Research

Research Focus Areas

Pathogen identification and detection
Integrated disease management (including the optimisation of fungicide application)
Post-harvest pathology of fruit crops
In-field management of mycotoxin production in grain crops
Plant-microbe (beneficial and detrimental) interactions

Research Expertise Areas

Grapevine trunk diseases
Spray technology on citrus and grapevines
Oomycete characterisation and detection
Fusarium wilt of banana

Research Programmes
 Fusarium research
Fruit and post-harvest pathology
Grapevine pathology
Citrus pathology
Oomycete research

 

Publications
Departmental list of all publications
Publication list of past 3 years

Research Programmes

Fusarium research (Prof Altus Viljoen)

Plant pathogens belonging to the fungal species Fusarium are of great importance to continued food production in the world. They are well known to cause diseases of important staple food crops such as maize, wheat, sorghum, rice and bananas, and in some instances produce mycotoxins that can be fatal to humans and animals. Many diseases caused by Fusarium spp. and their toxins cannot be treated, and have to be prevented. The programme on Fusarium diseases of agricultural crops, therefore, focuses on the characterisation and management of Fusarium spp. associated with Fusarium wilt and mycotoxin production in staple food crops, specifically related to the identification and characterisation of Fusarium spp. using conventional and molecular techniques, quantitative detection of Fusarium spp. and their mycotoxins, epidemiology and etiology of Fusarium spp., field management of Fusarium diseases and the mycotoxins they produce, biological control of pathogenic Fusarium isolates, and understanding the interaction of plants with Fusarium.
The most effective means to prevent damage caused by Fusarium spp. to agricultural crops is by planting tolerant or resistant material. Such tolerance/resistance depends on the ability of the fungus to enter, colonise and damage the plant, and the ability of the plant to prevent or resist damage caused by the fungus. To exploit plant resistance as a means of disease management, a proper knowledge of Fusarium, its genetics, pathogenicity and toxicity, under different environmental conditions, is required. In this programme, the interaction between agricultural crops and Fusarium spp. is investigated by means of comparative and functional genetics of the Fusarium-plant interactions, the isolation and identification of defence-related genes in agricultural crops, the identification of virulence genes in Fusarium, studies on the evolutionary biology and phylogenetics of Fusarium, and the unconventional improvement of plants for resistance to Fusarium spp. Greenhouse and field evaluation of natural and induced resistance to Fusarium pathogens of agricultural crops are also conducted in collaboration with the ARC.


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Fruit and post-harvest pathology (Dr Cheryl Lennox)

Plant disease and decay impacts on the profitability of deciduous fruit production, and negatively influences consumer confidence in the products. There is an increasing demand from consumers, and consequently retailers and marketers, for fruit with little or no pesticide/fungicide residues. Producing quality fruit under these constraints is a major challenge for the deciduous fruit industry, which currently relies heavily on pre and postharvest chemicals for disease and decay control. The main objective of the Fruit and Postharvest Pathology Research Programme within the department, is to improve disease and decay control in deciduous fruit products, through the design of appropriate integrated disease management strategies, with reduced reliance on fungicides.
Projects within this programme are: Postharvest decay of pears, with focus decay caused by Botrytis cinerea; etiology and epidemiology of core rot of apples; etiology and epidemiology of bull’s eye rot of apples; the efficacy of sanitation practices in reducing apple scab; and the occurrence and importance of overwintering of apple scab conidia in the Western Cape.


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Grapevine pathology (Dr Lizel Mostert)

The field of phytomycology entails the study of fungal systematics and taxonomy of fungal plant pathogens. This knowledge enables the correct identification of causal agents of diseases. The etiology of plant diseases is very important as the first step in understanding the disease aiding in working towards a control strategy. Plant diseases are often complex, being caused by a variety of fungal taxa. The identification and relevance of these taxa are very important. A focus area of research includes the etiology and epidemiology of trunk diseases of grapevine, pome and stone fruit trees.
Phytomycology also entails the development and use of up-to-date molecular identification tools for fungal pathogens that can be used to ensure clean planting material and for early disease warning. The compiling of reliable information regarding the status of fungal pathogens within South Africa is very important. This, together with expertise in phytomycology, is of the utmost importance in order to ensure market access within the agriculture sector, as well as food security in South Africa. Phytosanitary support is provided on an ongoing basis to the deciduous fruit industry (DFPT).
The biological control of plant diseases is important in providing an alternative to chemical control. It allows producers to limit fungicide residues which are becoming an important market requirement. The biocontrol programme focuses on the use of Trichoderma species in the control of grapevine trunk diseases. Various aspects are being researched to understand the mechanisms involved and to optimise the application. These include the formulation, time of application, secondary metabolites produced by the Trichoderma strains, and the host-Trichoderma interactions. Two isolates occurring naturally in grapevines have been tested in vitro and in vivo and is in the process of developing a product that can be used as a pruning wound protectant.


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Citrus pathology (Dr Paul Fourie)

Fungicide application technology

In plant disease control, the use of very effective aqueous remedies (i.e. fungicides, biocontrol agents, GRAS chemicals, etc.) sometimes yield disappointing results whereby growers suffer economic losses. In these cases, disease control failure is often attributed to insufficient application of the remedy. In this research programme, various conventional and novel application technologies are evaluated and optimised in citrus orchards and packhouses in order to ensure biologically effective residue loading onto susceptible plant parts, without exceeding allowable maximum residue levels. Concomitant aims involve addressing cost and time efficiency aspects of application methods, whereby production and environmental costs are directly influenced. The methodology employed involves a proprietary deposition assessment protocol using fluorometry, digital photography and image analyses, as well as residue analysis and biological efficacy tests.

Epidemiology of Citrus Black Spot

Citrus Black Spot (CBS) is a cosmetic disease of citrus fruit. However, its causal organism, Guignardia citricarpa, is regarded as a quarantine organism in certain countries. The South African citrus industry is the second largest exporter of fresh citrus fruit in the world, and therefore CBS is an economically important disease given the market access implications it poses. In this research programme at USPP, the epidemiology of this disease is studied to understand and predict its behaviour under climatically diverse conditions. This will allow improved control programmes, but will also assist in ongoing market access deliberations. Additionally, population genetics of G. citricarpa will be studied on a global scale in order to ascertain the global movement of this organism and the relative importance of sexual and asexual reproduction under diverse climates.

Oomycete research (Dr Adele McLeod)

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Publications

Publication list of past 3 years

  1. Blomme, G., Ploetz, R., Jones, D., De Langhe, E., Price, N., Gold, C., Geering, A., Viljoen, A., Karamura, D., Pillay, M., Tinzaara, W., Teycheney, P.-Y., Lepoint, P., Karamura, E. & Buddenhagen, I. 2013. A historical overview of the appearance and spread of Musa pests and pathogens on the African continent: highlighting the importance of clean Musa planting materials and quarantine measures. Annals of Applied Biology 162: 4-26.
  2. Erasmus, A., Lennox, C.L., Smilanick, J.L., Lesar, K. & Fourie, P.H. 2013. Imazalil residue loading and green mould control on citrus fruit as affected by formulation, solution pH and exposure time in aqueous dip treatments. Postharvest Biology and Technology 77: 43-49.
  3. Fourie, P., Schutte, T., Serfontein, S. & Swart, F. 2013. Modeling the effect of temperature and wetness on Guignardia pseudothecium maturation and ascospore release in citrus orchards. Phytopathology 103: 281-292.
  4. Fry, W.E., McGrath, M.T., Seaman, A., Zitter, T.A., McLeod, A., Danies, G., Small, I.M., Myers, K., Everts, K., Gevens, A.J., Gugino, B.K., Johnson, S.B., Judelson, H., Ristaino, J., Roberts, P., Secor, G., Seebold Jr., K., Snover-Clift, K., Wyenandt, A., Grünwald, N.J. & Smart, C.D. 2013. The 2009 late blight pandemic in the Eastern United States – causes and results. Plant Disease 97: 296-306.
  5. Geiser, D.M., Aoki, T., Bacon, C.W., Baker, S.E., Bhattacharyya, M.K., Brandt, M.E., Brown, D.W., Burgess, L.W., Chulze, S., Coleman, J.J., Correll, J.C., Covert, S.F., Crous, P.W., Cuomo, C.A., De Hoog, G.S., Di Pietro, A., Elmer, W.H., Epstein, L., Frandsen, R.J.N., Freeman, S., Gagkaeva, T., Glenn, A.E., Gordon, T.R., Gregory, N.F., Hammond-Kosack, K.E., Hanson, L.E., del Mar Jímenez-Gasco, M., Kang, S., Kistler, H.C., Kuldau, G.A., Leslie, J.F., Logrieco, A., Lu, G., Lysøe, E., Ma, L-J., McCormick, S.P., Migheli, Q., Moretti, A., Munaut, F., O’Donnell, K., Pfenning, L., Ploetz, R.C., Proctor, R.H., Rehner, S.A., Robert, V.A.R.G., Rooney, A.P., bin Salleh, B., Scandiani, M.M., Scauflaire, J., Short, D.P.G., Steenkamp, E., Suga, H., Summerell, B.A., Sutton, D.A., Thrane, U., Trail, F., Van Diepeningen, A., VanEtten, H.D., Viljoen, A., Waalwijk, C., Ward, T.J., Wingfield, M.J., Xu, J-R., Yang, X-B, Yli-Mattila, T. & Zhang, N. 2013. One fungus, one name: defining the genus Fusarium in a scientifically robust way that preserves longstanding use. Phytopathology 103: 400-408.
  6. Njombolwana, N.S., Erasmus, A. & Fourie, P.H. 2013. Evaluation of curative and protective control of Penicillium digitatum following imazalil application in wax coating. Postharvest Biology and Technology 77: 102-110.
  7. Paparu, P., Dubois, T., Coyne, D. & Viljoen, A. 2013. Differential gene expression in East Africa highland bananas (Musa spp.): Interactions between non-pathogenic Fusarium oxysporum V5w2 and Radopholus similis. Physiological and Molecular Plant Pathology 82: 56-63.
  8. Pule, B.B., Meitz, J.C., Thompson, A.H., Linde, C.C., Fry, W.E., Langenhoven, S.D., Meyers, K.L., Kandolo, D.S., van Rij, N.C. & McLeod, A. 2013. Phytophthora infestans populations in central, eastern and southern African countries consist of two major clonal lineages. Plant Pathology 62: 154-165.
  9. Sutherland, R., Viljoen, A., Myburg, A.A. & Van den Berg, N. 2013. Pathogenicity associated genes in Fusarium oxysporum f. sp. cubense race 4. South African Journal of Science 109 (5/6): 1-10.
  10. Van Zyl, J. Gideon, Fourie, Paul H. & Schutte, Gerhardus C. 2013. Spray deposition assessment and benchmarks for control of Alternaria brown spot on mandarin leaves with copper oxychloride. Crop Protection 46: 80-87.
  11. Wessels, B.A., Lamprecht, S.C., Linde, C.C., Fourie, P.H. & Mostert, L. 2013. Characterization of the genetic variation and fungicide resistance in Botrytis cinerea populations on rooibos seedlings in the Western Cape of South Africa. European Journal of Plant Pathology 136: 407-417.
  12. Boutigny, A.-L., Beukes, I., Small, I., Zühlke, S., Spiteller, M., Van Rensburg, B.J., Flett, B. & Viljoen, A. 2012. Quantitative detection of Fusarium pathogens and their mycotoxins in South African maise. Plant Pathology 61: 522-531.
  13. Carstens, E., Le Roux, H.F., Holtzhausen, M.A., Van Rooyen, L., Coetzee, J., Wentzel, R., Laubscher, W., Dawood, Z., Venter, E., Schutte, G.C., Fourie, P.H. & Hattingh, V. 2012. Citrus black spot is absent in the Western Cape, Northern Cape and Free State Provinces. South African Journal of Science 108 (7/8): 1-6.
  14. Gouws, R. & McLeod, A. 2012. Fissure scab, a new symptom associated with potato common scab caused by a Streptomyces sp. in South Africa. Plant Disease 96: 1223.
  15. Gramaje, D., Agusti-Brisach, C., Pérez-Sierra, A., Moralejo, E., Olmo, D., Mostert, L., Damm, U. & Armengol, J. 2012. Fungal trunk pathogens associated with wood decay of almond trees on Mallorca (Spain). Persoonia 28: 1-13.
  16. Hu, C.-H., Perez, F.G., Donahoo, R., McLeod, A., Myers, K., Ivors, K., Secor, G., Roberts, P.D., Deahl, K.L., Fry, W.E. & Ristaino, J.B. 2012. Recent genotypes of Phytophthora infestans in the Eastern United States reveal clonal populations and reappearance of mefenoxam sensitivity. Plant Disease 96: 1323-1330.
  17. Schutte, G.C., Kotze, C., van Zyl, J.G. & Fourie, P.H. 2012. Assessment of retention and persistence of copper fungicides on orange fruit and leaves using fluorometry and copper residue analyses. Crop Protection 42: 1-9.
  18. Small, I.M., Flett, B.C., Marasas, W.F.O., McLeod, A., Stander, M.A. & Viljoen, A. 2012. Resistance in maize inbred lines to Fusarium verticillioides and fumonisin accumulation in South Africa. Plant Disease 96: 881-888.
  19. Small, I.M., Flett, B.C., Marasas, W.F.O., McLeod, A. & Viljoen, A. 2012. Use of resistance elicitors to reduce Fusarium ear rot and fumonisin accumulation in maize. Crop Protection 41: 10-16.
  20. Southwood, M.J., Viljoen, A., Mostert, G. & McLeod, A. 2012. Molecular identification of two vegetative compatibility groups of Fusarium oxysporum f.sp. cepae. Phytopathology 102: 204-213.
  21. Southwood, M.J., Viljoen, A., Mostert, L., Rose, L.J. & McLeod, A. 2012. Phylogenetic and biological characterization of Fusarium oxysporum isolates associated with onion in South Africa. Plant Disease 96 (9): 1250-1261.
  22. Van Wyk, S.J.P., Boutigny, A.-L., Coutinho, T.A. & Viljoen, A. 2012. Sanitation of a South African forestry nursery contaminated with Fusarium circinatum using hydrogen peroxide at specific oxidation reduction potentials. Plant Disease 96: 875-880.
  23. Belgrove, A., Steinberg, C. & Viljoen, A. 2011. Evaluation of nonpathogenic Fusarium oxysporum and Pseudomonas fluorescens for Panama disease control. Plant Disease 95: 951-959.
  24. Boutigny, A.-L., Beukes, I. & Viljoen, A. 2011. Head blight of barley in South Africa is caused by Fusarium graminearum with a 15-adon chemotype. Journal of Plant Pathology 93 (2): 321-329.
  25. Boutigny, A.-L., Ward, T.J., van Coller, G.J., Flett, B., Lamprecht, S.C., O’Donnell, K. & Viljoen, A. 2011. Analysis of the Fusarium graminearum species complex from wheat, barley and maize in South Africa provides evidence of species-specific differences in host preference. Fungal Genetics and Biology 48: 914-920.
  26. Cloete, M., Fourie, P.H., Damm, U., Crous, P.W. & Mostert, L. 2011. Fungi associated with die-back symptoms of apple and pear trees, a possible inoculum source of grapevine trunk disease pathogens. Phytopathologia Mediterranea 50 (Supplement): S176-S190.
  27. Crous, P.W., Summerell, B.A., Swart, L., Denman, S., Taylor, J.E., Bezuidenhout, C.M., Palm, M.E., Marincowitz, S. & Groenewald, J.Z. 2011. Fungal pathogens of Proteaceae. Persoonia 27: 20-45.
  28. Erasmus, A., Lennox, C.L., Jordaan, H., Smilanick, J.L., Lesar, K. & Fourie, P.H. 2011. Imazalil residue loading and green mould control in citrus packhouses. Postharvest Biology and Technology 62: 193-203.
  29. Fourie, G., Steenkamp, E.T., Ploetz, R.C., Gordon, T.R. & Viljoen, A. 2011. Current status of the taxonomic position of Fusarium oxysporum formae specialis cubense within the Fusarium oxysporum complex. Infection, Genetics and Evolution 11: 533-542.
  30. Gramaje, D., Mostert, L. & Armengol, J. 2011. Characterization of Cadophora luteo-olivacea and C. melinii isolates obtained from grapevines and environmental samples from grapevine nurseries in Spain. Phytopathologia Mediterranea 50 (Supplement): S112-S126.
  31. Kotze, C., Van Niekerk, J., Mostert, L. Halleen, F. & Fourie, P. 2011. Evaluation of biocontrol agents for grapevine pruning wound protection against trunk pathogen infection. Phytopathologia Mediterranea 50 (Supplement): S247-S263.
  32. Mutawila, C., Fourie, P.H., Halleen, F. & Mostert, L. 2011. Grapevine cultivar variation to pruning wound protection by Trichoderma species against trunk pathogens. Phytopathologia Mediterranea 50 (Supplement): S264-S276.
  33. Mutawila, C., Fourie, P.H., Halleen, F. & Mostert, L. 2011. Histo-pathology study of the growth of Trichoderma harzianum, Phaeomoniella chlamydospora and Eutypa lata on grapevine pruning wounds. Phytopathologia Mediterranea 50 (Supplement): S46-S60.
  34. Ncube, E., Flett, B.C., Waalwijk, C. & Viljoen, A. 2011. Fusarium spp. and levels of fumonisins in maize produced by subsistence farmers in South Africa. South African Journal of Science 107 (1/2): 1-7.
  35. Spies, C.F.J., Mazzola, M., Botha, W.J., Langenhoven, S.D., Mostert, L. & McLeod, A. 2011. Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species. Fungal Biology 115: 1210-1224.
  36. Spies, C.F.J., Mazzola, M., Botha, W.J., Van der Rijst, M., Mostert, L. & McLeod, A. 2011. Oogonial biometry and phylogenetic analyses of the Pythium vexans species group from woody agricultural hosts in South Africa reveal distinct groups within this taxon. Fungal Biology 115: 157-168.
  37. Spies, C.F.J., Mazzola, M. & McLeod, A. 2011. Characterisation and detection of Pythium and Phytophthora species associated with grapevines in South Africa. European Journal of Plant Pathology 131: 103-119.
  38. Tesfai Tewoldemedhin, Y., Mazzola, M., Botha, W.J., Spies, C.F.J. & McLeod, A. 2011. Characterization of fungi (Fusarium and Rhizoctonia) and oomycetes (Phytophthora and Pythium) associated with apple orchards in South Africa. European Journal of Plant Pathology 130: 215-229.
  39. Tesfai Tewoldemehin, Y., Mazzola, M., Labuschagne, I. & McLeod, A. 2011. A multi-phasic approach reveals that apple replant disease is caused by multiple biological agents, with some agents acting synergistically. Soil Biology & Biochemistry 43: 1917-1927.
  40. Tesfai Tewoldemedhin, Y., Mazzola, M, Mostert, L. & McLeod, A. 2011. Cylindrocarpon species associated with apple tree roots in South Africa and their quantification using real-time PCR. European Journal of Plant Pathology 129: 637-651.
  41. Van der Walt, L., Spotts, R.A., Ueckermann, E.A., Smit, F.J., Jensen, T. & McLeod, A. 2011. The association of Tarsonemus mites (Acari: Heterostigmata) with different apple developmental stages and apple core rot diseases. International Journal of Acarology 37: Suppl. 1: 71-84.
  42. Van Niekerk, J.M., Bester, W., Halleen, F., Crous, P.W. & Fourie, P.H. 2011. The distribution and symptomatology of grapevine trunk disease pathogens are influenced by climate. Phytopathologia Mediterranea 50 (Supplement): S98-S111.
  43. Van Niekerk, J.M. Halleen, F. & Fourie, P.H. 2011. Temporal susceptibility of grapevine pruning wounds to trunk pathogen infection in Souht African grapevines. Phytopathologia Mediterranea 50 (Supplement): S139-S150.
  44. Van Niekerk, J.M., Strever, A.E., du Toit, P.G., Halleen, F. & Fourie, P.H. 2011. Influence of water stress on Botryosphaeriaceae disease expression in grapevines. Phytopathologia Mediterranea 50 (Supplement): S151-S165.
  45. White, C-L. Halleen, F., Fischer, M. & Mostert, L. 2011. Characterisation of the fungi associated with esca diseased grapevines in South Africa. Phytopathologia Mediterranea 50: 204-223.
  46. Bezuidenhout, C.M., Denman, S., Kirk, S.A., Botha, W.J., Mostert, L. & McLeod, A. 2010. Phytophthora taxa associated with cultivated Agathosma, with emphasis on the P. citricola complex and P. capensis sp. nov. Persoonia 25: 32-49.
  47. Bonants, P., Groenewald, E., Rasplus, J.Y., Maes, M., de Vos, P., Frey, J., Boonham, N., Nicolaisen, M., Bertacini, A., Robert, V., Barker, I., Kox, L., Ravnikar, M., Tomankova, K., Caffier, D., Li, M., Armstrong, K., Freitas-Astúa, J., Stefani, E., Cubero, J. & Mostert, L. 2010. QBOL: a new EU project focusing on DNA barcoding of Quarantine organisms. Bulletin OEPP/EPPO Bulletin 40: 30-33.
  48. Damm, U., Fourie, P.H. & Crous, P.W. 2010. Coniochaeta (Lecythophora), Collophora gen. nov. and Phaeomoniella species associated with wood necroses of Prunus trees. Persoonia 24: 60-80.
  49. Dunn, A.R., Milgroom, M.G., Meitz, J.C., McLeod, A., Fry, W.E., McGrath, M.T., Dillard, H.R. & Smart, C.D. 2010. Population structure and resistance to mefenoxam of Phytophthora capsici in New York State. Plant Disease 94: 1461-1468.
  50. Kiggundu, A., Muchwezi, J., Van der Vyver, C., Viljoen, A., Vorster, J., Schlüter, U., Kunert, K. & Michaud, D. 2010. Deleterious effects of plant cystatins against the banana weevil Cosmopolites sordidus. Archives of Insect Biochemistry and Physiology 73: 87-105.
  51. Meitz, J.C., Linde, C.C., Thompson, A., Langenhoven, S. & McLeod, A. 2010. Phytophthora capsici on vegetable hosts in South Africa: distribution, host range and genetic diversity. Australasian Plant Pathology 39: 431-439.
  52. Mostert, L., Bester, W., Jensen, T., Coertze, S., Van Hoorn, A., Le Roux, J., Retief, E., Wood, A. & Aime, M.C. 2010. First report of leaf rust of blueberry caused by Thekopsora minima on vaccinium corymbosum in the Western Cape, South Africa. Plant Disease 94: 478.
  53. Ncube, E., Flett, B.C., Waalwijk, C. & Viljoen, A. 2010. Occurrence of aflatoxins and aflatoxin-producing Aspergillus spp. associated with groundnut production in subsistence farming systems in South Africa. South African Journal of Plant & Soil 27 (2): 195-198.
  54. Paparu, P., Dubois, T., Coyne, D. & Viljoen, A. 2010. Effect of Fusarium oxysporum endophyte inoculation on the activities of phenylpropanoid pathway enzymes and Radopholus similis numbers in susceptible and tolerant East African Highland bananas. Nematology 12(3): 469-480.
  55. Van der Walt, L., Spotts, R.A., Visagie, C.M., Jacobs, K, Smit, F.J. & McLeod, A. 2010. Penicillium species associated with preharvest wet core rot in South Africa and their pathogenicity on apple. Plant Disease 94 (6): 666-675.
  56. Van Niekerk, J.M., Calitz, F.J., Halleen, F. & Fourie, P.H. 2010. Temporal spore dispersal patterns of grapevine trunk pathogens in South Africa. European Journal of Plant Pathology 127: 375-390.
  57. Van Zyl, S.A., Brink, J-C., Calitz, F.J., Coertze, S. & Fourie, P.H. 2010. The use of adjuvants to improve spray deposition and Botrytis cinerea control on Chardonnay grapevine leaves. Crop Protection 29: 58-67.
  58. Van Zyl, S.A., Brink, J-C., Calitz, F.J. & Fourie, P.H. 2010. Effects of adjuvants on deposition efficiency of fenhexamid sprays applied to Chardonnay grapevine foliage. Crop Protection 29: 843-852.
  59. Visser, M., Gordon, T., Fourie, G. & Viljoen, A. 2010. Characterisation of South African isolates of Fusarium oxysporum f. sp. cubense from Cavendish bananas. South African Journal of Science 106: 1-6.

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