Genetic and pathogenic variation among cereal, medic and sub-clover isolates of Pythium irregulare

Harvey, Paul R.; Butterworth, Peter J.; Hawke, Bruce; Pankhurst, C. E.

doi:10.1017/s0953756200002902

Cited by 34 publications

(11 citation statements)

References 30 publications

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“…This is in agreement with the homothallic nature of this pathogen (27) and could have resulted in lower levels of genetic diversity when compared with Pythium populations that reproduce by crossing (16,17).…”

Section: Discussionsupporting

confidence: 87%

Analysis of Diversity inPythium aphanidermatumPopulations from a Single Greenhouse Reveals Phenotypic and Genotypic Changes over 2006 to 2011

et al. 2012

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A study was conducted to investigate phenotypic and genotypic changes within Pythium aphanidermatum populations during the period 2006 to 2011. In total, 92 isolates of P. aphanidermatum (59 in 2006 and 33 in 2011) were obtained from different planting sites (soil) of cucumber from a single greenhouse. Generated sequences of the internal transcribed spacer (ITS) ribosomal DNA showed that all, except one isolate, share an identical sequence of the ITS region. Most (89%) P. aphanidermatum isolates were found to be aggressive on cucumber seedlings, with no significant differences in the aggressiveness level between populations obtained from different planting rows or different years. Sensitivity to metalaxyl among populations of P. aphanidermatum increased significantly from concentration resulting in 50% growth inhibition levels of 0.070 to 1.823 (average 0.824 μg ml–1) in 2006 to 0.002 to 0.564 (average 0.160 μg ml–1) in 2011. Amplified fragment length polymorphism analysis of the 92 isolates produced 92 different genotypes and 985 polymorphic loci. P. aphanidermatum populations from 2006 and 2011 were found to have low levels of genetic diversity (H = 0.1425), which implies introduction of the isolates into the greenhouse via common sources. Results from analysis of molecular variance (FST = 0.0307 in 2006 and 0.0222 in 2011) provided evidence for frequent exchange of Pythium inoculum between different planting locations within the same year. However, the analysis showed moderate levels (FST = 0.1731) of genetic differentiation among populations from the 2 years. This was supported by unweighted pair group method with arithmetic means analysis, which showed clustering of many of the 2006 isolates in separate clusters. The change in the metalaxyl sensitivity of the populations from 2006 to 2011 accompanied by the genetic differences among these two populations may suggest that many of the isolates from 2006 were lost and were replaced by new and highly sensitive P. aphanidermatum isolates by 2011.

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Section: Discussionsupporting

confidence: 87%

Analysis of Diversity inPythium aphanidermatumPopulations from a Single Greenhouse Reveals Phenotypic and Genotypic Changes over 2006 to 2011

et al. 2012

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“…ultimum var. ultimum , Pythium irregulare is a species with globose sporangia, highly virulent at cooler temperatures [10], occurs in a broad eco-geographic range, and exhibits high genetic and morphological diversity [23], [39], [40], [41]. Unlike other species, Pythium vexans , which belongs to clade K and should be renamed as Phytopythium , causes root rot disease in many economically important tropical trees such as durian and rubber plants [42], [43].…”

Section: Introductionmentioning

confidence: 99%

Comparative Genomics Reveals Insight into Virulence Strategies of Plant Pathogenic Oomycetes

et al. 2013

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The kingdom Stramenopile includes diatoms, brown algae, and oomycetes. Plant pathogenic oomycetes, including Phytophthora, Pythium and downy mildew species, cause devastating diseases on a wide range of host species and have a significant impact on agriculture. Here, we report comparative analyses on the genomes of thirteen straminipilous species, including eleven plant pathogenic oomycetes, to explore common features linked to their pathogenic lifestyle. We report the sequencing, assembly, and annotation of six Pythium genomes and comparison with other stramenopiles including photosynthetic diatoms, and other plant pathogenic oomycetes such as Phytophthora species, Hyaloperonospora arabidopsidis, and Pythium ultimum var. ultimum. Novel features of the oomycete genomes include an expansion of genes encoding secreted effectors and plant cell wall degrading enzymes in Phytophthora species and an over-representation of genes involved in proteolytic degradation and signal transduction in Pythium species. A complete lack of classical RxLR effectors was observed in the seven surveyed Pythium genomes along with an overall reduction of pathogenesis-related gene families in H. arabidopsidis. Comparative analyses revealed fewer genes encoding enzymes involved in carbohydrate metabolism in Pythium species and H. arabidopsidis as compared to Phytophthora species, suggesting variation in virulence mechanisms within plant pathogenic oomycete species. Shared features between the oomycetes and diatoms revealed common mechanisms of intracellular signaling and transportation. Our analyses demonstrate the value of comparative genome analyses for exploring the evolution of pathogenesis and survival mechanisms in the oomycetes. The comparative analyses of seven Pythium species with the closely related oomycetes, Phytophthora species and H. arabidopsidis, and distantly related diatoms provide insight into genes that underlie virulence.

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“…The biological species concept has not been used explicitly in investigations of the P. irregulare species complex, but some indications of outcrossing or hybridisation within this species complex (Harvey et al 2000(Harvey et al , 2001Lee & Moorman 2008, current study) suggest that the P. irregulare species complex could be a single biological species. Interspecific hybridisation in the P. irregulare species complex was also supported by our phylogenetic and Southern analyses (see following paragraphs).…”

Section: Discussionmentioning

confidence: 91%

“…It is therefore possible that the genetic variability within the P. irregulare species complex is maintained by a similar process of sexual outcrossing followed by selfing. Some molecular evidence of sexual outcrossing within P. irregulare has been obtained by Harvey et al (2000Harvey et al ( , 2001 and Lee & Moorman (2008) also suggested that hybridisation between P. irregulare and P. cryptoirregulare could have contributed to the genetic diversity of this species complex. Sexual outcrossing within the P. irregulare species complex would also help to explain the incongruence observed between the nuclear and mitochondrial gene regions used in our study, and high levels of heterozygosity that were identified in the b-tubulin gene and Gpi and Mdh-1 loci in some isolates.…”

Section: Discussionmentioning

confidence: 93%

Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species

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Mazzola

Botha³

et al. 2011

Fungal Biology

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Genetic and pathogenic variation among cereal, medic and sub-clover isolates of Pythium irregulare

Cited by 34 publications

References 30 publications

Analysis of Diversity inPythium aphanidermatumPopulations from a Single Greenhouse Reveals Phenotypic and Genotypic Changes over 2006 to 2011

Analysis of Diversity inPythium aphanidermatumPopulations from a Single Greenhouse Reveals Phenotypic and Genotypic Changes over 2006 to 2011

Comparative Genomics Reveals Insight into Virulence Strategies of Plant Pathogenic Oomycetes

Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species

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