Evidence for subdivision of the root-endophyte Phialocephala fortinii into cryptic species and recombination within species.
The genetic structure of the root-endophyte Phialocephala fortinii was analyzed in three study sites using 11 single-copy RFLP probes. A total of 541 strains isolated from surface-sterilized, fine roots (diameter 0.5-3 mm) of Norway spruce (Picea abies) were examined. The average gene diversity (H) was high in all three study sites. Cluster analysis showed that up to four well-separated clusters of multi-locus haplotypes were present within the sites. Significant population subdivision was detected among these clusters, suggesting that groups of multi-locus haplotypes were reproductively isolated and that P. fortinii is a species complex composed of several cryptic species. This hypothesis was supported by ISSR-PCR which showed clusters consistent with those of the multi-locus haplotypes identified by RFLP analysis. In contrast, ITS sequence analysis did not allow to separate the species as clearly. The index of association (IA) did not deviate significantly from zero within any cryptic species, suggesting that recombination occurs within these species. Cryptic species occurred sympatrically. Thalli of two cryptic species were detected in the same 5-mm-long root segment in one instance. No significant differentiation was observed among populations of the same cryptic species in forest stands located approximately 5 km from each other. This finding is consistent with significant gene flow over this spatial scale. In addition, several isolates with both identical multi-locus haplotype and identical ISSR fingerprint were found at each study site indicating genotype flow or a recent common history between study sites.
Swiss Federal Institute of Technology, Department of Environmental Sciences, Forest Pathology and Dendrology, ETH-Zentrum, CH-8092 Zürich.
Christoph R
CR
Grünig
Bruce A
BA
McDonald
Thomas N
TN
Sieber
Scott O
SO
Rogers
Ottmar
O
Holdenrieder
D001203:Ascomycota / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D016000:Cluster Analysis; D016172:DNA Fingerprinting; D004271:DNA, Fungal / Q000032:analysis / Q000302:isolation & purification; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000302:isolation & purification; D005800:Genes, Fungal; D014644:Genetic Variation; D006239:Haplotypes; D010802:Phylogeny; D028222:Picea / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA
D004271:DNA, Fungal; D021903:DNA, Ribosomal Spacer