Phytopathogenic Mollicutes

Georgia is one of the primary centers of Vitis vinifera domestication and maintains a rich and diverse grapevine germplasm comprising over 500 autochthonous cultivars. Recent investigations have revealed distinct genetic identity and potential tolerance to major grapevine pathogens of this gene pool. Among these, grapevine yellows (GY) diseases, principally “flavescence dorée” and “bois noir” (BN), represent severe threats to viticulture worldwide. Surveys conducted in Georgian vineyards documented for the first time the presence of ‘Candidatus Phytoplasma solani’ (BN-associated phytoplasma) in both grapevines and Convolvulus arvensis, whereas the “flavescence dorée” phytoplasma was not detected. Molecular characterization revealed high genetic diversity among ‘Ca. P. solani’ strains, mainly linked to the bindweed-related pathosystem, and indicated that Georgian grapevine varieties display lower susceptibility to BN compared to international cultivars, which exhibited severe symptoms and yield loss. Subsequent large-scale surveys identified phytoplasmas belonging to the 16SrV group in Georgian vineyards, likely introduced through imported propagation material. Complementary field trials in Piedmont (northwestern Italy), a region heavily infected by “flavescence dorée”, demonstrated that several Georgian cultivars infected by the “flavescence dorée” phytoplasma (genotype M54) exhibited mild or no symptoms and preserved stable berry and wine quality traits, indicating tolerance to the infection. The unique genetic diversity and reduced susceptibility of Georgian V. vinifera varieties to GY make this germplasm a valuable genetic resource for breeding programs aimed at enhancing phytoplasma tolerance while maintaining high oenological quality. The implementation of mandatory certification of grapevine planting materials produced in Georgia (since 2024) and the application of sensitive molecular diagnostic tools will be crucial to prevent phytoplasma spread and ensure the production of healthy nursery stock.