title: Re-evaluation of the enigmatic species complex Saprolegnia diclina-Saprolegnia parasitica based on morphological, physiological and molecular data.
abstract: The phylogenetic relationships among isolates of the Saprolegnia diclina-Saprolegnia parasitica complex were investigated based on ITS rDNA sequences, and correlated with morphological and physiological characters. The isolates studied belong to five phylogenetically separate clades. The majority of presumed parasitic isolates, mostly isolated from fish lesions, fell within a clade that comprises isolates which has been variously named as S. diclina Type 1, S. parasitica, Saprolegnia salmonis or just as unnamed Saprolegnia sp. Presence of bundles of long-hooked hairs on secondary cysts, high frequency of retracted germination, and oogonia production at 7 degrees C (when occurring) were characteristic of this clade. A single isolate identified as S. diclina Type 2 clustered in a clade along with Saprolegnia ferax isolates. The isolates identified as S. diclina s. str. (S. diclina Type 3) distributed in two clades and appeared closely related to Saprolegnia multispora and to a number of Chilean isolates identified as Saprolegnia australis. The ITS sequences of clade I were almost identical even though the isolates were of diverse geographical origins and showed physiological and morphological differences and variations in their pathogenicity. This suggest these species reproduces clonally even in apparently sexually competent isolates. Adaptation to parasitism in Saprolegnia might have occurred at spore level by the development of long-hooked hairs to facilitate host attachment and selection of a retracting germination. The use of the name S. parasitica should be assigned to isolates of clade I that contained isolates forming cysts with bundles of long-hooked hairs.
authors: Departamento de Micología, Real Jardín Botánico CSIC, Plaza Murillo 2, 28014 Madrid, Spain. dieguez@ma-rjb.csic.es
authors: Javier
authors: J
authors: Diéguez-Uribeondo
authors: Juan M
authors: JM
authors: Fregeneda-Grandes
authors: Lage
authors: L
authors: Cerenius
authors: Elena
authors: E
authors: Pérez-Iniesta
authors: José Miguel
authors: JM
authors: Aller-Gancedo
authors: M Teresa
authors: MT
authors: Tellería
authors: Kenneth
authors: K
authors: Söderhäll
authors: María P
authors: MP
authors: Martín
mesh_terms: D000349:Africa; D000569:Americas; D000818:Animals; D001208:Asia; D001315:Australia; D002467:Cell Nucleus / Q000235:genetics; D048028:DNA, Algal / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D021903:DNA, Ribosomal Spacer; D005060:Europe; D005393:Fish Diseases / Q000382:microbiology*; D005618:Fresh Water / Q000382:microbiology; D007239:Infections / Q000382:microbiology / Q000662:veterinary*; D010802:Phylogeny; D012487:Salmonidae / Q000382:microbiology*; D044762:Saprolegnia / Q000145:classification* / Q000166:cytology / Q000502:physiology; D013045:Species Specificity; D013170:Spores; D014871:Water Microbiology
chemical_list: D048028:DNA, Algal; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer