| Summary: | 碩士 === 中興大學 === 植物病理學系所 === 95 === Nine of the 11 nematicide-resistant Rhabditis sp. populations, but only two out of 12 Aphelenchoides besseyi populations, lost their resistance after 16 months in the absence of nematicides. Calculated LC50 of Caenorhabditis elegans with four nematicides, and selected nematicide- resistant populations. The free-living nematodes, Rhabditis sp. and three plant-parasitic nematodes, A. besseyi, Bursaphelenchus sp. and B. xylophilus were treated with low concentrations of the 4 nematicides to induce the resistant nematodes and to treated with high concentration of nematicide to select the nematodes. The LC50 of C. elegans with ethoprop, phenamiphos, carbofuran or oxamyl was 260.8 ppm, 511.6 ppm, 783.7 ppm and 803 ppm respectively. Seventy eight induced or selected nematode populations with different levels of nematicide resistance were obtained. C. elegans and A. besseyi tested were more sensitive to organophosphate nematicides than carbamate nematicides. Our results also showed that free-living nematodes were more resistant to all four nematicides than plant-parasitic nematodes tested. Moreover, B. xylophilus was more resistant to the tested nematicides than Bursaphelenchus sp.
Primer sets of C. elegans were applied to characterization the acetylcholinesterases from nematodes that have different nematicide resistances. Eight populations from ten C. elegans nematicide-resistance populations resulted a 2.0 kb cDNA region C. elegans ace-1 primers. But only one population from ace-2 primers, four populations from ace-3 primers and no population could be amplified by ace-4 primers. The results indicated the expression levels of these 4 genes are not equal. Only CO1000 population has mutations in the ace-1 cDNA sequence.
As to other four nematodes, no cDNA regions were amplified by C. elegans ace-1 and ace-4 primers, but there were various cDNA regions resulted by using ace-2 and ace-3 primers. Four ace-2 cDNA fragment from Rhabditis sp. and A. besseyi were compared to C. elegans ace-2, and only had 24.7~24.1 % similarity. When blasted in the NCBI, the sequences of AC500B-1.1 and AO500B-1.1 had somewhat similarity to C. elegans X chromosome.
Furthermore, a new set of the ace-1 primers was designed from the similar fragments of C. elegans, C. briggsae, M.incognita and M. javanica ace-1 gene to amplify five untreated nematodes. Different cDNA regions from four nematodes; C. elegans, Rhabditis sp., Bursaphelenchus sp. and B. xylophilus except A. besseyi were amplified and five sequences from 2 nematode species were blasted with C. elegans ace-1 and NCBI database. The results showed the 5 sequences had only 23.6~27.6 % similarity to C. elegans ace-1, among them, JCKmA-1.2 and JCKmA-0.6 were somewhat similar to a fragment of Drosophila melanogaster and Chimpanzee（Pan troglodytes） X chromosome.
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