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Pythium recalcitrans sp. nov. revealed by multigene phylogenetic analysis

     Instituto Mediterráneo de Estudios Avanzados, IMEDEA (CSIC-UIB), Miquel Marquès 21, 07190, Esporles, Balearic Islands, Spain

Lassaad Belbahri
Gautier Calmin
François Lefort

     Laboratory of Applied Genetics, School of Engineering of Lullier, University of Applied Sciences of Western Switzerland, 150 route de Presinge, 1254 Jussy, Switzerland

Chris F.J. Spies
Adele McLeod

     University of Stellenbosch, Department of Plant Pathology, Private Bag X1, Matieland 7602, South Africa

A new species of Pythium collected from grapevine roots (Vitis vinifera) in South Africa and roots of common beet (Beta vulgaris) in Majorca, Spain, is described. The phylogenetic position of the new species was investigated by multigene sequence analyses of the internal transcribed spacers (ITS1 and ITS2) of the rDNA region, as well as three other nuclear and three mitochondrial coding genes. Maximum likelihood phylogenetic analyses based on ITS rDNA and concatenated β-tubulin and cytrochrome c oxidase II alignment place Pythium recalcitrans together with P. sylvaticum and P. intermedium. Pythium recalcitrans sp. nov. is morphologically almost indistinguishable from other Pythium species that only form hyphal swellings in culture. However its species status is justified by the distinctiveness of the DNA sequences in all the genes examined. In culture P. recalcitrans exhibits fast radial growth, abundant spherical to subglobose hyphal swellings but produces no zoosporangia. Sexual structures are not seen in agar media but form in autoclaved grass blades floated on water. Multiple antheridia (1–7) are encountered with most of them diclinous and crook-necked. Oospores are thin-walled and either aplerotic or plerotic. P. recalcitrans was pathogenic to seedlings of Beta vulgaris and Solanum lycopersicum.

Key words: actin, -tubulin, β-tubulin, cox I and II, ITS rDNA, nadh I, oomycetes, plant pathogen, Pythium phylogeny

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