Evidence for high degrees of specialisation, evolutionary diversity, and morphological distinctiveness in the genus Bremia

Choi, Young Joon; Thines, Marco; Runge, Fabian; Hong, Seung Beom; Telle, Sabine; Shin, Hyeon Dong

doi:10.1016/j.funbio.2010.10.010

Cited by 32 publications

(23 citation statements)

References 43 publications

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“…However, there is an increasing body of evidence from recent studies combining molecular phylogenetics with morphological investigations, e.g. from Bremia [9], Peronospora [8], [12], [52], [53], and Hyaloperonospora [54], [55] that sporangial dimensions might be a useful character for species delimitation. In our investigation, there was a positive correlation between the length and the width of sporangia, so the tendency for longer sporangia to also be broader is given.…”

Section: Discussionmentioning

confidence: 99%

“…The impact of host matrix on sporangial dimensions and a limited number of additional characteristics has already been shown for P. cubensis [26], [33]. But it is currently unclear, how the broad set of characteristics currently used for species delimitation [8], [9], [12], [34] is influenced by the host matrix, and if increasing phylogenetic distance of the hosts would lead to stronger differences in the morphology of the pathogen, or if other factors are more important. In addition, it is important to assess which characters are most and least influenced by the host matrix to enable the identification of characters by which known species on new hosts could be reliably identified.…”

Section: Introductionmentioning

confidence: 99%

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Which Morphological Characteristics Are Most Influenced by the Host Matrix in Downy Mildews? A Case Study in Pseudoperonospora cubensis

2012

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Before the advent of molecular phylogenetics, species concepts in the downy mildews, an economically important group of obligate biotrophic oomycete pathogens, have mostly been based upon host range and morphology. While molecular phylogenetic studies have confirmed a narrow host range for many downy mildew species, others, like Pseudoperonospora cubensis affect even different genera. Although often morphological differences were found for new, phylogenetically distinct species, uncertainty prevails regarding their host ranges, especially regarding related plants that have been reported as downy mildew hosts, but were not included in the phylogenetic studies. In these cases, the basis for deciding if the divergence in some morphological characters can be deemed sufficient for designation as separate species is uncertain, as observed morphological divergence could be due to different host matrices colonised. The broad host range of P. cubensis (ca. 60 host species) renders this pathogen an ideal model organism for the investigation of morphological variations in relation to the host matrix and to evaluate which characteristics are best indicators for conspecificity or distinctiveness. On the basis of twelve morphological characterisitcs and a set of twelve cucurbits from five different Cucurbitaceae tribes, including the two species, Cyclanthera pedata and Thladiantha dubia, hitherto not reported as hosts of P. cubensis, a significant influence of the host matrix on pathogen morphology was found. Given the high intraspecific variation of some characteristics, also their plasticity has to be taken into account. The implications for morphological species determination and the confidence limits of morphological characteristics are discussed. For species delimitations in Pseudoperonospora it is shown that the ratio of the height of the first ramification to the sporangiophore length, ratio of the longer to the shorter ultimate branchlet, and especially the length and width of sporangia, as well as, with some reservations, their ratio, are the most suitable characteristics for species delimitation.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Which Morphological Characteristics Are Most Influenced by the Host Matrix in Downy Mildews? A Case Study in Pseudoperonospora cubensis

2012

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“…A similar case of evolutionary radiation driven by physiological and ecological similarities of hosts rather than host relationships was documented for the floricolous downy mildews, which constitute a monophyletic lineage of several closely related species parasitizing flowers of various distantly related euasterid hosts (Voglmayr 2003;Thines and Kummer 2013). Therefore, this is another example of the importance of host jumps for speciation in the genus Peronospora (Voglmayr 2003(Voglmayr , 2008Thines et al 2009a, 2011, Thines and Kummer 2013Voglmayr et al 2014b) and downy mildews in general (e.g., Thines et al 2009b;Choi et al 2011b;Runge et al 2011;Thines 2014).…”

Section: Discussionmentioning

confidence: 64%

Peronospora odessana sp. nov., a downy mildew pathogen of a Tertiary relict species, Gymnospermium odessanum

Voglmayr

Korytnianska

2015

Mycol Progress

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A new species of Peronospora is described from Gymnospermium odessanum, a rare spring geophyte considered a Tertiary relict in the northwestern Black Sea region of Ukraine, Moldova and Romania. Phylogenetic analyses based on a combined matrix of the internal transcribed spacer-large subunit (ITS-LSU) ribosomal DNA (rDNA) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) and cox2 genes demonstrate that it is a clearly distinct undescribed species. Morphological descriptions and illustrations of its oospores, conidiophores and conidia are provided. Despite its distinctive disease symptoms, the species has remained undetected until now, probably due to the rarity of its host. Peronospora odessana is the second species from Berberidaceae and is morphologically clearly distinct from P. achlydis on Achlys japonicus. The closest relatives of P. odessana were not revealed, but it is closely related to Peronospora bulbocapni, P. dicentrae and P. chrysosplenii, the hosts of which are also spring geophytes. Sequence data confirm that cox1 and cox2 are good barcoding loci; they show a similar number of nucleotide differences to its closest relatives.

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“…Our results on grapevine downy mildew illustrate how biotrophic plant pathogens can diversify by host plant specialization. They are in agreement with phylogenetic studies that have recently reported the presence of distinct pathogen species on a specific host plant family, including Albugo and Hyaloperonospora on Brassicaceae (Goker et al ., ; Ploch et al ., ), Bremia on Asteraceae (Choi et al ., ), Peronospora on Fabaceae and on Lamiaceae (Garcia‐Blazquez et al ., ; Choi et al ., ; Thines et al ., ) and Peronosclerospora on Poaceae (Telle et al ., ). Nevertheless, the proximal mechanisms responsible for such adaptive radiation in downy mildews remain unknown.…”

Section: Discussionmentioning

confidence: 99%

“…The rapid ecological divergence experienced by plant pathogens implies that many may, in fact, be complexes of sibling species, an idea put forward by Crous & Groenewald (): ‘Show me a plant pathogen, and I will show you a species complex’. Since then, there has been abundant phylogenetic evidence supporting the view that many current names of well‐known plant pathogens actually mask complexes of cryptic species (O'Donnell et al ., ; Steenkamp et al ., ; Fournier et al ., ; Le Gac et al ., ; Garcia‐Blazquez et al ., ; Choi et al ., ). In addition to the divergent selective pressures caused by specialization on the host, plant pathogens have evolved in response to the agro‐ecosystem.…”

Section: Introductionmentioning

confidence: 99%

Phylogenetic and experimental evidence for host‐specialized cryptic species in a biotrophic oomycete

et al. 2012

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Key words: disease emergence, evolution of aggressiveness in agro-ecosystem, host plant specialization, host shift, plant-pathogen interaction, Plasmopara viticola (the causal agent of grapevine downy mildew), quantitative adaptation to cultivar, Vitis vinifera and wild relatives. SummaryAssortative mating resulting from host plant specialization has been proposed to facilitate rapid ecological divergence in biotrophic plant pathogens. Downy mildews, a major group of biotrophic oomycetes, are prime candidates for testing speciation by host plant specialization.Here, we combined a phylogenetic and morphological approach with cross-pathogenicity tests to investigate host plant specialization and host range expansion in grapevine downy mildew. This destructive disease is caused by Plasmopara viticola, an oomycete endemic to North America on wild species and cultivated grapevines.Multiple genealogies and sporangia morphology provide evidence that P. viticola is a complex of four cryptic species, each associated with different host plants. Cross-inoculation experiments showed complete host plant specialization on Parthenocissus quinquefolia and on Vitis riparia, whereas cryptic species found on V. aestivalis, V. labrusca and V. vinifera were revealed to be less specific. We reconstructed the recent host range expansion of P. viticola from wild to cultivated grapevines, and showed that it was accompanied by an increase in aggressiveness of the pathogen.This case study on grapevine downy mildew illustrates how biotrophic plant pathogens can diversify by host plant specialization and emerge in agrosystems by shifting to cultivated hosts. These results might have important implications for viticulture, including breeding for resistance and disease management.

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Evidence for high degrees of specialisation, evolutionary diversity, and morphological distinctiveness in the genus Bremia

Cited by 32 publications

References 43 publications

Which Morphological Characteristics Are Most Influenced by the Host Matrix in Downy Mildews? A Case Study in Pseudoperonospora cubensis

Which Morphological Characteristics Are Most Influenced by the Host Matrix in Downy Mildews? A Case Study in Pseudoperonospora cubensis

Peronospora odessana sp. nov., a downy mildew pathogen of a Tertiary relict species, Gymnospermium odessanum

Phylogenetic and experimental evidence for host‐specialized cryptic species in a biotrophic oomycete

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