Polydomus karssenii gen. nov. sp. nov. is a dark septate endophyte with a bifunctional lifestyle parasitising eggs of plant parasitic cyst nematodes (Heterodera spp.)

In this study a new taxon was investigated, which was previously isolated from eggs of the cereal cyst nematode<em> Heterodera</em> <em>filipjevi</em>, and roots of the brassicaceous plant species <em>Microthlaspi</em> <em>perfoliatum</em>. The phylogenetic relationships of all nematode and plant isolated strains with different geographic origins were studied using several loci including nuc rDNA ITS1-5.8S-ITS2 (internal transcribed spacer [ITS]), partial 28S nuc rDNA (28S), partial 18S nuc rDNA (18S), partial RNA polymerase II second-largest subunit (<em>rpb2</em>), and partial translation elongation factor 1-α (<em>tef1</em>). <em>Polydomus karssenii</em> gen. nov. sp. nov. (<em>Ascomycota</em>, <em>Pleosporales</em>, <em>Phaeosphaeriaceae</em>) is described and illustrated based on morphological and molecular phylogenetic evidence.