2019 Volume 49 Issue 2 Pages 29-33
In 1986, an undescribed Heterodera species found in continuously cultivated soybean fields was reported in Japan. Only dead nematodes of the population are currently available for taxonomic description of this species. In 2016 a new soybean parasitic cyst nematode was described as H. sojae in Korea. These two nematodes showed morphological similarity and thus were expected to be conspecific. In this study, the nucleotide sequences of the nuclear ribosomal RNA gene region were examined to confirm whether the unknown cyst nematode was H. sojae. BLAST results showed that the nucleotide sequences of the large subunit rRNA D2–D3 expansion segments (740 bp) and the internal transcribed spacer (ITS) fragment covering 3’-end of the ITS1, the entire 5.8S rRNA and the partial ITS2 (368 bp) both were by far the most similar to the sequences of H. sojae. Together with morphological similarity including the ambifenestrate vulval cone with a particularly short vulval slit, the unknown cyst nematode was identified as H. sojae. In addition, the duplex PCR assay targeting the ITS2 region to discriminate H. sojae was developed to amplify a 201 bp product specific to H. sojae as well as ca. 450–480 bp products across cyst nematodes. No further detections in Japan since the first report in 1986 and detections limited to a few countries including Korea, China and Japan to date imply H. sojae has occurred for a long time as a minor pest of soybean in East Asia.