Studies On Aphelenchida From Pine Wood Infested With Pine Wood Nematode, Bursaphelenchus Xylophilus

Nematodes are the most abundant and diversified group in the animal kingdom and four out of every five metazoan on earth is a nematode. Since Sydney Brenner settled on Caenorhabditis elegans as a model organism to study animal development and behavior in 1965, nematology has made unparalleled advances and become one of the most dynamic and exciting disciplines in the biological sciences. Plant-parasitic nematology owns a brilliant future although it is a young discipline, for the development of nematology is largely attributed to the discovery of the importance of nematodes in agricultural ecosystem and their impact on society. The 21st century might be an era of plant-parasitic nematology with Caenorhabditis elegans as a model system being applied in every aspect of nematology.The pine wood nematode, Bursaphelenchus xylophilus(Steiner & Bubrer 1934)Nickle 1970, is the causal agent of pine wilt disease in East Asia and destroys millions of pine trees every year. However, effective methods of controlling this disease have not yet been developed. Due to the pine wood nematode belongs to the order of Aphelenchida, a nation-wide survey for the presence of Aphelenchida spp. was conducted in China. From which we could learn much about the occurrence of pine wood nematode accompanied by other Aphelenchida species. It might provide some guides for integrated management of the pine wilt disease. Because two new species were discovered during this survey, they were described and illustrated thereafter, and a following hybridization test had been taken to further confirm that they were reproductively isolated. In addition, studies were continued into cytogenetic level to try to understand relationships between nematode species. The main contents are described as follows:1 Investigation on Aphelenchida from pine wood infested with B. xylophilusA nationwide survey for Aphelenchida from pine wood infected with Bursaphelenchus xylophilus (Steiner & Bubrer 1934) Nickle 1970 was conducted in China.Results showed that ten species were found from 300 samples and they belonged to four genera and three families based on morphological identification. From which two new species and two new records from ChinaWhich were Bursaphelenchus xylophilus, B. mucronatus Mamiya & Enda 1979, B. hofmanni Braasch 1998, Aphelenchoides menthae Lisetzkaya 1971, A. macronucleatus Baranovskaya 1963, Seinura tritica Bajaj & Bhatti 1982, S. elmiraensis (van de Linde, 1938) J. B. Goodey, 1960, S. lii Huang & Ye 2006, S. wuae Huang & Ye 2006 and Ektaphelenchidae sp., respectively. Among which S. tritica and S. elmiraensis were new records from China. Besides descriptions, illustrations were provided in the paper. Population variations of these ten species suggested that the pine wood nematode was the dominate species and its occurrence would lead to a significant weakness in diversities of nematodes within pine wood. Results also indicated that biological control potentials of Seinura spp. to pine wood nematode need further studies in China.2 Description of Seinura lii n. sp. and S. wuae n. sp. (Nematoda: Seinuridae)Seinura lii n. sp. and S. wuae n. sp. discovered from dying Pinus massoniana infested with B. xylophilus in Liyang county and Yizheng county, respectively, were described and illustrated in this chaper. S. lii n. sp. is characterised by relatively long female and male bodies (810-1146 and 865-1068μm, respectively), stylet 16-20μm long and lacking knobs, two rows of developing oocytes in the anterior gonad, well-developed postuterine sac (126-182μm long), three lines or incisures in the lateral field, four pairs of subventral papillae on the male tail region, and an elongate-conoid female tail. S. wuae n. sp. is characterised by relatively long female and male bodies (819-1179 and 838-1062μm, respectively), stylet 15-18μm long and with small knobs, three lines or incisures in the lateral field, two or three rows of developing oocytes in the anterior gonad, long postuterine sac (123-172μm long), two pairs of subventral papillae on the male tail region, and an elongate-conoid female tail. Type specimens were deposited in pathology laboratory of Nanjing Forestry University and USDA nematode collection.3 Interbreeding between Seinura lii and S. wuaeDue to Seinura lii was morphologically very similar to S. wuae, a following hybridization test was taken after they were originally described to learn more about the reproductive relationship between them. And the results showed that S. lii and S. wuae were reproductively isolated, additionally biological features of both species might vary considerably. Results also indicated that both Seinura species studied reproduced by amphimixis. It suggested that cytogenetic methods might provide some guides to learn more about the relationships between nematode species which would facilitate nematode taxonomy.4 Cytological features of adult germ-line in two pairs of sibling Aphelenchida speciesStructures of adult germ-line in two pairs of sibling species of Bursaphelenchus xylophilus and B. mucronatus and Seinura lii and S. wuae were characterized. Within and between the two pairs of sibling species, nuclear morphologies of the germ-lines were compared, including germ-cell arrangements and chromosomal behavior. Variance of germ-cell arrangement between species was well correlated with their taxonomic distance. It suggests that studies on cytogenetic features from germ lines might provide valuable information to understand the relationships between nematode species which provide important guides for nematode classification and taxonomy and for better interpreting the evolution of nematode groups and phylogenetic development of nematode populations. In addition, six bivalents of chromosomes were observed in both male and female germ cells in all four species studied. To sum up, a nation-wide survey for the presence of Aphelenchida spp. from pine wood infested with pine wood nematode was first conducted. Descriptions were provided and illustrations were compared in the paper. And an issue that biological control potentials of Seinura spp. to pine wood nematode needed further studies in China was presented. All of which might provide some guides to the management of pine wilt disease. Two new Seinura species and two new records from China were discovered during the survey. The two new species were described and reported in the international journal, Nematology. This is the first time to report new species in the genus Seinura from China, which will initiate studies on morphology and taxonomy of Seinura in China. Besides, paratype specimens were deposited in the well-recognised international nematode collection (USDANC), which might facilitate academic communication with international experts and enhance national prestige to some degree. In addition, a hybridization test was taken and reproductive relationship was discussed, which offered some guides for the later part of research. Finally, studies had been put into cytogenetic level. An idea of"cytogenetic features from germ lines might provide valuable information to understand the relationships between nematode species"was presented which might serve for nematode taxonomy and interpretation of phylogenetic development of nematode populations.