Photodynamic Inactivation as a New Weapon Against Plant Fire Blight Disease: Proof of a New Dawn of Environmentally Friendly Crop Protection.

Fire blight, caused by Erwinia amylovora, severely affects apple and pear orchards on a global scale. Conventional treatment includes the application of antibiotics such as streptomycin during bloom, which promotes resistance. Photodynamic inactivation (PDI) is based on the light-induced and photosensitizer-mediated overproduction of reactive oxygen species for killing microbes. This study develops PDI using the natural photosensitizer sodium magnesium chlorophyllin (Chl) from the laboratory to field application. Laboratory experiments showed commercial-ready SUN-D products (Chl + EDTA) were highly effective against E. amylovora (395 nm LED, total kill at 53.2 J cm(-2)), regardless of streptomycin resistance phenotype. No resistance to Chl developed after 15 treatment cycles. Molecular dynamics simulations suggest that EDTA lowers the energy barrier for chlorin e6, enhancing membrane penetration. Field trials at two locations using sunlight illumination showed that SUN-D controlled blossom blight comparably to antibiotics. Photodynamic inactivation with SUN-D offers a promising, resistance-independent addition to current fire blight management strategies.