Studied On Nematodes Of Onion Soil And It's Population Changing In Jiayuguan Gansu

1. Nematode species extracted from onion soil in Jiayuguan cityThe neatodes species were studied in Xinchen town Jiayuguan Gansu province,from March to September in 2008.The results showed: seventeen species which belonged to seventeen genera were extracted from soil samples.Plant parasitic nematodes : Psilenchus hilarulus,Filenchus vulgaris,Helicotylenchus digonicus,Tylenchorhynchus maximus,Aphelenchus avenae.Non-Plant nematodes : Bacterivorous nematodes,Omnivorous and predatory nematodes.Omnivorous and Predatory nematodes: Aporcelaimellus obscurus,Ecumenicus monohystera,Mesodorylaaimus bastiati,Discolaimus texanus,Alaimus primitivus,Geomonhystera villosa.Bacterivorous nematodes: Eucephalobus oxyuroides,Chiloplacus propinquus,Mesorhabditis spp.,Diploseapter spp.,Rhabditoides spp.,Pelodera spp.2. The change rules of nematode population density in onion soil in Jiayuguan cityDensity statistics of the separated nematode were carried out,the result showed that: during the whole growing season of onion, the number of all kinds of nematodes was the least at the period of pre-transplant, and then reached peak at the enlargement period.The densities of non-plant nematode were higher than that of plant nematodes during the whole growing season.The density of plant nematodes was 90 per 100 ml soil, with an incidence of 13.4% of all nematodes in the enlargement period; while the density of non-plant nematodes reached 702 per 100 ml soil with an incidence of 88.6%,7.8 times higher than that of plant nematodes .The plant dominant nematode species in this region was A. avenae. In enlargement period the highest density of this nematode reached to 58 juveniles per 100 ml soil and accounted for 64% of the whole nematodes. The non-plant dominant nematode species in this region was Mesorhabditis spp. In enlargement period the highest density of the nematode reached to 275 per 100 ml soil and accounted for 39% of the whole non-plant nematodes.The result of dominance comparision of soil nematode in the enlargement period showed: bacterivorous nematodes accounted for 82%,while plant parasitic nematodes, omnivorous and predatory nematodes accounted for 11%,7% respectively.3. The relativily analysis of plant nematode population density and onion Basal rot disease According to relativily analysis,there was the distinct positive relativily between the nematode population and the development of the basal rot diseases of onion.