13 research outputs found

    Anastomosis groups and pathogenicity of Rhizoctonia solani and binucleate Rhizoctonia from potatoes in South Africa

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    A survey of anastomosis groups (AGs) of Rhizoctonia species associated with potato diseases was conducted in South Africa. A total of 112 Rhizoctonia solani and 19 binucleate Rhizoctonia (BNR) isolates were recovered from diseased potato plants, characterized for AG and pathogenicity. The AG identity of the isolates was confirmed using phylogenetic analysis of the internal transcribed spacer region of ribosomal DNA. Rhizoctonia solani isolates recovered belonged to AG 3-PT, AG 2- 2IIIB, AG 4HG-I, AG 4HG-III and AG 5, while BNR isolates belonged to AG A and AG R, with frequencies of 74, 6.1, 2.3, 2.3, 0.8, 12.2 and 2.3%, respectively. Rhizoctonia solani AG 3-PT was the most predominant AG and occurred in all the potato growing regions sampled whereas the other AGs occurred in distinct locations. Different AGs grouped into distinct clades with high maximum parsimony and maximum likelihood bootstrap support for both R. solani and BNR. An experiment under greenhouse conditions with representative isolates from different AGs showed differences in aggressiveness between and within AGs. Isolates of AG 2-2IIIB, AG 4HG-III and AG R were the most aggressive in causing stem canker while AG 3-PT, AG 5 and AG R caused black scurf. This is the first comprehensive survey of R. solani and BNR on potatoes in South Africa using a molecularbased approach. This is the first report of R. solani AG 2-2IIIB and AG 4 HG-I causing stem and stolon canker and BNR AG A and AG R causing stem canker and black scurf on potatoes in South Africa.Potatoes South Africa.National Research Foundation of South Africa (UID: 78566 (NRF RISP grant for the ABI3500)).http://apsjournals.apsnet.org/loi/pdishb201

    Population genetic structure of Rhizoctonia solani AG 3-PT from potatoes in South Africa

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    Rhizoctonia solani AG 3-PT is an important potato pathogen causing significant yield and quality losses in potato production globally. However, little is known about the levels of genetic diversity and population structure of this pathogen in South Africa. A total of 114 R. solani AG 3-PT isolates collected from four geographic regions were analyzed for genetic diversity and structure using eight microsatellite loci. Microsatellite analysis found high intrapopulation genetic diversity, population differentiation and evidence of recombination. A total of 78 multilocus genotypes (MLGs) were identified with few MLGs shared among populations. Low levels of clonality (13-39 %) and high levels of population differentiation were observed among populations. Most of the loci were in Hardy-Weinberg equilibrium and all four field populations showed evidence of a mixed reproductive mode of both clonality and recombination. The PCoA clustering method revealed genetically distinct geographic populations of R. solani AG 3-PT in South Africa. This study showed that populations of R. solani AG 3-PT in South Africa are genetically differentiated and disease management strategies should therefore be applied accordingly. This is the first study of the population genetics of R. solani AG 3-PT in potatoes in South Africa and results may help to develop knowledge-based disease management strategies in South Africa and elsewhere.Potatoes South Africa and the Potato Pathology Programme at UP as well as the National Research Foundation.http://www.elsevier.com/locate/funbio2017-05-31hb2016Plant Scienc

    First report of Rhizoctonia solani AG 4HG-III causing potato stem canker in South Africa

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    No abstract available.http://apsjournals.apsnet.org/loi/pdishb201

    Variation in fungicide sensitivity among Rhizoctonia isolates recovered from potatoes in South Africa

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    Please read abstract in the article.Potatoes South Africahttp://apsjournals.apsnet.org/loi/pdishj2018Plant Production and Soil Scienc

    Development of a TaqMan PCR assay for specific detection and quantification of Pectobacterium brasiliense in potato tubers and soil

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    Pectobacterium brasiliense (Pb) is one of the causal agents of soft rot and blackleg diseases and has become a pathogen of economic importance in many potato production regions worldwide. Accurate, sensitive and timely identification of Pb is critical for improved management of the pathogen to mitigate yield losses. This study describes the development and validation of a TaqMan probe-based quantitative real-time PCR assay for rapid and specific detection of Pb in plant material and soil. A primer-pair that amplifies a 125-bp fragment was designed from the 16-23 s intergenic spacer region ribosomal RNA and the tRNA-Glu gene region. The specificity of the assay was evaluated with 24 isolates representative of nine different Pectobacterium and Dickeya species associated with soft rot and blackleg of potatoes. The designed Pb species-specific primers and FAM-labelled TaqMan probe were specific for detection of Pb in all the assays performed and it did not detect other Pectobacterium and Dickeya species. The TaqMan PCR assay could detect Pb DNA quantities as low as 10 fg/µl and DNA from a concentration of cells as low as 103 colony forming units/ml. The assay was capable of identifying and quantifying Pb in potato tubers and in field soils without the interference of inhibitors. The developed TaqMan PCR assay can be used for routine Pb diagnostics, surveillance and epidemiological studies.https://link.springer.com/journal/106582021-08-20hj2020Plant Production and Soil Scienc
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