Taxonomic notes on three Tylenchorhynchus spp. (Nematoda, Telotylenchidae) associated with turfgrass in Korea

Two populations of Tylenchorhynchus annulatus, recovered from loamy-soil rhizosphere of Zoysia japonica from Korea are described and illustrated based on integrative taxonomy, considering both morphological and molecular phylogenetic inferences from analyses of the 28S-rRNA and ITS-rRNA gene sequences. One of the populations manifested variation in species diagnostic characters; continuous lateral field incisures past the phasmid was not a constant character in all specimens examined, with some specimens manifesting fusion of inner incisures of the lateral field below the level of the phasmid and incomplete areolation of the lateral fields. The fusion of the inner incisures of the lateral field past the phasmid level is therefore a variable character within the group, and when used alone, may not be taxonomically reliable to delineate species within the genus. This is molecularly supported by genetic resemblance of the two populations with other characterized T. annulatus isolates based on D2-D3 expansion segment and ITS-rRNA. The overlapping disparities between the two populations are therefore herein treated as intraspecific variations within T. annulatus populations. Furthermore, comparison within all the published sequences of T. annulatus are made and recommendations for sequence corrections are given. Tylenchorhynchus thermophilus is characterized herein for the first time in Korea while T. annulatus and T. claytoni are molecularly confirmed.