Journal article
Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species
Fungal biology, Vol.115(12), pp.1210-1224
2011
Handle:
https://hdl.handle.net/2376/101537
PMID: 22115440
Abstract
The
Pythium irregulare species complex is the most common and widespread
Pythium spp. associated with grapevines in South Africa. This species complex has been subdivided into several morphological and phylogenetic species that are all highly similar at the sequence level [internal transcribed spacer (ITS) and cytochrome c oxidase (
cox) regions]. The complex includes
Pythium regulare and
Pythium cylindrosporum, which are morphologically distinct, and
P. irregulare sensu stricto (
s.s.) and
Pythium cryptoirregulare, which are morphologically similar. The aim of the current study was to determine whether 50 South African grapevine
P. irregulare isolates represented more than one phylogenetically distinct species. The isolates were characterised using nuclear (ITS and β-tubulin) and mitochondrial (
cox1 and
cox2) gene region phylogenies and two isozyme loci [glucose-6-phosphate isomerase (
Gpi) and malate dehydrogenase (
Mdh-1)]. Some of the gene sequence data were difficult to interpret phylogenetically, since some isolates contained two or more polymorphic ITS copies within the same isolate (intra-isolate variation) that clustered into different ITS sub-clades, i.e. the
P. irregulare s.s. and
P. cryptoirregulare sub-clades. The molecular data furthermore only revealed the presence of one phylogenetic species,
P. irregulare. Morphological analyses of a subset of the isolates confirmed that the isolates were
P. irregulare, and further showed that the
P. cylindrosporum ex-type strain formed typical
P. irregulare oogonia, and not the previously reported distinct elongated oogonia. Some of the molecular analyses suggested the occurrence of outcrossing events and possibly the formation of aneuploids or polyploids since (i) the nuclear and mitochondrial gene data sets were incongruent, (ii) polymorphic ITS copies were present within the same isolate, (iii) heterozygosities were observed in the β-tubulin gene and
Gpi and
Mdh-1 loci in some isolates and (iv) more than two β-tubulin alleles were detected in some isolates. Altogether, the data suggest that
P. irregulare,
P. cryptoirregulare,
P. cylindrosporum, and possibly
P. regulare should be synonimised under the name
P. irregulare.
► The taxonomy of
Pythium irregulare isolates were investigated. ► Phylogenies indicated this species complex to be a single variable species. ► No morphological differences were observed between isolates. ► Species in this complex should be synonimised. ► Sexual reproduction might be involved in generating diversity.
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Details
- Title
- Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species
- Creators
- Christoffel F.J Spies - Department of Plant Pathology, University of Stellenbosch, Private Bag X1, Matieland 7602, South AfricaMark Mazzola - USDA-ARS, Tree Fruit Research Laboratory, 1104 M. Western Avenue, Wenatchee, WA 98801, USAWilhelm J Botha - ARC PPRI, Private Bag X134, Queenswood, Pretoria 0121, South AfricaShaun D Langenhoven - Department of Plant Pathology, University of Stellenbosch, Private Bag X1, Matieland 7602, South AfricaLizel Mostert - Department of Plant Pathology, University of Stellenbosch, Private Bag X1, Matieland 7602, South AfricaAdéle Mcleod - Department of Plant Pathology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
- Publication Details
- Fungal biology, Vol.115(12), pp.1210-1224
- Academic Unit
- Plant Pathology, Department of
- Publisher
- Elsevier Ltd
- Identifiers
- 99900546533201842
- Language
- English
- Resource Type
- Journal article