The culmination of a decade-long research project has shown potential in solving a nearly 200-year-old insect problem. In the 1860s, the phylloxera aphid arrived in Europe, and quickly decimated all vineyards in France. It took years and innovative approaches to recover from the Great French Wine Blight, as it’s called now. Even today, phylloxera is still around to inflict damage on grape leaves.
Scientists from the University of California, Riverside spent the past 10 years mapping the insect’s genome in an effort to discover how it spreads and how to stop it. The team has identified nearly 3,000 genes that enable phylloxera to colonize and feed on grape vines by creating what researchers describe as “nutritionally enhanced tumors.” The insects live in and feed off of the structures they create, which also protect them from attack by other parasites.
“In effect, phylloxera creates its own refrigerator on the plant that it can feed from whenever it wants," said Paul Nabity, professor of plant-insect ecology at UC Riverside and co-author of the paper.
According to the paper, published in BMC Biology, the structures, known as galls, disrupt the vine's ability to move nutrients and feed itself. They also create wounds in roots that make grapevines more susceptible to fungi and other pathogens, ultimately killing the vines.
Using a combination of genome sequencing, RNA and population resequencing, the research team sought to understand what makes the species spread so effectively and which genes are involved in the attack on grapes.
Phylloxera is native to North America, where it can still cause harm but infinitely less than it does to non-native grapes. The researchers’ population sequencing revealed the pest invasion of 1860 originated in the upper Mississippi River in the United States before spreading to Europe—possibly on steamboats—and then to the rest of the world. While the insect set Europe back on its heels, that was nothing compared to what it did to France—it nearly brought the entire French viticulture to an end. But American and French scientists collaborated on a solution that is still in use today: grafting. During the “Reconstitution,” French and European vines were grafted to the resistant American rootstock. The method was effective then, and continues to be the only effective option nearly 200 years later.
Thus, the genome features the research team, led by Claude Rispe from the French National Institute for Agriculture, Food, and Environment, identified are key to moving past a 200-year-old-grafting method. The final gene catalog contained 25,814 predicted genes and 25,825 transcripts, including more than 2,700 genes with effector attributes, indicating that a large number of genes underlie nutrition, growth, and defense-related processes during interactions with grapevines.
For years, scientists and vintners have tried using statistical genomics to identify heritable regions within breeding stock that may provide resistance to the insect, or do so in limited trials.
However, Nabity says, there was always an unknown as to whether or not these loci in the grape will be resistant to all phylloxera or just the one tested against.
“Knowing all the genes in the insect gives us a map to identify which genes were present and active against the resistance rootstock so we can then measure how common these genes are in other populations of insects,” Nabity explained to Laboratory Equipment. “Thus, knowledge of the insect genes is the only way to know why the plant genes succeed in providing resistance.”
The research opens the door to additional areas of study into the role of effectors in plant feeding and the influence of host plant specialization on genome architecture.
“It will take time but eventually new genotypes will become available that have strong tolerance to most phylloxera and this will significantly reduce any impact of the insect, plus open up new rootstocks that are better adapted to specific soil or climates,” said Nabity. “For people who consume grapes, a phylloxera genome will make more wine and table grape varieties available in some regions. These won’t be GMO, rather plants whose natural traits have been bred into rootstocks used to grow the desired scions. But this will take years to sort out, just not decades as it has in the past.”
Photo: Phylloxera damage to grape leaf. Credit: Paul Nabity/UCR