Date Published: January 26, 2017
Publisher: Public Library of Science
Author(s): Karl T. Lund, Summaira Riaz, M. Andrew Walker, Tzen-Yuh Chiang.
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.
Grape phylloxera, Daktulosphaira vitifoliae (Fitch) is an aphid-like root and leaf-feeding insect that is now 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. The leaves of V. vinifera grapes are relatively tolerant to phylloxera feeding, but their fine and structural roots are highly susceptible . 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. Both forms of root damage provide entry to soil-borne fungi and bacteria, resulting in progressively more severe root damage, yield loss and eventual vine death . The introduction of grape phylloxera into Europe resulted in the rapid destruction of vineyards and the collapse of a wine based agricultural economy to such a great extent that it was referred to as the “great French wine blight.” Within 30 years more than 90% of French vineyards were affected by the pest . From France, phylloxera spread across Europe and eventually to grape growing regions around the world. 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.