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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. [ABSTRACT FROM AUTHOR]

Colomerus vitis is a pest of grapevine worldwide that includes three strains recognised by plant symptoms (bud, erineum, and leaf curl), which could represent cryptic species. We approached this long-standing question by integrating genetic and morphological methods. COI sequences of mites from South Africa and other countries showed five phylogenetic groups (G1 to G5) with intergroup p-distances up to 23% and intragroup divergence lower than 2%. The three groups found in South Africa (G1, G2, and G3) were screened from a variety of grapevine samples using a novel multiplex PCR method. Only G1 and G3 were significantly associated with erinea and buds, respectively, and the three groups were frequently co-present in the same plant sample. Cryo-SEM showed adults with five- and six-rayed empodia, variable microtubercle shape, and prodorsal shield patterns. Specimens with six-rayed empodia and a smooth prodorsal shield were more often associated with buds, while specimens from erinea were variable. These results support the genetic evidence in that particular groups or morphotypes are not associated exclusively with specific plant niches. We propose that C. vitis is a complex of at least five genetically distinct but morphologically similar species, and that no one species can be assigned to a particular grapevine symptom. [ABSTRACT FROM AUTHOR]

Pathogenicity of Fusarium euwallaceae, a mutualist of the Euwallacea fornicatus beetle, was assessed on apple and grapevine following its first detection on these hosts in South Africa. Fusarium euwallaceae caused lesions in xylem tissues of apple (Pink Lady), but not grapevine (Merlot and Cabernet Sauvignon). Koch's postulates were satisfied through re-isolation from artificially inoculated tissues. [ABSTRACT FROM AUTHOR]

Entomopathogenic nematodes (EPNs) are insect parasites that are used successfully as biological control agents against key pest insects of grapevine. To achieve low chemical residues and the sustainable production of grapes, it is important that biological control agents such as entomopathogenic nematodes for the control of grapevine insect pests be incorporated in an integrated pest management system for grape production. However, the commercialisation and large-scale use of EPNs is limited by their short shelf life in formulations and in storage, thus leading to poor quality and reduced efficacy against insects in the field. In South Africa, interest in the use of EPNs within an integrated pest management system has grown over the past two decades, therefore developing a formulation technique with an acceptable storage survival period, while maintaining infectivity, is essential. Moreover, the successful control of insects using EPNs is only achievable when the formulated product reaches the end user in good condition. This review is focused on the different types of formulations required for storage and ease of transport, together with the application formulation for above-ground pests and the factors affecting them. The quality assessment, storage and handling of formulated EPNs are also discussed. [ABSTRACT FROM AUTHOR]

High-throughput sequencing (HTS) was used to construct the virome profile of an old grapevine-leafroll-diseased grapevine (Vitis vinifera). De novo assembly of HTS data showed a complex infection, including a virus sequence with similarity to viruses of the genus Badnavirus, family Caulimoviridae. The complete genome sequence of this virus consists of 7090 nucleotides and has four open reading frames (ORFs). Genome organisation and phylogenetic analysis identify this virus as a divergent variant of grapevine Roditis leaf discoloration-associated virus (GRLDaV) with 90% nucleotide sequence identity to isolate w4 (NC_027131). This is the first genome sequence of a South African variant of GRLDaV. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (Stål)(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. [ABSTRACT FROM AUTHOR]

Grapevine is host to twoColomerusspecies:Colomerus vitis(Co. vitis), distributed worldwide; andColomerus oculivitis(Co. oculivitis), restricted to Egypt and Saudi Arabia. Both these eriophyid species, as well asColomerusspecimens morphologically near them, were intercepted by South African officials on table grapes and grapevine budwood imported from a number of different countries.Colomerus oculivitismay have a wider distribution than reported and/or its taxonomy may be erroneous. In addition, breeding colonies ofColomerusmites were found on imported fresh table grapes. This represents an unconsidered introduction pathway for eriophyoids on grapevine. A survey and taxonomic study on grapevine eriophyoid mites are presently underway in South Africa. Due to taxonomic uncertainties, it is our opinion thatColomerusmites from grapevine worldwide cannot be identified accurately to species. [ABSTRACT FROM AUTHOR]

Grapevine virus A ( GVA), a member of the genus Vitivirus which belongs to the family Flexiviridae, has a single-stranded RNA genome of about 7.4 kb that comprises five open reading frames ( ORFs). ORF5 encodes a small 10-kDa protein (p10), which is believed to interact with nucleic acids and to suppress the plant's RNA -silencing response. We obtained molecular and biological data indicating that ORF5-encoded product, specifically its N-terminus, affects the appearance of symptoms in Nicotiana benthamiana plants. The ORF5-encoded products of the severe GR5 and the mild GTR1-1 isolates were found to affect RNA silencing similarly in mesophyll cells of N. benthamiana, despite being involved in different expressions of symptoms on this host. [ABSTRACT FROM AUTHOR]

In the past, only a few incidences of esca diseased grapevines were reported from the Slanghoek and Rawsonville areas of South Africa. The damage was believed to be of little importance and therefore the disease has not been studied in South Africa. In the present study, vines with internal or external symptoms of the esca disease complex were sampled from table, raisin and wine grape cultivars from 37 production areas in the Western Cape, Northern Cape and Limpopo provinces of that country. Most vines were greater than 10 years old, but younger vines (3 and 5 years old) were also found to be infected. External symptoms, including dieback, tiger striped leaves, berry symptoms (shrivelling, insufficient colouring) and apoplexy, resembled those found on grapevines in Europe and the USA, although the typical tiger stripe symptom was observed less frequently. The internal stem and trunk symptoms were similar to European symptoms, and included white rot, black and brown wood streaking, brown necrosis within white rot, sectorial brown necrosis and brown/red/margins next to decay, which often included black lines delimiting white decay. The fungi isolated mostly from the white rot were basidiomycetes species (30.4 %). Black and brown wood streaking was primarily caused by Phaeomoniella chlamydospora (45.4%). Brown necrosis within the white rot was linked to colonization by basidiomycetes (20.4%), Phaeoacremonium aleophilum (15.9%) and Pa. chlamydospora (13.6%). Phaeomoniella chlamydospora (20.8%) and Botryosphaeriaceae species (10.7%) were isolated the most from the sectorial brown necrosis and Pa. chlamydospora (29.1%) from the brown/red margins and black lines next to decay. Given the wide distribution of esca complex wood and foliar symptoms in the grape growing regions investigated, this disease should be considered as an important limiting factor in the productive lifespan of vineyards and the quality of produce from grapevine in South Africa. [ABSTRACT FROM AUTHOR]

Grapevine trunk diseases, caused by a range of phytopathogenic fungi, represent a serious impediment to wine and table grape production wherever these crops are cultivated. Previous studies have shown that the distribution of these pathogens is influenced by climate and that they are associated with a variety of internal wood decay symptoms. Little was known, however, about the influence of climate on the disease symptomatology of the different pathogens in a specific area. To address this, a survey was conducted in 30 wine and table grape vineyards in summer, marginal and winter rainfall regions of South Africa. Apart from Eutypa lata, which occurred only in the winter rainfall region, Phaeomoniella chlamydospora, species of Phaeoacremonium, Botryosphaeriaceae and Phomopsis occurred in all regions surveyed. The incidence of the fungal genera and species associated with trunk disease varied between regions, with overlapping symptom profiles that differed based on the climatic region. These findings suggest that symptom-based disease diagnosis alone is unreliable and that distribution and symptomatology of grapevine trunk pathogens are strongly influenced by climatic conditions in a specific production region. [ABSTRACT FROM AUTHOR]

Eutypa lata and Phaeomoniella chlamydospora, as well as several species in Botryosphaeriaceae, Phomopsis and Phaeoacremonium are known trunk pathogens of grapevines, which use pruning wounds as infection portals. Duration of pruning wound susceptibility to some of these pathogens was largely unknown. To address this question, plants of the cv. Chenin Blanc in a vineyard in the Stellenbosch area of South Africa were pruned at two stages, and then spray-inoculated with spore suspensions of E. lata, Pa. chlamydospora, Neofusicoccum australe and Phomopsis viticola directly after pruning, and 1, 2, 3, 7, 10, 14, 17 and 21 days after pruning. Eight months after inoculation, pathogen incidence in the treated wounds was determined by means of isolation from the pith and xylem tissue of treated plants. Lesions observed in these tissues were also measured and recorded. Results indicated that, irrespective of pathogen inoculated, pathogen incidence in the inoculated pruning wounds of both mid- and late winter declined with increasing wound age. The rate of decline was much slower in 2004 compared to 2005; however, wounds remained susceptible for 3 or more weeks after pruning in both years. Late winter wounds were more susceptible to infection than wounds made earlier in the season, while xylem tissue of pruning wounds generally proved more susceptible to all pathogens compared to exposed pith tissue. [ABSTRACT FROM AUTHOR]

When a recently discovered 234-nt fragment of the Grapevine virus A (GVA) genome, located in ORF3, was used in single-strand conformation polymorphism (SSCP), it produced patterns of DNA bands which were indicative of GVA variants of molecular group II. This technique of rapid identification of variants of group II was applied to the study of GVA variants in various grapevines with different Shiraz disease (SD) status. The results, supported by nucleotide sequence data, revealed that GVA variants of molecular group II are closely associated with SD in South Africa, and showed that variants of group III are commonly present in SD-susceptible grapevines that consistently do not exhibit symptoms of this disease. [ABSTRACT FROM AUTHOR]

Petri disease is a vascular disease associated with decline and dieback of young grapevines. A major means of spread of the causal organisms, Phaeomoniella chlamydospora and Phaeoacremonium spp., is via infected propagation material. Since no curative control measures are known, proactive measures must be taken in grapevine nurseries to manage this disease. To study this aspect, semicommercial trials with naturally infected rootstock material were performed in grapevine nurseries in South Africa. Prior to grafting, rootstocks were treated as follows: l-h drench in suspensions of benomyl, phosphoric acid, different bacterial and Trichoderma formulations, water, or hot water treated (HWT; 30 min at 50°C). Grafted cuttings were planted and grown in a greenhouse and two commercial field nurseries and uprooted 8 months later. In instances where rootstocks were treated with benomyl or Trichoderma formulations, the incidences of Phaeomoniella and Phaeoacremonium in grafted cuttings and uprooted nursery vines were significantly lower than that of the water treatment. However, the reduction was most consistent and noteworthy in vines on rootstocks that received HWT prior to grafting. HWT of dormant nursery vines effected a similar reduction in Phaeomoniella and Phaeoacremonium incidence. Root-stock drenches in benomyl and/or Trichoderma formulations could thus be integrated with HWT for the proactive management of Petri disease in grapevine nurseries. [ABSTRACT FROM AUTHOR]

Presents an abstract of research entitled `Frequency of Dicarboximide and Benzimidazole Resistant Strains of Botrytis Cineria in Western Cape Table Grape Vineyards and Influence of Spray Schedules on Dicarboximide-Resistant Populations,' by P.H. Fourie and G. Holz.

Presents an abstract of the study `Monitoring resistance of Botrytis cinerea to dicarboximide fungicides on table grapes in the Western Cape,' by P.H. Fourie and G. Holz which was presented at the 33rd annual congress of the South African Society for Plant Pathology held from January 15-18, 1995 in South Africa.

Presents an abstract of the study `Resistance in Botrytis cinerea to dicarboximide fungicides on table grapes,' by P.H. Fourie and G. Holz presented at the 32nd annual congress of the South African Society for Plant Pathology held at the Aventura Vaal Spa, Christiana, South Africa from January 23-26, 1994.