Effects Of Host Plants On The Genetic Differentiation Of B-biotype Bemisia Tabaci Populations

The wordwide B. tabaci is considered as a complex species comprising a large number of biotypes, among which the B biotype is a particularly aggressive one. It's also considered an invasive species of our country. From 1990s, it has been broken out nationwide and caused a economic losses. Presently, it has become an important insect pest on vegetables, flowers, cotton and some other economic crops. A lot of research about the biotypes, biological characteristics, host ranges, damages and control methods of B. tabaci and research on molecular level have been done both here and abroad. In this paper, for the first time we combined the three factors of geographic region, host plant and species characteristic to make a systemic research about the effects of host plants on the genetic differentiation of B-biotype B. tabaci populations using the method of molecular marker.From 2003 to 2004, we collected 35 B. tabaci populations on ten host plants from the nine regions of Beijing, Tianjin, Shandong, Shanxi, Henan, Hebei, Shanghai, Wuhan, Fuzhou and used mt COI molecular markers to identify the biotypes. The results indicated that except for the populations of cucumber, tomato and bean populations collected from Wuhan which didn't obtain the objective fragments, the others are all B biotypes. We landed nine gene sequences to GeneBank and the sequence numbers are DQ017084, DQ017082, DQ011591, DQ011592, DQ011593, DQ011594, DQ017083, DQ011590 andDQ011591.Using AFLP molecular marker to make analysis of the natural populations of Beijing (cabbage, cucumber, tomato, radish, pumpkin), Shanghai (cabbage, tomato, cucumber, eggplant, cushaw, bean), Shandong (tomato, cucumber, eggplant, radish, cushaw, cotton) and the fifth and the tenth generation of the host stress populations (cabbage, cucumber, tomato, poinsettia) separately kept in the greenhouse which had been identified as B biotypes. The results are as follows:First, through the AFLP analysis, similar results were obtained among the natural populations of Beijing, Shanghai and Shandong. The percent of polymorphic allelic loci and heterozygosity of the intraspecific were higher than that of the interspecific. The genetic distance of interspecific and the genetic comparability of intraspecific were low. There was genetic differentiation among the different natural populations, but the level was low, within the populations of the same host plaot there was genetic differentiation to some extent.Second, as for the populations of cucumber and tomato collected from the three different geographic regions, the AFLP analysis indicated that the percent of polymorphic allelic, heterozygosity and genetic distance of the interspecific was lower. There was genetic differentiation among the different populations, but the level was low.Third, there was genetic differentiation between the populations kept on different vegetables and flowers. Compared with the flower population, the heterozygosity of the intraspecific of the vegetables populations was a bit higher.Fourth, the AFLP analysis results of the fifth and the tenth generation of the isolated reared host stress populations were similar with the natural populations. The percent of polymorphic allelic loci and heterozygosity of the intraspecific was still higher than of the interspecific. The genetic distance of interspecific and the genetic comparability of intraspecific were low. There was genetic differentiation among the different natural populations, but the level was low. However, within the populations, there was genetic differentiation to some extent. Compared with the fifth generation, the percent of polymorphic allelic loci and heterozygosity of the interspecific of the tenth generation were a bit higher, and the heterozygosity of the intraspecific was a bit lower.Fifth, compared with the natural populations of Beijing, Shanghai and Shandong, the percent of polymorphic allelic loci, heterozygosity of the interspecific, genetic distance of interspecific and the genetic comparability of intraspecific of the fifth and the tenth generation of the isolated reared host stress populations were bit higher, and the heterozygosity of the intraspecific was a bit lower.