A new species, Pythium echinogynum, causing severe damping-off of tomato seedlings, isolated from Tunisia, France, and India: morphology, pathology, and biological control

Abstract

Pythium echinogynum, sp. nov. was isolated from soil samples taken from the vineyards of Tunisia, France and also from a lawn sown with turf grass in India. The oomycete is characterised by the presence of both ornamented and smooth walled oogonia. The ornamented oogonia are provided with blunt spines that can be at times curved, 1–2 monoclinous antheridia that can at times wrap around the oogonia, and mostly aplerotic oospores. The oomycete also produces elongated oogonia measuring up to 65 μm long and 24 μm in breadth. The internal transcribed spacer (ITS) region of the rRNA of this new species is comprised of 975 bp and closely resembles (95.9 %) that o P. spiculum and forms a clade together with members of the ornamented or spiny oogonia like P. mammilatum, P. spinosum and P. irregulare but also with those producing smooth-walled oogonia like P. paroecandrum, P. sylvaticum and P. cylindrosporum. However, it has its own characteristics, which are quite distinct from all other species of this genus described so far. In pathogenicty tests, the oomycete was found to be a severe “damping off pathogen” to tomato and cucumber seedlings. However these symptoms were not produced when the new species was grown together with P. lycopersicum—a newly described mycoparasite. The taxonomic description of this new species, its comparison with related oomycetes, the sequence of the ITS region of its rRNA gene, phylogenetic tree with related species and some account of its pathology to tomato and cucumber seedlings are discussed in this article.