Characterisation of the two informally designated ITS Clade 6 taxa Phytophthora taxon Forestsoil and P. sp. hungarica

Phytophthora ITS Clade 6 contains numerous informally designated taxa and recently described new species. We report here on the characterisation of the two informally designated taxa P. taxon Forestsoil and P. sp. hungarica. The first culture of P. taxon Forestsoil was collected from soil of an oak‐ Carpinus forest in 1998 and partially characterised later [1]. Subsequently, a few isolates from alder soil with identical ITS sequences to P. t. Forestsoil were reported as P. sp. sylvatica and P. sp. H‐6/02 at Genbank in 2007. At the same time other isolates from alder soil, differing from P. t. Forestsoil and its synonyms in their colony pattern on carrot agar (CA) and at the same 4 positions in their ITS, were named P. sp. hungarica, P. sp. H‐7/02 and P. sp. H‐8/02. Additional ‘hungarica’ isolates were then collected in Alaska [2], also from alder soils or nearby waterways. In our detailed study, the only consistent morphological difference between ‘Forestsoil’ and ‘hungarica’ was still the culture pattern on CA. Both taxa showed similar growth rates and cardinal temperatures, produced similar sporangia, were homothallic with mostly paragynous antheridia and aplerotic oospores often with several ooplasts. Concatenated analyses using 4 nuclear and 2 mitochondrial gene sequences were in concordance with the morphological and physiological features supporting the grouping of ‘Forestsoil’ and ‘hungarica’ isolates into 2 very closely related but distinct clades. These results might help to unravel the taxonomic and phylogenetic position of these informally designated taxa.