Radopholus similis belong to the plant parasitic nematode family, Pratylenchidae and was recognized that injure the plant. R. similis was generally identified from bananas and plantain in the tropics. However, the occurrence of infection of R. similis on new host plant was confirmed recently. The aim of this study was to report the determination of new host plant for R. similis on Staurogyne sp. The species identification was evaluated the morphological and molecular characteristics of nine R. similis. Molecular assay was designed from the internal transcribed spacer region (ITS) of ribosomal DNA to distinguish species. Nematodes from Staurogyne sp. showed almost similar morphological and morphometric characteristics in general R. similis, but some variation in tail shape was confirmed. Also, male was not detectable. Molecular assay showed a high level (97%) of similarity in the TW81-AB28 and 18S-28S sequences (ITS region) with corresponding NCBI sequence. The quarantine should be more intensely to detect the prohibited nematode.

The aim of the study is to report Radopholus similis detected from Agathis dammara in Thailand as new host plant. Existing host of R. similis was known as coffee, pepper, sugarcane and banana etc. This nematode in this study was observed morphologic character using Carl Zeiss Axioimager M2 and Axiovision Rel. 4.8 program. The result shows that a and b of the female was distorted toward maximum value of original description of species, and b′, c and stylet length was distorted toward minimum value of original description of species. This nematode was morphologically distinguished from originally detected R. similis, but measured value was similar in range of original description of species. For more information, molecular assay was also confirmed the R. similis with 98% homology with the sequence of the internal transcribed spacer region (ITS) of ribosomal DNA. We provided PCR-amplified ITS nucleotide sequence.