title: Intraspecific and within-isolate sequence variation in the ITS rRNA gene region of Pythium mercuriale sp. nov. (Pythiaceae).
abstract: Sixteen Pythium isolates from diverse hosts and locations, which showed similarities in their morphology and sequences of the internal transcribed spacer (ITS) region of their rRNA gene, were investigated. As opposed to the generally accepted view, within single isolates ITS sequence variations were consistently found mostly as part of a tract of identical bases (A-T) within ITS1, and of GT or GTTT repeats within the ITS2 sequence. Thirty-one different ITS sequences obtained from 39 cloned ITS products from the 16 isolates showed high sequence and length polymorphisms within and between isolates. However, in a phylogenetic analysis, they formed a cluster distinct from those of other Pythium species. Additional sequencing of two nuclear genes (elongation factor 1 alpha and beta-tubulin) and one mitochondrial gene (nadh1) revealed high levels of heterozygosity as well as polymorphism within and between isolates, with some isolates possessing two or more alleles for each of the nuclear genes. In contrast to the observed variation in the ITS and other gene areas, all isolates were phenotypically similar. Pythium mercuriale sp. nov. (Pythiaceae) is characterized by forming thin-walled chlamydospores, subglobose to obovoid, papillate sporangia proliferating internally and smooth-walled oogonia surrounded by multiple antheridia. Maximum likelihood phylogenetic analyses based on both ITS and beta-tubulin sequence data place P. mercuriale in a clade between Pythium and Phytophthora.
authors.affiliation: Plants and Pathogens Group, Research Institute Earth Nature and Landscape, School of Engineering of Lullier, University of Applied Sciences of Western Switzerland, Jussy, Switzerland.
authors.forename: Lassaad
authors.initials: L
authors.lastname: Belbahri
authors.forename: Adèle
authors.initials: A
authors.lastname: McLeod
authors.forename: Bernard
authors.initials: B
authors.lastname: Paul
authors.forename: Gautier
authors.initials: G
authors.lastname: Calmin
authors.forename: Eduardo
authors.initials: E
authors.lastname: Moralejo
authors.forename: Chris F J
authors.initials: CF
authors.lastname: Spies
authors.forename: Wilhelm J
authors.initials: WJ
authors.lastname: Botha
authors.forename: Antonio
authors.initials: A
authors.lastname: Clemente
authors.forename: Enrique
authors.initials: E
authors.lastname: Descals
authors.forename: Esperanza
authors.initials: E
authors.lastname: Sánchez-Hernández
authors.forename: Francois
authors.initials: F
authors.lastname: Lefort
mesh_terms: D020418:Algal Proteins / Q000235:genetics; D000483:Alleles; D016000:Cluster Analysis; D048028:DNA, Algal / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics*; D020459:Genes, rRNA; D005838:Genotype; D006579:Heterozygote; D008969:Molecular Sequence Data; D020648:Peptide Elongation Factor 1 / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D011110:Polymorphism, Genetic; D011775:Pythium / Q000145:classification* / Q000166:cytology / Q000235:genetics* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D014404:Tubulin / Q000235:genetics
chemical_list: D020418:Algal Proteins; D048028:DNA, Algal; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D020648:Peptide Elongation Factor 1; D014404:Tubulin