Host specialization is ancestral in Torymus (Hymenoptera, Chalcidoidea) cynipid gall parasitoids

We detected nucleotide polymorphisms within the genus Gremmeniella in DNA sequences of β-tubulin, glyceraldehyde phosphate dehydrogenase, and mitochondrial small subunit rRNA (mtSSU rRNA) genes. A group-I intron was present in strains originating from fir (Abies spp.) in the mtSSU rRNA locus. This intron in the mtSSU rRNA locus of strains isolated from Abies sachalinensis (Fridr. Schmidt) M.T. Mast in Asia was also found in strains isolated from Abies balsamea (L.) Mill. in North America. Phylogenetic analyses yielded trees that grouped strains by host of origin with strong branch support. Asian strains of Gremmeniella abietina (Lagerberg) Morelet var. abietina isolated from fir (A. sachalinensis) were more closely related to G. abietina var. balsamea from North America, which is found on spruce (Picea spp.) and balsam fir, and European and North American races of G. abietina var. abietina from pines (Pinus spp.) were distantly related. Likewise, North American isolates of Gremmeniella laricina (Ettinger) O. Petrini, L.E. Petrini, G. Laflamme, & G.B. Ouellette, a pathogen of larch, was more closely related to G. laricina from Europe than to G. abietina var. abietina from North America. These data suggest that host specialization might have been the leading evolutionary force shaping Gremmeniella spp., with geographic separation acting as a secondary factor.Key words: Gremmeniella, geographic separation, host specialization, mitochondrial rRNA, nuclear genes.

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A High-Quality Grapevine Downy Mildew Genome Assembly Reveals Rapidly Evolving and Lineage-Specific Putative Host Adaptation Genes

Genome Biology and Evolution ◽

10.1093/gbe/evz048 ◽

2019 ◽

Vol 11 (3) ◽

pp. 954-969 ◽

Cited By ~ 12

Author(s):

Yann Dussert ◽

Isabelle D Mazet ◽

Carole Couture ◽

Jérôme Gouzy ◽

Marie-Christine Piron ◽

...

Keyword(s):

Downy Mildew ◽

Genome Assembly ◽

Population Genomics ◽

Plasmopara Viticola ◽

Plant Diseases ◽

Host Specialization ◽

Grapevine Downy Mildew ◽

Downy Mildews ◽

Genes Encoding ◽

High Level

Abstract Downy mildews are obligate biotrophic oomycete pathogens that cause devastating plant diseases on economically important crops. Plasmopara viticola is the causal agent of grapevine downy mildew, a major disease in vineyards worldwide. We sequenced the genome of Pl. viticola with PacBio long reads and obtained a new 92.94 Mb assembly with high contiguity (359 scaffolds for a N50 of 706.5 kb) due to a better resolution of repeat regions. This assembly presented a high level of gene completeness, recovering 1,592 genes encoding secreted proteins involved in plant–pathogen interactions. Plasmopara viticola had a two-speed genome architecture, with secreted protein-encoding genes preferentially located in gene-sparse, repeat-rich regions and evolving rapidly, as indicated by pairwise dN/dS values. We also used short reads to assemble the genome of Plasmopara muralis, a closely related species infecting grape ivy (Parthenocissus tricuspidata). The lineage-specific proteins identified by comparative genomics analysis included a large proportion of RxLR cytoplasmic effectors and, more generally, genes with high dN/dS values. We identified 270 candidate genes under positive selection, including several genes encoding transporters and components of the RNA machinery potentially involved in host specialization. Finally, the Pl. viticola genome assembly generated here will allow the development of robust population genomics approaches for investigating the mechanisms involved in adaptation to biotic and abiotic selective pressures in this species.

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The Role of Gram-Positive Surface Proteins in Bacterial Niche- and Host-Specialization

Frontiers in Microbiology ◽

10.3389/fmicb.2020.594737 ◽

2020 ◽

Vol 11 ◽

Author(s):

Amy C. Pickering ◽

J. Ross Fitzgerald

Keyword(s):

Surface Proteins ◽

Host Specialization ◽

Gram Positive

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Genetic Diversity and Pathogenic Variability Among Isolates of Colletotrichum Species from Strawberry

Phytopathology ◽

10.1094/phyto.2003.93.2.219 ◽

2003 ◽

Vol 93 (2) ◽

pp. 219-228 ◽

Cited By ~ 51

Author(s):

Béatrice Denoyes-Rothan ◽

Guy Guérin ◽

Christophe Délye ◽

Barbara Smith ◽

Dror Minz ◽

...

Keyword(s):

Sequence Analysis ◽

Sequence Data ◽

Random Amplified Polymorphic Dna ◽

Molecular Data ◽

Its2 Sequence ◽

Host Specialization ◽

Pathogenicity Tests ◽

Colletotrichum Spp ◽

Rapd Polymorphism ◽

Pathogenic Variability

Ninety-five isolates of Colletotrichum including 81 isolates of C. acutatum (62 from strawberry) and 14 isolates of C. gloeosporioides (13 from strawberry) were characterized by various molecular methods and pathogenicity tests. Results based on random amplified polymorphic DNA (RAPD) polymorphism and internal transcribed spacer (ITS) 2 sequence data provided clear genetic evidence of two subgroups in C. acutatum. The first subgroup, characterized as CA-clonal, included only isolates from strawberry and exhibited identical RAPD patterns and nearly identical ITS2 sequence analysis. A larger genetic group, CA-variable, included isolates from various hosts and exhibited variable RAPD patterns and divergent ITS2 sequence analysis. Within the C. acutatum population isolated from strawberry, the CA-clonal group is prevalent in Europe (54 isolates of 62). A subset of European C. acutatum isolates isolated from strawberry and representing the CA-clonal and CA-variable groups was assigned to two pathogenicity groups. No correlation could be drawn between genetic and pathogenicity groups. On the basis of molecular data, it is proposed that the CA-clonal subgroup contains closely related, highly virulent C. acutatum isolates that may have developed host specialization to strawberry. C. gloeosporioides isolates from Europe, which were rarely observed were either slightly or nonpathogenic on strawberry. The absence of correlation between genetic polymorphism and geographical origin in Colletotrichum spp. suggests a worldwide dissemination of isolates, probably through international plant exchanges.

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Host range and physiologic specialization in Rhynchosporium secalis

Australian Journal of Agricultural Research ◽

10.1071/ar9740021 ◽

1974 ◽

Vol 25 (1) ◽

pp. 21 ◽

Cited By ~ 20

Author(s):

SM Ali ◽

WJR Boyd

Keyword(s):

Genetic Diversity ◽

Host Range ◽

Environmental Conditions ◽

Host Specialization ◽

Rhynchosporium Secalis ◽

Host Reaction ◽

Genetic Studies ◽

Barley Cultivars ◽

Adequate Sampling ◽

Pathogenic Variability

The pathogenic variability of isolates of R. secalis collected in Western Australia has been examined on different host genera of the Gramineae and on selected barley cultivars. Depending on the host-isolate combination and the conditions of the test, evidence has been obtained of inter- and intra-isolate variability in both host reaction and isolate pathogenicity. This complicates definitive interpretation of the results, militates against identification of conventional 'races' of the pathogen and shows that R. secalis does not exhibit strict host specialization. Hosts which consistently express resistance or susceptibility under different environmental conditions, and isolates which express their pathogenic characteristics consistently, have been identified. The need for more precise genetic studies and adequate sampling of genetic diversity is emphasized.

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