A multi-phasic approach reveals that apple replant disease is caused by multiple biological agents, with some agents acting synergistically

Simple item page
dc.contributor.authorTewoldemedhin Y.T.
dc.contributor.authorMazzola M.
dc.contributor.authorLabuschagne I.
dc.contributor.authorMcLeod A.
dc.date.accessioned2011-10-13T16:58:11Z
dc.date.available2011-10-13T16:58:11Z
dc.date.issued2011
dc.description.abstractApple replant disease (ARD) has been reported from all major fruit-growing regions of the world, and is often caused by a consortium of biological agents. The aim of this study was to investigate the etiology of ARD in South Africa in six orchard soils, using a multiphasic approach under glasshouse conditions. This approach first involved determining the ARD status of the soils by monitoring apple seedling growth responses in non-treated soil versus growth in pasteurized soil, as well as in 15% non-treated soil that was diluted into pasteurized soil. Subsequently, the potential for specific organisms to function as causal agents of ARD was investigated using (i) biocide applications, (ii) quantitative real-time PCR (qPCR) analyses of ARD 'marker' microbes (Pythium irregulare, Pythium sylvaticum, Pythium ultimum, Pythium vexans, Rhizoctonia solani AG-5 and the genera Cylindrocarpon and Phytophthora), (iii) nematode analyses, (iv) isolation of actinomycetes and (v) pathogenicity testing of actinomycetes individually, and when co-inoculated with P. irregulare or Cylindrocarpon macrodidymum. The analyses showed that the soils could be grouped into low, moderate and severe ARD soils, with each group containing two soils. Several lines of evidence suggested that actinomycetes are not involved in ARD in South Africa. Multiple biological agents were determined to contribute to ARD including (i) oomycetes (Phytophthora and Pythium) that are important based upon their widespread occurrence, and the fact that metalaxyl application improved seedling growth in four soils (ii) the genus Cylindrocarpon that was also widespread, and for which a synergistic interaction with P. irregulare was demonstrated and (iii) occasionally parasitic nematodes, mainly Pratylenchus penetrans, Pratylenchus scribneri and Pratylenchus delattrei, since fenamiphos application improved seedling growth in two orchards. qPCR analyses of the ARD marker microbes showed that R. solani AG-5 is absent from South African orchards, and that P. ultimum is widespread, even though the latter species could not be detected in previous isolation studies. The other marker microbes were also widespread, with the exception of P. sylvaticum. qPCR quantification of the marker microbes could not be correlated with the severity of ARD in any manner. qPCR analyses did, however, show that possible root pruning pathogens such as P. irregulare, P. sylvaticum and P. ultimum had much lower DNA concentrations in seedling roots than P. vexans and the genera Cylindrocarpon and Phytophthora. © 2011 Elsevier Ltd.
dc.description.versionArticle
dc.identifier.citationSoil Biology and Biochemistry
dc.identifier.citation43
dc.identifier.citation9
dc.identifier.citationhttp://www.scopus.com/inward/record.url?eid=2-s2.0-80051470662&partnerID=40&md5=5ca23f02f358d3d1a6ffb83a2cf12474
dc.identifier.issn380717
dc.identifier.other10.1016/j.soilbio.2011.05.014
dc.identifier.urihttp://hdl.handle.net/10019.1/16640
dc.subjectActinomycetes
dc.subjectApple replant disease
dc.subjectFungi
dc.subjectNematode
dc.subjectOomycetes
dc.subjectReal time PCR
dc.subjectRoot pathogen quantification
dc.subjectActinomycetes
dc.subjectApple replant disease
dc.subjectNematode
dc.subjectOomycetes
dc.subjectReal-time PCR
dc.subjectRoot pathogen quantification
dc.subjectBacteria
dc.subjectEcology
dc.subjectForestry
dc.subjectFruits
dc.subjectOrchards
dc.subjectPasteurization
dc.subjectPathogens
dc.subjectPlants (botany)
dc.subjectPolymerase chain reaction
dc.subjectSoils
dc.subjectdisease severity
dc.subjectdisease vector
dc.subjectetiology
dc.subjectfruit
dc.subjectfungus
dc.subjectgrowth response
dc.subjectnematode
dc.subjectpathogenicity
dc.subjectpolymerase chain reaction
dc.subjectreal time
dc.subjectsynergism
dc.subjectSouth Africa
dc.subjectActinobacteria
dc.subjectActinobacteria (class)
dc.subjectCylindrocarpon
dc.subjectFungi
dc.subjectHyphomycetes
dc.subjectMalus x domestica
dc.subjectNematoda
dc.subjectNeonectria macrodidyma
dc.subjectOomycetes
dc.subjectPhytophthora
dc.subjectPratylenchus delattrei
dc.subjectPratylenchus penetrans
dc.subjectPratylenchus scribneri
dc.subjectPythium
dc.subjectPythium irregulare
dc.subjectPythium sylvaticum
dc.subjectPythium ultimum
dc.subjectPythium vexans
dc.subjectThanatephorus cucumeris
dc.titleA multi-phasic approach reveals that apple replant disease is caused by multiple biological agents, with some agents acting synergistically
dc.typeArticle
Files
Collections
Stellenbosch University - Scopus Publications