For years, chitosan has offered vineyards a natural defense against disease — effective in the laboratory, erratic in the field — and no one could explain the gap between promise and performance. French researchers working across five institutions have now identified the molecular reason: a single receptor protein called VvLYK4-2 acts as the grapevine's primary sensor for chitosan, translating its chemical signal into an immune response. This discovery, published in March 2026, does not resolve every uncertainty, but it gives breeders and scientists a precise biological target — a place to beg