Submitted to: BioMed Central (BMC) Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/23/2013
Publication Date: 1/15/2014
Citation: Islam, M., Roush, T., Walker, M., Granett, J., Lin, H. 2014. Reproductive mode and fine-scale population genetic structure of grape phylloxera (Daktulosphaira vitifoliae) in a viticultural area in California. BioMed Central (BMC) Genetics. 14:123. Interpretive Summary: Grape phylloxera (Daktulosphaira vitifoliae) is one of the most devastating insect pests in many grape production regions worldwide. Despite success of phylloxera control by use of resistant rootstocks, information regarding reproductive mode, genetic structure, and diversity of phylloxera in various viticultural environments remains unclear. In this study, DNA-based molecular markers were used to assess genetic diversity and structure of phylloxera populations in four vineyard-sites in California. Since phylloxera populations in California are believed to reproduce asexually, genetic diversity is expected to be limited. Results from this study, however, demonstrated high levels of diversity in four populations. Genetic analysis also suggested occurrence of both asexual and sexual reproduction in California populations. This study clearly separates phylloxera populations into two major groups: one associated only with AXR#1 rootstocks, defined as “biotype B”, and another associated with vinifera-based rootstocks, known as “biotype A”. Results from this study provided new information for better understanding of genetic diversity, host selection, and evolutionary potential of phylloxera populations in California.
Technical Abstract: Grape phylloxera (Daktulosphaira vitifoliae) is regarded as one of the world's most important viticultural pests. However, reproductive mode, genetic structure, and host adaptation of phylloxera in various viticultural environments remain unclear. In this study, reproductive mode and genetic structure of phylloxera were examined by analyzing microsatellite markers of samples from four vineyard-sites with different rootstocks in California. Genetic diversity is expected to be low due to parthenogenetic reproduction of phylloxera in California. However, this study showed high levels of diversity in Napa and Yolo county populations with a large number of unique genotypes-average alleles of 2.1 to 2.9 and observed heterozygosity of 0.330 to 0.388 per population. Reproduction diversity index (G:N—unique genotypes versus number of samples) ranged from 0.500 to 0.656 among populations. Moreover, high variation of F-inbreeding statistics (FIS) was observed among different loci in each vineyard-site. Genetic structure analysis using Unweighted Pair Group Method with Arithmetic Mean (UPGMA) and various measures of population differentiations: F-statistics (FST), Principal Component Analysis (PCA), and gene flow analysis consistently separated a population associated with AXR#1 rootstock from populations associated with other vinifera-based rootstocks. Genetic diversity, G:N ratio, probability of sexual reproduction (Psex) and FIS data suggested occurrence of both parthenogenetic and sexual reproduction in California populations. This study clearly identified two major genetic groups of phylloxera obtained from various rootstocks, with one group exclusively associated with AXR#1, defined as “biotype B”, and another group (biotype A), associated with vinifera-based rootstocks. Genetic structure of AXR#1-associated populations was, therefore, in accordance with distinct strain status, suggesting strong selection on AXR#1-adapted phylloxera populations. Results from this study provide new information for better understanding of genetic diversity, host selection, and evolutionary potential of phylloxera populations in California.