Ribosomal gene spacers in Pythium, evolution of species boundaries

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Balcerzak, Malgorzata
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Traditional taxonomy in Pythium is based primarily on growth characteristics and morpholugy and has always been difficult. Rapid, simple and reliable identification of Pythium species mat be possible using molecular techniques. The major objective of this study was to use ribosomal DNA spacer variation to develop molecular markers for identification and classification of Pythium species. The spacer region between the 5S rRNA genes diverges rapidly after speciation and was used as a species-specific hybridization probe for identification of twelve Pythium species. Development of probes was based on the amplification of the intergenic spacer (IGS) between tendemly repeated 5S rRNA genes with primers complementary to the conserved ends of the genes. Probing of gnomic DNA with the 5S spacer probe was useful not only for identification of Pythium isolates to the species level but also allowed for detection of close relationships between species. The interspecific restriction site variation in the intergenic region between the large and the small rDNA gene subunit of 42 isolates representing 5S spacer homology group was also investigated. (Abstract shortened by UMI.)