@ARTICLE{TreeBASE2Ref15516, author = {C. D. Garz?n and David M. Geiser and G. W. Moorman}, title = {Amplified Fragment Length Polymorphism Analysis and Internal Transcribed Spacer and coxII Sequences Reveal a Species Boundary Within Pythium irregulare}, year = {2005}, keywords = {}, doi = {}, url = {}, pmid = {}, journal = {Phytopathology}, volume = {95}, number = {}, pages = {}, abstract = {Pythium irregulare is a plant-pathogenic oomycete that causes significant damage to a variety of crops, including ornamentals and vegetables. Morphological as well as molecular studies have reported great genetic diversity within P. irregulare which has raised the question as to whether it is a single species or is actually a complex of morphologically similar (cryptic) species. In this study we used AFLP fingerprinting and DNA sequence analysis of the internal transcribed spacers region of the ribosomal genes (ITS region) and the cytochrome oxidase I and II gene cluster (cox I-II) to characterize 68 P. irregulare isolates from the U.S.. The ITS sequence of a P. irregulare Buisman neotype at the CBS collection (CBSnr 733.94; AY598702) as well as DNA sequences of P. irregulare, P. spinosum and P. sylvaticum from previous studies were included in our analysis. Cluster analysis identified a nineteen-isolate group (IR-II) that separated itself from the rest of the sample (IR-I). Population structure and sequence analyses supported the distinction of IR-I and IR-II and identified IR-II as P. irregulare sensu stricto. IR-I was designated P. irregulare complex (P. i. complex). Two insertion/deletion mutations and nine nucleotide substitutions in the ITS region and three in the cox I and II gene cluster separated the two species. Additionally, they significantly (P>0.01) differed in the frequency of 77% of the alleles analyzed. Gene flow results suggested that P. irregulare sensu stricto and P. i. complex are cryptic species capable of exchanging favorable alleles (Nm=0.72).} }

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