Journal article
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, Vol.115(2), pp.157-168
2011
Handle:
https://hdl.handle.net/2376/116386
PMID: 21315313
Abstract
Pythium vexans fits into the internal transcribed spacer (ITS) clade K
sensu
Lévesque & De Cock (2004). Within clade K,
P. vexans forms a distinct clade containing two enigmatic species,
Pythium indigoferae and
Pythium cucurbitacearum of which no ex-type strains are available. In South Africa, as well as in other regions of the world,
P. vexans isolates are known to be heterogeneous in their ITS sequences and may consist of more than one species. This study aimed to investigate the diversity of South African
P. vexans isolates, mainly from grapevines, but also citrus and apple using (i) phylogenetic analyses of the ITS, cytochrome c oxidase (
cox) I,
cox II, and β-tubulin regions and (ii) seven biometric oogonial parameters. Each of the phylogenies clustered
P. vexans isolates into a single well-supported clade, distinct from other clade K species. The β-tubulin region was phylogenetically uninformative regarding the
P. vexans group. The ITS phylogeny and combined
cox I and II phylogenies, although each revealing several
P. vexans subclades, were incongruent. One of the most striking incongruences was the presence of one
cox subclade that contained two distinct ITS subclades (Ib and IV). Three groups (A–C) were subjectively identified among South African
P. vexans isolates using (i) phylogenetic clades (ITS and
cox), (ii) univariate analysis of oogonial diameters, and (iii) multivariate analyses of biometric oogonial parameters. Group A is considered to be
P. vexans s. str. since it contained the
P. vexans CBS reference strain from
Van der Plaats-Niterink (1981). This group had significantly smaller oogonial diameters than group B and C isolates. Group B contained the isolates from ITS subclades Ib and IV, which formed a single
cox subclade. The ITS subclade IV isolates were all sexually sterile or produced mainly abortive oospores, as opposed to the sexually fertile subclade Ib isolates, and may thus represent a distinct assemblage within group B. Although ITS subclade Ib included the
P. indigoferae ex-type sequence, this group was considered to be
P. vexans since South African isolates in this clade produced globose sporangia. Group C contained four apple isolates that were related to, but distinct from
P. cucurbitacearum. Although
P. vexans groups A–C might be distinct species, they are not described here as such due to (i) these groups only representing some of the known diversity in
P. vexans, (ii) conflicting gene tree phylogenies preventing phylogenetic species identification, and (iii) sexually sterile isolates preventing the broad application of biometrical data.
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Details
- Title
- Oogonial biometry and phylogenetic analyses of the Pythium vexans species group from woody agricultural hosts in South Africa reveal distinct groups within this taxon
- 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 N. Western Avenue, Wenatchee, WA 98801, USAWilhelm J Botha - ARC PPRI, Private Bag X134, Queenswood, Pretoria 0121, South AfricaMarieta Van Der Rijst - ARC Biometry Unit, Private Bag X5013, Stellenbosch 7599, 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(2), pp.157-168
- Academic Unit
- Plant Pathology, Department of
- Publisher
- Elsevier Ltd
- Identifiers
- 99900547466001842
- Language
- English
- Resource Type
- Journal article