Genetic Diversity of Grape Phylloxera Leaf-Galling Populations on Vitis species in Uruguay

Grape phylloxera (Daktulosphaira vitifoliae) feeds exclusively on Vitis species, preferentially on leaves of American Vitis species and roots of European Vitis vinifera. Over the last 15 years, extensive feeding and galling on V. vinifera leaves have been observed in Italy, Brazil, and Peru. In Uruguay, D. vitifoliae infestations on V. vinifera leaves were detected in very high densities. The cause of this unexpected insect behavior is unknown, but possible explanations include selection pressure for more aggressive native strains in the new context of vigorous plants replacing old vineyards, loss of resistance in plants due to improvement programs, or importation of exotic strains of the insect. The aims of this research were to evaluate genetic diversity of leaf-galling populations of Uruguayan phylloxera, to estimate genetic distances among them, and to compare Uruguayan and foreign phylloxera populations (Brazilian, Peruvian, and European). Genetic distances between root and leaf samples from the same plant were also estimated. Four polymorphic microsatellite primers were used in this study. In the analysis of leaf- and root-insect populations from the same plant, different insect genotypes were found on grafted vines, with one genotype on the rootstock and one on the V. vinifera (cultivar scion). For Uruguayan leaf-galling insect populations, the average number of alleles per locus was 4.25. Genetic variance found among individuals within populations was 88% (SE = 2.298, p < 0.001), and 12% between populations (SE = 0.319, p < 0.001). An F-ST of 0.211 (p < 0.001) suggests limited genetic flow among populations. Significant deviation from Hardy-Weinberg equilibrium detected for the loci analyzed and the negative F-IS values together suggest that parthenogenesis could be the reproductive mode. Genetic diversity found in this work shows considerable potential for host adaptation to environmental variability.