Morphological plasticity in the rice root nematode, Hirschmanniella oryzae (van Breda de Haan, 1902) Luc & Goodey, 1964 from Korea, with inferences from its ribosomal and mitochondrial DNA

A population of Hirschmanniella oryzae (van Breda de Haan, 1902) Luc & Goodey, 1964 with extreme morphological and morphometric variations was reported from rhizospheric soils sampled from a paddy rice-garlic double cropped farm in Korea. Females and males are morphologically characterized and their linked DNA sequence data supplied. Morphological and morphometric data revealed extreme intraspecific variation, especially in body length, stylet length, tail length, tail terminus shape and body ratios. But, despite the significant morphological and morphometric divergence, inferences from the analyses of the 18S-rRNA, D2-D3 expansion segment of 28S-rRNA and ITS1–5.8S-ITS2 of rRNA partial sequences confirmed that the studied population belongs to H. oryzae. The current morphometric data extends total ranges recorded for H. oryzae, but also, overlaps all morphometric characters of H. belli Sher, 1968. However, the available molecular DNA markers (18S- and 28S-rRNA) strongly support the validity of the two species. Therefore, H. belli is herein considered a cryptic sibling species of H. oryzae. Morphological divergence is becoming a common phenomenon in Hirschmanniella spp., and there is a continuous need to apply integrative taxonomic identification considering both morphological and molecular markers to supplement the current generic compendia. The COI gene sequences of H. oryzae are herein supplied for the first time.