The phylloxera of the vine, a cousin insect of the aphids, devastated the French vineyards in the 19th century after an accidental introduction. The serious risk it represents is now under control thanks to tolerant rootstocks, but the insect is still present and poorly understood. INRAE ​​researchers coordinated an international consortium for the sequencing and annotation of the phylloxera genome. The results were published on July 23, 2020 in BMC Biology. They reveal that the origin of the invasion is in North America, possibly along the upper Mississippi. Genomic analyzes also demonstrate the existence of the largest gene family ever identified in a genome to date, possibly involved in the interaction between the insect and its host plant. This new knowledge opens scientific perspectives to improve viticulture, and more broadly on the risks associated with the introduction of exotic species in a territory.

The scientific consortium on the phylloxera genome (Daktulosphaira vitifoliae) was created in 2011 with the aim of shedding new light on the invasion that caused the phylloxera crisis in Europe in the 19th century and better understand the adaptation potential of this insect through the description of its genome. The INRAE-led consortium brought together more than 70 scientists in eight countries, including several CNRS research units in France. At INRAE, additional skills have been mobilized to coordinate this work, specialists in vine diseases, insect genomics and bioinformatics. The researchers also benefited from the technical support of the INRAE ​​BIPAA platform (Bioinformatics Platform for Arthropods of Agroecosystems) to access genomic resources in insects associated with agroecosystems and carry out numerous analyzes.

The researchers organized sampling campaigns for the insect in Europe and the United States and carried out genomic analyzes on individuals. The results provide information about the 19th century invasion. They confirm the identification of Vitis riparia, an American wild vine, as the source of the phylloxera that invaded Europe. More specifically, wild populations located along the Mississippi River are believed to be behind the introduction of phylloxera into French vineyards. Finally, the invasion in the rest of the world would have been made by the populations introduced to Europe. The phylloxera crisis led to the destruction of half of the French vineyard, long changing the economy and geography of viticulture. Ultimately, the use of hardy American vines as rootstocks will save viticulture and enable the rebirth of European vineyards.

Genomic analyzes have revealed the existence of a new gene family, the largest ever identified in a genome. It brings together almost 2,700 genes (the large known gene families rarely exceed 200 genes), accounting for more than 10% of the entire phylloxera genome. These genes would be essential for phylloxera interactions with the vine. They encode small secreted proteins, called "effectors," that are involved in the inactivation of the plant's basic defenses. In its region of origin, the coevolution between plant and insect would have allowed the plant to counteract these attacks, while in Europe cultivated vines did not have adequate defense systems to counter this new pest and its cocktail of effectors.

The results obtained open many perspectives, such as the evolution of insects and, in particular, aphids or genetics and the selection of rootstocks tolerant to phylloxera, two topics that are being worked on at INRAE. They also help to improve knowledge of biological invasions and their potentially disastrous consequences for agriculture and, therefore, for human society and the economy.