Comparative studies on the DNA of Pythium species and some possibly related taxa.

DNA from 14 Pythium species, Verrucalvus flavofaciens and Zoophagus insidians was characterized by CsCl-bisbenzimide density gradients in order to investigate its taxonomic potential. A few incomplete analyses were made for other species. All clearly assignable Pythium species produced three DNA bands in the gradient. Pythium undulatum along with Verrucalvus and Zoophagus produced only two bands. Another possible exception, which needs further investigation, is P. vexans. The DNA had a relatively constant banding pattern in CsCl gradients. The small number (eight) of DNA criteria that were available were subjected to cluster analysis to assess the relationships between replicates and species. This restricted database, similar in size to the number of criteria used in morphological taxonomy, provided an independent assessment of the values that have been attached to generic and subgeneric classifications. This approach enabled assessments to be made of relationships between species that have incomplete life-histories and which therefore lack features essential for traditional taxonomic decisions.