Doctoral Degrees (Plant Pathology)
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Browsing Doctoral Degrees (Plant Pathology) by browse.metadata.advisor "Halleen, Francois"
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- ItemThe characterisation of basidiomycetes associated with esca disease in South African grapevines(Stellenbosch : Stellenbosch University, 2015-03) Cloete, Mia; Mostert, Lizel; Halleen, Francois; Stellenbosch University. Faculty of Agrisciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Esca is a disease complex of grapevine that includes different foliar and vascular symptoms caused by various fungal pathogens. One of the distinguishing characteristics of the disease on mature vines is the white rot of the wood. Esca-related wood rot is caused by several lignicolous basidiomycetes from the order Hymenochaetales. The Hymenochaetales fungi associated with esca vary depending on geographic location. For example, in Europe and the Mediterranean grape-growing regions, Fomitiporia mediterranea is the prevalent species; in Argentina, Inocutis jamaicensis; in Chile “Fomitiporella vitis”, and in Australia Fomitiporia australiensis. In the United States, Fomitiporia polymorpha has been associated with esca, though not consistently. A previous study identified ten different taxa belonging to the genera Fomitiporella, Fomitiporia, Inocutis, Inonotus, and Phellinus associated with esca in South Africa. The current study was tasked with characterising these taxa and assessing their epidemiology and pathogenicity. The study has characterised three novel species, Fomitiporella viticola, Fomitiporia capensis and Phellinus resupinatus from Vitis vinifera and a first report of Inonotus setuloso-croceus occurring on Vitis vinifera and Salix spp. worldwide and in South Africa. The sporulation of F. viticola was surveyed over two seasons. The pathogenicity of all ten taxa was tested on mature field grown vines and enzymes secreted by all ten taxa were assayed. This study aimed to add in the understanding of the esca complex disease in South Africa and contributed towards the wider knowledge regarding the ecology of the Hymenochaetales. A novel Fomitiporia species, F. capensis, was described based on fruit body morphology and combined internal transcribed spacer rRNA ITS1-5.8S-ITS-2 (ITS) and large sub-unit (LSU) phylogeny, where it formed a clearly delineated and well-supported clade. Morphologically, F. capensis was similar to F. punctata in that both species essentially lack setae. Fomitiporia capensis, F. punctata and F. aethiopica produced similarly sized basidiospores, but differed in terms of host range, pore size and, possibly, fruiting body shape. Phylogenetically, F. capensis appeared to be related to F. tenuis, though morphologically the species differed significantly in that F. tenuis had smaller pores and smaller basidiospores. During all surveys conducted, Fomitiporia capensis was found to occur widely as throughout the Western Cape Province, though fruit bodies were scarce in comparison to mycelium isolated from symptomatic vines. Fruit bodies were also found in a vineyard in the Limpopo region in the north east part of the country. Phellinus resupinatus was described based on fruit body morphology, ITS and LSU phylogenies. It formed 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 was characterised by its resupinate fruit body shape, straight, ventricose hymenial setae, and broadly ellipsoid hyaline basidiospores. It was only found on diseased grapevines in the summer rainfall regions of South Africa, mainly in the Northern Cape and Limpopo provinces. Fomitiporella viticola was described from Vitis vinifera based on fruit body morphology and ITS phylogeny. It is characterised by a resupinate to effuse-reflexed fruit body with large, loosely spaced pores and fairly small yellowish-brown basidiospores. Inonotus setuloso–croceus was found occurring on Salix and Vitis vinifera and was identified based on fruit body morphology. The ITS region was sequenced from DNA isolated from cultures obtained from rotten wood or fruit bodies, and was matched to the Hymenochaetales species from Vitis previously classified as Taxon 7. The discovery of Inonotus setuloso-croceus on Salix validated the hypothesis that fruit bodies may occur on alternative hosts. Fomitiporella viticola was often isolated from white rot on vines affected by esca and fruit bodies were often found on vines in the Western Cape Province. Twelve fruit bodies of F. viticola were monitored for sporulation weekly over two seasons lasting between winter and early summer. Levels of sporulation had a weak positive correlation with rainfall and a weak negative correlation with average temperature. Sporulation was found to occur throughout the entire monitoring period. Little is known about the pathogenicity and aetiology of the Hymenochaetales taxa associated with esca in South Africa. All ten taxa were subjected to enzyme assays to determine which ligninolytic enzymes were secreted by each taxon. In addition, a field trial was undertaken to determine the pathogenicity of ten South African Hymenochaetales taxa associated with esca in grapevine. Twenty-seven fungal isolates and two negative controls were inoculated into mature grapevines and incubated for 24 months. The results of the enzyme assays indicated a difference in enzyme secretion between taxa and also among isolates of the same taxa. All isolates secreted cellulase and laccase, but there was a difference between isolates‟ ability to secrete manganese peroxidase and lignin peroxidase. The results of the pathogenicity trial showed that all of the isolates used were capable of causing the characteristic white rot symptom in the wood. There were also clear differences in susceptibility to white rot between the two cultivars tested. Cultivars also differed in which taxa proved pathogenic. On Shiraz, Taxon 6 (an Inonotus sp.), Phellinus resupinatus and Inonotus setuloso-croceus were significantly virulent. On Mourvédre, however, Taxon 3, an Inocutis sp. and Taxon 2, a Fomitiporella sp. were significantly virulent. Cultivar differences could be due to various factors, including differences in host response to colonisation and physical differences in wood structure, as well as the differences in enzyme secretion between taxa.
- ItemCharacterisation, epidemiology and management of olive trunk disease pathogens in South Africa(Stellenbosch : Stellenbosch University, 2020-04) Van Dyk, Meagan; Halleen, Francois; Mostert, Lizel; Spies, Chris, F. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: The Olive Sector Development Plan of the Department of Trade and Industry identified low production and the lack of local research as weaknesses of the olive industry in South Africa. The management of trunk diseases forms an integral part of practices aimed at increasing olive production. A recent olive trunk disease survey performed in the Western Cape Province, South Africa, identified an undescribed Pseudophaeomoniella sp. as the most prevalent fungus associated with the trunk disease symptoms, with other fungal species occurring at much lower frequencies. In the current study, 40 of these isolates were selected for a pathogenicity study. The species forming lesions included several Botryosphaeriaceae, Phaeoacremonium and Phaeomoniellaceae species, as well as Biscogniauxia mediterranea, Coniochaeta velutina, Diaporthe foeniculina, Didymocyrtis banksiae, Eutypa lata, Pleurostoma richardsiae, Symbiotaphrina buchneri, isolates of the Cytospora pruinosa complex, and a Cytospora sp., Fomitiporella sp., Geosmithia sp. and Punctularia sp. The Pseudophaeomoniella sp. formed among the longest lesions, affirming its status as a potentially important trunk pathogen. Long distance dispersal of olive trunk pathogens is expected to occur via infected nursery material, similar to that found in other systems such as in grape and fruit trees. Nurseries as an inoculum source was investigated by making isolations from asymptomatic cuttings from mother blocks (Stage 1), rooted cuttings (Stage 2) and 1–2-year-old trees (Stage 3) of eight cultivars in two nurseries. Known olive trunk pathogens of the Botryosphaeriaceae, Diaporthaceae, Nectriaceae, Phaeomoniellaceae, Pleurostomataceae and Togniniaceae were recovered. Neofusicoccum australe was detected in a single Stage 1 cutting. Stage 3 material showed the highest incidence of fungi from these families, with P. richardsiae having the highest incidence in both nurseries (82.2% and 36.7% of the 1–2-year-old trees). Phaeoacremonium parasiticum was present in 28.9% of the trees from one nursery (Stage 3). The remaining pathogens occurred in 13.3% or less of the material. Pseudophaeomoniella sp. was present in the nurseries but at low frequencies. This suggests that alternative inoculum sources of this pathogen exists. A nested species-specific PCR was developed for the detection of Pseudophaeomoniella sp. from spore washes of pruning debris collected from established olive orchards. Pruning debris identified with a positive PCR was evaluated microscopically. Pycnidia of Pseudophaeomoniella sp. were observed on the pruning debris. Based on previous research, it is expected that the spore release coincides with rainfall and that the spores can be dispersed onto pruning wounds. The susceptibility of wounds from winter and spring pruning to Pseudophaeomoniella sp. was compared. Two-year-old olive branches of 16-year-old olive trees were pruned and inoculated with spore suspensions of Pseudophaeomoniella sp. at different time-points after pruning. The pruning wounds were susceptible for up to 42 days, with no difference between seasons (winter vs. spring). The wounds were the most susceptible within the first week after pruning. Eleven pruning wound protectants were evaluated and applied on pruning wounds made on 16–17-year-old trees directly after pruning. The treated wounds and positive (non-treated) controls were challenged with spore suspensions of Pseudophaeomoniella sp. at 1 or 7 days after pruning. Under low inoculum pressure (first season), Garrison, MT1, Neocil Plus and Tree Seal, reduced Pseudophaeomoniella sp. infections, while the Trichoderma-based protectant, MT1, was considered the most effective water-based protectant. Under higher inoculum pressure (during the second season), Tree Seal and Coprox Super/Bendazid consistently performed the best. In conclusion, several fungal species were identified as olive trunk pathogens, with Pseudophaeomoniella sp. being identified as one of the most important olive trunk pathogens. The propagation process was identified as a source of inoculum for some pathogens, including Pseudophaeomoniella sp. Inoculum sources of Pseudophaeomoniella sp. were also identified in established orchards. Olive pruning wounds are susceptible to Pseudophaeomoniella sp. for prolonged periods. MT1 was highly effective under lower inoculum pressure, while Tree Seal and Coprox/Bendazid were highly effective under high inoculum pressure. This study led to new knowledge with regards to olive trunk diseases, their pathogenicity, detection, epidemiology and control which can be used for the development of improved management strategies of olive trunk diseases in South Africa.
- ItemThe diversity and epidemiology of Botryosphaeriaceae species associated with grapevines and woody hosts surrounding vineyards in South Africa(Stellenbosch : Stellenbosch University, 2020-12) Du Plessis, Ihan Lambert; Halleen, Francois; Mostert, Lizel; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Botryosphaeriaceae species are reported globally as causal agents of grapevine trunk diseases which translate to yield losses as well as a reduction in the productive lifespan of affected vines. Growers rely on management practises to try and prevent vines from becoming infected. However, despite decades of implementation, current disease management strategies do not fully protect grapevines from becoming infected. This highlights a need for an improved understanding of the epidemiology of these pathogens as well as the development of improved disease management strategies. The aim of this study was to investigate the diversity of Botryosphaeriaceae species occurring on both grapevines as well as other woody hosts within the wine growing regions of the Western Cape Province. In addition, the potential threat that these other hosts pose to the grapevine industry by acting as sources of pathogen inoculum was investigated by characterizing and comparing different populations of the pathogen N. stellenboschiana isolated from both grapevines as well as non-grapevine hosts. The species diversity survey reported 20 different Botryosphaeriaceae species from 38 different host species which were located within 50 m of vineyards. These represented 114 different host/ fungi combinations which were not previously known in South Africa. This survey was dominated by three Botryosphaeriaceae species, Diplodia seriata, Neofusicoccum australe and N. stellenboschiana which constituted 85.1% of all the isolates obtained during this survey. These species are also known grapevine pathogens and were reported from 19, 11 and 24 different host species respectively which highlights the broad host range of these economically important pathogens. The species diversity survey also yielded six new Botryosphaeriaceae species which were formally described and their pathogenicity towards grapevines and olive trees, where relevant, were assessed through field pathogenicity trials. All of the new species were shown to form lesions on grapevine or olive shoots which were comparable to those caused by known Botryosphaeriaceae pathogens, demonstrating the capacity of these species to act as pathogens of these economically important hosts. The population genetics study was carried out based on seven microsatellite markers which were demonstrated to be polymorphic in this study. This study reported that N. stellenboschiana populations from grapevines and other hosts at three different locations in the Western Cape Province were genetically homogenous. This indicates that there are no barriers which prevent the movement of N. stellenboschiana between grapevines and other hosts. These results are disconcerting because they imply that woody hosts surrounding grapevines which are infected with Botryosphaeriaceae grapevine pathogens could be acting as disease reservoirs and sources of pathogen inoculum which threaten vineyards. To conclude, this study furthered our understanding of the diversity of Botryosphaeriaceae species occurring in woody hosts that commonly surround vineyards in the Western Cape Province of South Africa and described six new species. Furthermore, this study has contributed to our understanding of the epidemiology of these pathogens by demonstrating that the alternative hosts of Botryosphaeriaceae grapevine trunk disease pathogens represent a threat to grapevines by acting as sources of pathogen inoculum. This helps to lay the groundwork for future studies to address this threat by developing improved pathogen management strategies.
- ItemIdentification and characterisation of diatrypaceae species associeated with declining grapevines and alternative hosts in South Africa(Stellenbosch : Stellenbosch University, 2017-03) Moyo, Providence; Halleen, Francois; Lizel Mostert; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Grapevine trunk diseases have devastating impacts on the sustainability of viticulture, worldwide. Eutypa dieback, in particular, has caused large economic losses and premature mortality of vines. This disease has, for many years, been associated with the Diatrypaceae fungus, Eutypa (E.) lata. Several species of Diatrypaceae were, however, recently discovered to be associated with Eutypa dieback-affected grapevines in different grape growing areas including Australia, Chile, Spain and United States of America. No extensive study has been conducted to identify and characterise the species of Diatrypaceae in South Africa. Surveys were conducted in vineyards located in different grape growing regions of the Western Cape and Diatrypaceae fungi were isolated from grapevines with dying spurs or wood with wedge-shaped necrosis in cross section, as well as from perithecia on dead wood. Isolates were studied using phylogenetic analyses of combined DNA sequences of the internal transcribed spacer regions (ITS1 and ITS2) and 5.8S rRNA gene as well as partial β-tubulin gene. Morphological characteristics of perithecia were also studied. Morphological and phylogenetic analyses revealed the presence of seven Diatrypaceae species to occur on grapevine in South Africa, namely Cryptovalsa (C.) ampelina, C. rabenhorstii, E. consobrina, E. lata, Eutypella (Eu.) citricola, Eu. microtheca and E. cremea, which was described as a new species. The most common species isolated from dying spurs, in order of abundance, were C. ampelina (46.4% of total number of isolates), Eu. citricola (26.8%), E. lata (20.1%), E. cremea (4.3%), Eu. microtheca (1.2%), E. consobrina (0.6%) and C. rabenhorstii (0.6%). On the other hand, from wedge-shaped necrosis, E. lata represented the most frequent species (89.2% of all isolates obtained) followed by Eu. citricola (8.5%), E. cremea (1.4%) and C. ampelina (0.9%). Five species namely, E. lata, C. ampelina, E. cremea, Eu. citricola and Eu. microtheca were found to produce perithecia on dead grapevine wood. These results suggest that Eutypa dieback in South Africa can be associated with several Diatrypaceae species. Different fruit and ornamental trees occurring near vineyards were investigated to determine whether they are colonised by Diatrypaceae species, which are associated with Eutypa dieback of grapevine. Isolates of Diatrypaceae were collected from these trees showing symptoms of dieback, cankers and perithecia. Isolates were analysed by morphological and phylogenetic analyses as described above. Fourteen species namely, C. ampelina, E. consobrina, E. lata, Eu. citricola, Eu. microtheca, E. cremea, Cryptosphaeria (Cr.) multicontinentalis, Cr. ligniota, Diatrypella sp., Eu. leprosa, Eu. australiensis and three undescribed Eutypella species were identified from 29 different fruit and ornamental trees, occurring in close proximity to vineyards. The five most prevalent species were E. lata, C. ampelina, E. cremea, Eu. citricola and Eu. microtheca, which were also the most prevalent on grapevine. These findings suggest that cross infections are possibly occurring between grapevine and other woody hosts growing near vineyards in South Africa. These five species were also the only Diatrypaceae species isolated from stone fruit trees. Pathogenicity of these five Diatrypaceae species on stone fruit trees (apricot and plum) was also determined. In these pathogenicity studies, all five species were pathogenic on both apricot and plum, producing brown-red discolouration, typical of Eutypa dieback of apricot. Finally, pathogenicity of Diatrypaceae species identified from grapevine and other woody hosts in South Africa was evaluated on grapevine, under field conditions. Artificial inoculations of these fungal species were conducted on fresh pruning wounds and lignified shoots of Cabernet Sauvignon as well as green shoots of Cabernet Sauvignon and Sauvignon blanc. After 10 months, all the species caused disease symptoms (brown discolouration) on pruning wounds and lignified shoots of Cabernet Sauvignon. Disease symptoms were also observed on green shoots of both cultivars. Pathogenicity results revealed that several species including C. ampelina, Eu. microtheca, Eu. leprosa, and Eu. citricola were equally virulent as the well-known pathogen, E. lata. Quantitative real-time PCR (qPCR) assays were also developed for the detection and quantification of E. lata and C. ampelina in grapevine wood. The qPCR assays were specific and successfully quantified target taxa in artificially inoculated wood samples. The present study provides knowledge on the identity of Diatrypaceae species associated with declining grapevines and other woody hosts occurring adjacent to vineyards in South Africa. This knowledge, together with qPCR assays can be useful in early diagnosis of infection caused by Diatrypaceae species in vineyards. Furthermore, pathogenicity studies have shown that many Diatrypaceae species, including those obtained from other woody hosts, are pathogenic to grapevine. As such, this study forms the platform for further studies aimed at managing Diatrypaceae species causing disease on grapevine in South Africa.
- ItemImproving pruning wound protection against grapevine trunk disease pathogens(Stellenbosch : Stellenbosch University, 2014-03) Mutawila, Cheusi; Mostert, Lizel; Halleen, Francois; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Grapevine trunk diseases are a cause of decline and loss of productivity in grapevines at all stages of growth. These diseases are caused by a complex of wood-inhabiting fungi that infect mainly through pruning wounds. The management of these diseases relies on wound protection to prevent infection since there are no eradicative control measures to cure infected vines. There are few or no fungicides registered for grapevine pruning wound protection in most countries, while Trichoderma biocontrol agents are often available. This study aimed at improving grapevine wound protection by Trichoderma (T.) spp. and to gain a better understanding of the factors and mechanisms involved in biocontrol. The effect of pruning time (early or late) and five timings of application of the biocontrol agent after pruning on pruning wound colonisation by T. atroviride and T. harzianum were determined. Chenin blanc and Cabernet Sauvignon vineyards were pruned in July (early) and August (late) of 2011 and 2012, and pruning wounds were treated with suspensions of the Trichoderma spp. at various times (0, 6, 24, 48 and 96 hours) after pruning. Wound colonisation was depended on the physiological state of the vine at pruning for both cultivars. However, for the 2012 season in Chenin blanc, wound colonisation was similarly high for both pruning times, which was attributed to high rainfall and humidity. Application of the biocontrol agents 6 hours after pruning consistently resulted in high wound colonisation by the Trichoderma spp. in both cultivars and pruning times. In both cultivars, pruning wound infection due to natural inoculum was higher in wounds made in late winter than those made earlier. The effect of conidial formulation in nutritional (glucose, yeast extract and urea) and bio-enhancing (chitin and cell free culture filtrates) additives, on pruning wound colonisation by T. atroviride was also investigated. Nutritional additives increased the extent of pruning wound colonisation by T. atroviride compared to the un-amended conidial suspensions in a glass house study. The additives as well as Garrison, a fungicide containing pruning wound paint, and Eco77®, a registered T. harzianum biocontrol product, were tested in field trials for wound protection from infection by Phaeomoniella (Pa.) chlamydospora. In 2011, the pathogen was inoculated a day after pruning and all the Trichoderma spp. treatments similarly reduced Pa. chlamydospora infection by 75% to 90% in Thompson Seedless, while control was less in Chenin blanc and ranged from 40% to 74%. In 2012, the trial was carried out on Chenin blanc only and the pathogen was inoculated at intervals of 1, 3 and 7 days after pruning. Wound protection by the Trichoderma treatments was highest when wounds were inoculated with Pa. chlamydospora seven days after pruning. Two conidial formulations, a culture filtrate made from a chitin based medium and a combination of yeast extract, urea and glucose, consistently enhanced biocontrol efficacy. These formulations reduced Pa. chlamydospora infection to levels similar to those of Garrison. The integration of chemical and biological wound protection could provide both immediate and long term wound protection, but is limited by the sensitivity of the biocontrol agent to fungicides. Benzimidazole resistant Trichoderma strains were generated by gamma irradiation from the wild type isolates of T. atroviride (UST1 and UST2) and T. harzianum (T77). Mutants from UST1 and UST2 were of similar biological fitness as the wild type isolates and retained their in vitro antagonistic activity against grapevine trunk pathogens, while the mutant from T77 had reduced fitness and was not antagonistic to the pathogens. The wild type, UST1, and its mutant were tested alone and in combination with thiophanate methyl and carbendazim, respectively, for their ability to prevent pruning wound infection by Pa. chlamydospora. The combination of the UST1 mutant and carbendazim was the most effective treatment and gave the highest reduction in Pa. chlamydospora infection (70% to 93% control). Grapevine cell cultures were used to compare the response of grapevines to T. atroviride and Eutypa (E.) lata as a first step to determining the importance of Trichoderma-grapevine interactions in pruning wound bio-protection. The expression of genes coding for enzymes of the phenylpropanoid pathway and pathogenesis related (PR) proteins was profiled over a 48-hour period using quantitative reverse transcriptase PCR. The cell cultures responded to fungal elicitors in a hypersensitive-like response that lead to a decrease in cell viability. Fungal elicitors from both fungi triggered the same genes and caused up-regulation of phenylalanine ammonia-lyase (PAL), 4 coumaroyl Co-A ligase (CCo-A), stilbene synthase (STS), chitinase class IV (CHIT IV), PR 3 and PR 4, and a down regulation of chalcone synthase (CHS) genes. Higher expression of PAL and CHIT IV in cell cultures treated with the T. atroviride elicitor led to a significantly higher (P < 0.05) total phenolic content and chitinolytic enzyme activity of the cell cultures compared to cell cultures treated with the E. lata elicitor. The response of the cell cultures to the T. atroviride elicitor signifies that the induction of grapevine resistance may be involved in wound bio-protection. The role of secondary metabolites produced by Trichoderma spp. used in pruning wound protection was also investigated. A volatile antimicrobial compound, 6-pentyl α-pyrone (6PP), was isolated and found to be the major secondary metabolite from the T. atroviride (UST1 and UST2) and T. harzianum (T77) isolates. This metabolite was found to inhibit mycelial growth, spore and conidia germination of E. lata, Neofussicocum (N.) australe, N. parvum and Pa. chlamydospora. The production of 6PP was induced when the T. atroviride isolates were grown in a grapevine wood extract medium while for UST1, the 6PP concentration was further doubled when it was co-cultured with N. parvum. Results therefore, indicate that 6PP is involved in the Trichoderma-pathogen interactions on pruning wounds. The results of this study have provided new information in regards to the application of Trichoderma-based pruning wound products. The best time of application proved to be 6 hours post pruning. The formulation of conidial suspensions of Trichoderma spp. with nutritional additives and in protein extracts of the biocontrol agent showed potential in reducing variability of wound bio-protection. However, further research would be necessary to develop commercial products. The application of a fungicide together with Trichoderma spp. in the field holds promise to improve control, but would require further trials for possible commercialisation. This study is the first to report on grapevine host defence genes that are activated by the Trichoderma spp. used in pruning wound protection. Together with the characterisation of the major secondary metabolite produced by these Trichoderma spp., this information aids in understanding the mechanisms involved in the complex interaction between the biocontrol agent, the host and the pathogen.
- ItemInoculum ecology of petri disease fungi in grapevines of South Africa(Stellenbosch : Stellenbosch University, 2016-12) Baloyi, Mahlatse Annabella; Halleen, Francois; Mostert, Lizel; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Petri disease is among the important grapevine trunk diseases affecting lifespan and productivity of young vines worldwide. Infection result in poor vine stand in newly established vineyards and a general vine decline. Pathogens causing this disease are known invaders of susceptible pruning wounds. The knowledge of when aerial spore inoculum of these pathogens are released in vineyards has not been reported in South Africa, and this result in growers pruning without the knowledge of whether that would coincide with periods of high aerial spore concentration. This study aimed at investigating when aerial spores of Petri disease pathogens are released, and to determine their source of inoculum. Knowledge regarding spore release in South African vineyards was determined for two seasons in 2012 and 2013. Spore traps were affixed to arms of infected vines in six vineyards and two rootstock mother blocks. Results showed the occurrence of Petri disease pathogens throughout the year and Phaeomoniella chlamydospora and Pm. minimum were trapped in all vineyards. A total of 14 Phaeoacremonium species were identified from the different blocks. Spore release was shown to coincide with pruning and suckering activities, however, there was no positive correlation between rainfall and spore release events. The occurrence of Petri disease pathogens fruiting bodies was determined by surveying six vineyards and two rootstock mother blocks between 2012 and 2014. Dead wood from diseased vines were collected for microscopic examination. Phaeomoniella chlamydospora pycnidia were found in all vineyards and rootstock mother blocks surveyed. Perithecia of Pm. minimum were only found in vineyards of Stellenbosch P2 and B3, Rawsonville and a rootstock mother block in Slanghoek. Additionally, mating studies with isolates of Pm. australiense and Pm. scolyti were conducted in vitro. After seven and eleven months fertile perithecia of Pm. australiense and Pm. scolyti were observed, respectively. Crosses of both species corresponded to a heterothallic mating system. This study gives the first report of the occurrence of pycnidia of Pa. chlamydospora and perithecia of Pm. minimum in South African vineyards and rootstock mother blocks and also the first description of sexual morphs of Pm. australiense and Pm. scolyti. The pathogenic status of 10 Phaeoacremonium species found in South African vineyards was studied. Fresh pruning wounds of a nine-year-old Cabernet Sauvignon vineyard were inoculated with 104 conidia/ml of each fungus per wound and assessed after 18 months. All inoculated isolates successfully colonized pruning wounds causing lesions significantly different from the negative control and were re-isolated at varying percentages ranging from 28.57% to 85.71%. The study confirmed the capability of all tested Phaeoacremonium species to infect grapevine pruning wounds and cause lesions. The genetic diversity and mode of reproduction were assessed using microsatellite markers and also by determining the mating type distribution of aerial trapped spores of Pm. minimum. In total 320 Pm. minimum isolates were assessed with Mat1-2 specific-primers. Both mating types of Pm. minimum were found in all eight vineyards. An equal distribution of MAT1-1 and MAT1-2 were found in six of the vineyards, but not in the Paarl A and Wellington populations. Primers for dinucleotide microsatellite loci were designed and 15 microsatellite loci were identified to be polymorphic and could thus be used to assess the genetic diversity of the Pm. minimum isolates. A total of 134 multilocus genotypes (MLGs) were observed of which 115 were observed once and 19 genotypes were observed either two or more times. The presence of the same MLG in a vineyard at different collection times, supports the presence of asexual reproduction, and the widespread distribution of MLGs is most probably due to infected nursery planting material. The total gene diversity (H) was high with a mean of 0.58 across all populations. Analysis of molecular variance indicated that 94% of the genetic variation was distributed within populations and only 6% between populations. High and significant population differentiation values were only obtained when Paarl Z was compared to Stellenbosch P2. This study confirms the importance of infected planting material that can distribute similar MLGs over long distances. Therefore, the management of Petri disease needs to focus on ensuring clean mother vines and nursery plants.