Genetic structure in native populations of grape phylloxera (Homoptera : Phylloxeridae)

Random amplified polymorphic DNA (RAPD) markers were used to study genetic structure and diversity in native grape phylloxera populations growing on V itis arizonica Englemann in central Arizona and on V. riparia Michaux in Ne w York. RAPD data from the Arizona collections were clustered into 3 subpop ulations, whereas data from the New York collections were not clustered, wh ich reflected topographic features and the distribution of the sampled vine s. Similarity coefficients of the 2 collection areas had similar ranges (0. 89-1.0). The similarity coefficient between the Arizona and New York collec tions was 0.62. Analyses of molecular variance were-used to partition the v ariance in genetic distances, and confirmed the results of the dendrogram c lustering. The clustering of the Arizona populations is likely the result o f gene flow restriction caused by geographic isolation. Greater diversity w as expected among the Arizona populations. That diversity levels were simil ar suggests that other factors, such as inbreeding or past population histo ry, must play a role in the relatively low level of diversity found in Ariz ona.