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Geographical Genetic Structure of Xylella fastidiosa from Citrus in São Paulo State, Brazil

A total of 360 Xylella fastidiosa strains were isolated from sweet orange (Citrus sinensis) cv. Pera plants growing in five geographic regions in the Brazilian state of São Paulo. The genetic variation of these strains was determined by 15 variable number tandem repeat (VNTR) and 58 random amplified polymorphic DNA (RAPD) markers. The mean values of genetic diversity (H) of X. fastidiosa strains within each geographic region determined by RAPD (H_RAPD) were substantially lower than H_VNTR values. H_RAPD values ranged from 0.00 to 0.095, whereas the H_VNTR values ranged from 0.024 to 0.285. A highly significant value of Nei's coefficient of gene differentiation (G_ST = 0.355; P = 0.000) was detected among all five populations. Analysis of the molecular variance (AMOVA) also revealed significant genetic differentiation among regions or populations ( φ_STAT = 0.810; P< 0.001). In addition, genetic differentiation among subpopulations (plants) within the regions (φ_STAT = 0.699; P < 0.001) and within each plant (φ_STAT = 368; P < 0.001) were statistically significant. These high values of genetic differentiation among X. fastidiosa strains from different regions suggest a genetic structure according to region of host origin. However, no apparent correlation between genetic distance and region of origin of populations were supported statistically by Mantel analysis (r = 0.27; P = 0.22).