, more than one species were isolated from a single symptom, which suggests that interactions may be occurring leading to decline of grapevines. C. rabenhorstii, E. consobrina, E. citricola, E. microtheca, and E. cremea are reported for the first time on grapevine in South Africa.

Slow Dieback of Grapevine in South Africa: Stress-Related Predisposition of Young Vines for Infection by Phaeoacremonium chlamydosporum

Phaeoacremonium chlamydosporum causes slow dieback of nursery vines and young vines in vineyards. In a greenhouse trial it was observed that significantly more inoculated Chenin blanc vines grafted onto rootstock 101-14 Mgt, and subjected to water stress, exhibited dieback symptoms. More plants eventually died compared to inoculated vines not subjected to stress. Inoculation technique (stem inoculation vs soil inoculation) did not significantly affect disease incidence. Extensive plugging of the xylem tissue in inoculated plants was observed, eventually leading to slow dieback of these vines.

Fungi Associated with Dieback and Pruning Wounds of Grapevines in South Africa

Isolations were made from discoloured tissue of grapevines showing dieback symptoms in the winter rainfall region. Fifteen fungal species were isolated, of which Sphaeropsis sp. Fusarium oxysporum, Eutypa lata (anamorph: Libertella blepharis A.L. Smith), Pestalotia quepini and Botrytis cinerea could be designated as parasites. E. lata was the most probable cause of the dieback phenomenon. Additional isolates representing ten fungal genera were isolated from discoloured wood in spurs from visually healthy grapevines while organisms representing 14 genera were isolated from lesions in grapevines exhibiting dieback symptoms. Aspergillus sp. was more common in the healthy and marginal zones while Sphaeropsis sp. occurred more often in the healthy zone and Phylosticta sp. in the discoloured zone of pruning stubs. In lesions from vines with dieback symptoms, Altemaria alternata was isolated more regularly from the marginal zone between healthy and discoloured wood, while E. lata and Trichoderma harzianum were isolated more often from the older part of the lesion. A succession of fungi in the colonisation of pruning wounds and in dieback lesions is suggested.

Metalaxyl Sensitivity Status of Downy Mildew Populations in Western Cape Vineyards

Grapevine downy mildew, caused by Plasmopara viticola, is a sporadic, but destructive disease of grapevines in South Africa. Despite extensive fungicide spray programmes, disease control during disease-conducive weather periods is often inadequate, and severe losses were experienced during recent epidemics. Poor disease control can be attributed to several factors, one of which may be reduced efficacy of fungicides due to resistance build-up in the pathogen populations. P. viticola isolates were sampled during the 1999/2000, 2000/2001 and 2001/2002 seasons from various vineyards in the Western Cape province of South Africa and screened for sensitivity to metalaxyl using the floating leaf-disc method recommended by the Fungicide Resistance Action Committee. Minimum inhibitory concentration (MIC) values for 813 isolates were determined. Only 5.8% of the isolates tested had MIC values of 10 μg/mL and lower. The majority of the isolates (94.2 % ) showed MIC values of 100 μg/mL or more. These isolates were designated resistant to highly resistant. With the exception of one vineyard in a remote area where phenylamides had not previously been used, very high resistance frequencies were observed, irrespective of whether the samples were taken early or late in the season. This observation, supported by the consistent high resistance frequencies recorded over time in individual vineyards, is indicative of the stability of metalaxyl resistance in grapevine downy mildew populations. In view of the widespread occurrence and stability of resistance against metalaxyl, the use of phenylamide formulations for the control of downy mildew in Western Cape vineyards should be reconsidered.

A new species of Phellinus sensu stricto associated with esca on grapevine in South Africa

A new species of Phellinus sensu stricto was isolated from diseased Vitis vinifera in the Northern Cape and Limpopo provinces of South Africa. Phellinus resupinatus is described here based on fruit body morphology, internal transcribed spacer (ITS) and large subunit (LSU) phylogenies. Phellinus resupinatus forms a well-supported clade closely related to Phellinus bicuspidatus, a species associated with white rot in oak trees in the United States. Morphologically, P. resupinatus is characterised by its resupinate fruit body shape, straight, ventricose hymenial setae and broadly ellipsoid hyaline basidiospores. It has been isolated from esca-diseased grapevines in the summer rainfall regions of South Africa and is found on the uppermost trunks of declining vines showing symptoms of white rot.

Brief report of the construction of infectious DNA clones of South African genetic variants of grapevine virus A and grapevine virus B.

BackgroundRecent research results strongly suggest that certain genetic variants of grapevine virus A (GVA) and grapevine virus B (GVB), two members of the Vitivirus genus of the family Betaflexiviridae, are the cause of Shiraz disease and corky bark disease of grapevines in South Africa, respectively. To investigate this hypothesis, work was undertaken to construct DNA clones of these viruses.Findings and conclusionsBiologically viable and stable DNA clones of genetic variants of GVA and GVB B from South Africa were constructed. The clones share 76.3, 73.2 and 85.2, 77.6 % nt sequence similarity with corresponding clones constructed in Italy and Israel. The results suggest that a derivative of a mini binary vector pCB302 is superior to pCAMBIA1305.1 for the construction of infectious and stable DNA clones of vitiviruses. Successful construction of such DNA clones of GVA and GVB reported in this study is a clear step towards fulfilling Koch’s 3rd postulate in investigating the aetiology of Shiraz disease and corky bark disease.

Identification of the Female-Produced Sex Pheromone of the Leafminer Holocacista capensis Infesting Grapevine in South Africa.

We report the first identification of a sex pheromone in a heliozelid moth, Holocacista capensis van Nieukerken & Geertsema. This leafminer recently infested grapevine in South Africa. Compared to solvent extraction of pheromone glands, solid phase microextraction (SPME) proved to be highly effective for collection of the pheromone from calling females. The volatiles collected by SPME were analyzed by gas chromatography with electroantennographic detection (GC/EAD). Three compounds eliciting electrophysiological activity from the male antenna were identified as (Z)-5-tetradecenal, (Z)-7-tetradecenal, and (Z)-9-hexadecenal by coupled gas chromatography–mass spectrometry (GC/MS). GC/MS analysis of dimethyldisulphide (DMDS) derivatives of fatty acyl moieties in pheromone gland extracts confirmed the presence of the corresponding putative pheromone precursors with double bonds in the same position and with Z geometry. Field trapping experiments in a South African vineyard confirmed that both (Z)-5-tetradecenal and (Z)-7-tetradecenal are essential for the attraction of male H. capensis, whereas addition of (Z)-9-hexadecenal to the blend did not affect the attractiveness. The composition of the pheromone is discussed in relation to the phylogeny of this family of moths.

Multigene characterization of aster yellows phytoplasmas infecting grapevine in South Africa

The genetic diversity of aster yellows phytoplasmas in grapevine collected in two locations in South Africa (Vredendal and Robertson) was investigated by the use of multilocus analysis of gene sequences amplified by polymerase chain reaction. Based on results from restriction fragment length polymorphism profiling and nucleotide sequence alignments of 16S rRNA, rp, amp, groEL and secY genes in comparison with aster yellows strains from Italy and reference aster yellows strains, four lineages have been detected in samples from South Africa.