| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 93 === An unknown Aphelenchoides sp. was isolated from aquatic plants in a nursery in Taichung, Taiwan. Nematodes were observed to accumulate in the buds of Ceratophyllum demersum, Cabomba spp., and also in the axillar part of Hydrilla verticillata. This Aphelenchoides population had a body length ranging from 0.69-0.97 mm, with slender body shape tapering to a multi-papillate tail tip. The stylet averaged 10 μm with slight basal swelling. The lateral field was approximately 0.18 times body width with four incisures. Females had a single row of oocytes and an well developing postuterine sac extending more than 50% the distance of valve to anus. Males were characterized by the rosethorne-shaped spicules. The morphometrical measurements were very similar to A. fragariae but differed in the number of incisures. Comparing morphometrics and morphology with 40 described Aphelenchoides species found no congruent species. Chemotaxis tests indicated that this nematode could be attracted by the apex and stem tissue sections of Hydrilla verticillata and was later found inside the tissue by staining. Aphelenchoides sp. could be reisolated from Hydrilla verticillata, Lysimachia nummularia , Glossostigma clatinoides, and Hydrotriche sp. after inoculating for 20 days. The plants inoculated with Aphelenchoides sp. showed no disease symptoms nor the phenomenon of endo-parasitic. Among five fungus species tested as the food source, Botrytis cinerae could sustain the largest population of nematodes. The rDNA sequences was obtained for identification and phylogenetic analysis of Aphelenchoides sp. Comparing Aphelenchoides sp. and A. fragariae showed 96% and 95% similarity in ITS1 and ITS2 region respectively, and 100% identical in 5.8S rDNA sequences. The phylogenetic analysis resulted unreliable relationships between Aphelenchoides sp. and other nematodes by using the rDNA sequences. The data suggested Aphelenchoides sp. was potentially an ecto-parasitic nematode according to the observation and the ecological study. Work is underway to describe this population of Aphelenchoides found on aquatic plants in Taiwan as a new species.
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