Analysis Of Genetic Diversity Of Host-associated Populations In B-biotype Bemisia Tabaci By SSR Markers

Bemisia tabaci (Gennadius) first draw major attention in the mid-1980s when severe crop losses were observed in Israel and the southern USA, now it has become an important invasive species that has caused severe damage in many regions of the world. B.tabaci is considered as a complex species comprising a large number of biotypes, among which the B biotype is a particularly aggressive one. The B-biotype spread fast in China since mid-1990 and was listed one of most invasive creatures by quarantine authority. B.tabaci destroys crops by feeding host plants directly, also contains the known whitefly vector of plant-infecting begomoviruses, which were the causal agents of mosaic diseases of many vegetables and flowers. The main purpose of my paper is focusing on the host-associated genetic variation in B-bioype B.tabaci populations and ascertaining the role of host in shaping the genetic structure of B tabaci. In this study, B.tabaci was transferred from the primary host plant (garbage) to other four secondary or native host plants, poinsettia, tomato, cucumber and cotton. In 2005 and in 2006, samples were separately collected from different host plants and microsatellite markers were used to investigate the relationship between host plants and the B-biotype B.tabaci. The overall differentiation among the five hosts was estimated by Fst value during the two years. The genetic structure was assessed at the level of subpopulations (here, one population at two intervals was regarded as two separated subpopulations for comparisons), between hosts, and pariwise comparisions with host-associated populations, using Wright F-statistics, and the main results are as follows:(1)Six polymorphic loci were screened for microsatellite marke. A total of 28 alleles were detected across the 6 loci with the number of alleles per locus ranging from 2 to 9(average＝4.67).(2) Pairwise comparisons of Fst suggested different levels in genetic differentiation between primary host-associated populations and secondary host-associated populations. B.tabaci populations associated with tomatoes showed lower genetic differentiation (Fst＜0) than those on other three secondary hosts in 2005. However, populations on poinsettia, cucumber, cotton and garbage presented a growing genetic differentiation from 2005 to 2006. Only populations in relation with cotton showed a descending on genetic differentiation from 2005 to 2006. We can make sure that the real differentiation time between four alternative host-associated populations and primary population was after 2005.(3) Pairwise comparison of genetic parameters between 2005 and 2006 in all populations suggested Heterozygosity, PIC and Fst value were higher in 2006 than that in 2005. From UMPGA dendrograms, populations on garbage and cucumber were always clustered together. It suggested that they were similar in genetic structure. However, the relationships among other populations were not clear.(4) It showed a remarkably genetic differentiation within populations. Genetic differentiation within populations associated with tomato was highest than that among populations (Fst＝0.3810), also was pronounced in populations on garbage. And the populations related to cucumber was in lowest differentiation in all populations...