Association of entomopathogenic fungi with non-grafted grapevine Vitis vinifera does not impact plant growth and increases expression of phylloxera responsive defense genes

Grape phylloxera is a sap-sucking insect that poses a major threat to vineyards worldwide by damaging the roots of Vitis vinifera and compromising grape production. Addressing this challenge requires sustainable alternatives to chemical control, and entomopathogenic fungi offer a promising biological approach. In this study, quantitative polymerase chain reaction was used to quantify the expression levels of seven grape phylloxera defense-responsive genes in leaves of Cabernet Sauvignon at 24 h and 120 h after root inoculation with two strains of the entomopathogenic fungus Metarhizium robertsii (one from France (EF3.5(2)) and one from Germany (EF047)). 24 h post-treatment with each strain, six genes (VvPr1, VvPr4, VvPr3.2, VvChib, VvG1, VvPr 1-Like) were up-regulated. Also, 120 h after inoculation with the strain EF047, VvChib and VvG1 were down-regulated. Furthermore, the ability of these two fungal strains as well as two other M . robertsii strains to colonize the rhizosphere and root-endosphere of non-grafted grapevine was evaluated. Grapevines were inoculated via the “ watering” method, and colonization was assessed at 26–28, 47–49, and 68–70 days post-inoculation using a culture based-method. Vegetative growth parameters and leaf pigment parameters were measured throughout the bioassay. All strains persisted in the rhizosphere (60–100% colonization) and to a lesser extent in the root-endosphere (4.8–33.3%) up to 70 days post-inoculation. No adverse effects of fungal colonization on assessed parameters were observed during the bioassay. These results suggest that M. robertsii strains can durably colonize grapevine rhizosphere and root endosphere without detrimental effects and activate early defense responses against root grape phylloxera. The findings highlight the potential of M. robertsii rhizospheric association as a component of integrated pest management strategies in viticulture. • Strains of the entomopathogenic fungus Metarhizium robertsii from different countries and continents can colonize the rhizosphere of grapevine cultivar Cabernet Sauvignon • Association with grapevine roots is stable up to 70 days post-inoculation • Six phylloxera-responsive genes are significantly induced upon inoculation of Metarhizium robertsii