Comparative Studies on the DNA of Pythium Species and Some Possibly Related Taxa

Abstract

DNA from 14 Pythium species, Verrucalvus jlavofaciens and Zoophagus insidians was characterized by CsC1-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.

How do obligate parasites evolve? A multi-gene phylogenetic analysis of downy mildews

“…Pythium undulatum and Pythium monospermum were selected as outgroup taxa based on the results of Riethmüller et al (2002). We also considered the somewhat aberrant Pythium vexans (Belkhiri and Dick, 1988;Cooke et al, 2000;Voglmayr, 2003;Lévesque and De Cock, 2004).…”

Phylogenetic studies of Saprolegniomycetidae and related groups based on nuclear large subunit ribosomal DNA sequences

“…Schroeter, and other organisms. Restriction fragment length polymorphisms (RFLPs) of nuclear DNA (e.g., internal transcribed spacer, ITS region) and mitochondrial DNA were used to identify individual species of Phytophthora (Förster et al 1990;Förster and Coffey 1993;Tooley et al 1996), Pythium Pringsheim (Klassen et al 1987;Belkhiri and Dick 1988;Martin and Kistler 1990;Chen and Hoy 1993;Rafin et al 1995) and Saprolegnia Nees (Molina et al 1995). Kageyama (1997) sequenced the ITS region and was able to design species-specific primers for detecting Pythium ultimum Trow from diseased seedlings.…”

Biometry of oogonia and oospores of Saprolegniaceae

“…Baxter (1983) showed that this ratio differed amongst diverse species of Pythium if very young mycelia were used. Belkhiri & Dick (1988) have recorded different yields of DNA (pgDNAg-' wet weight of mycelium) for P. torulosum Coker & Patterson (1.42) and P. diclinum Tokunaga (0.75) which closely correlate with Baxter's observation that the nuclear/protoplasmic volume of P. torulosum is almost twice that for P. diclinum. McNabb et al (1987) and have shown these two species to be very closely related.…”