Abstract
Grape Phylloxera, Daktulosphaira vitifoliae, is a gall-forming insect that feeds on the leaves and roots of many Vitis species. The roots of the cultivated V. vinifera cultivars and hybrids are highly susceptible to grape phylloxera feeding damage. The native range of this insect covers most of North America, and it is particularly abundant in the eastern and central United States. Phylloxera was introduced from North America to almost all grape-growing regions across five of the temperate zone continents. It devastated vineyards in each of these regions causing large-scale disruptions to grape growers, wine makers and national economies. In order to understand the population diversity of grape phylloxera in its native range, more than 500 samples from 19 States and 34 samples from the introduced range (northern California, Europe and South America) were genotyped with 32 simple sequence repeat markers. STRUCTURE, a model based clustering method identified five populations within these samples. The five populations were confirmed by a neighbor-joining tree and principal coordinate analysis (PCoA). These populations were distinguished by their Vitis species hosts and their geographic locations. Samples collected from California, Europe and South America traced back to phylloxera sampled in the northeastern United States on V. riparia, with some influence from phylloxera collected along the Atlantic Coast and Central Plains on V. vulpina. Reproductive statistics conclusively confirmed that sexual reproduction is common in the native range and is combined with cyclical parthenogenesis. Native grape phylloxera populations were identified to be under Hardy-Weinberg equilibrium. The identification of admixed samples between many of these populations indicates that shared environments facilitate sexual reproduction between different host associated populations to create new genotypes of phylloxera. This study also found that assortative mating might occur across the sympatric range of the V. vulpina west and V. cinerea populations.
Highlights
Grape phylloxera, Daktulosphaira vitifoliae (Fitch) is an aphid-like root and leaf-feeding insect that is found in most of the world’s vineyards
Samples collected from Arizona, New Mexico, South Dakota and Utah had more triploid data points compared to samples from other regions
Four hundred thirty eight samples were identified as unique multi-locus genotype (MLG); 58 other samples accounted for 25 MLGs where multiple sampling was carried out on the same plant; four samples that were collected from different sites and separated by large distances accounted for 2 unique MLGs (California and Peru samples matched including a triploid allele at the Phy_III_19 marker and samples collected from Indiana and Texas matched); lastly two samples collected from South Dakota from the same site but different plants constituted 1 MLG (Table 1)
Summary
Daktulosphaira vitifoliae (Fitch) is an aphid-like root and leaf-feeding insect that is found in most of the world’s vineyards. Phylloxera gained the reputation as the most important viticultural insect pest after they were accidentally introduced from their native home in North America into France during the mid 1800s [1, 2]. There they found a highly susceptible host, the European grape, Vitis vinifera. Feeding on the young root tips causes hooked galls (nodosities) and feeding on mature structural roots causes large swollen galls (tuberosities), which eventually deform and crack. Years of research determined that grafting the susceptible V. vinifera cultivars onto rootstocks derived from resistant North American Vitis species, which allow feeding on young root tips and leaves, but prevent destructive feeding on the structural roots, was the only effective means of control
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