The present invention relates to the use of 4-phenylbutyric acid, or one of the salts thereof, for improving the resistance of plants to harmful biological organisms, in particular to bacteria, viruses and nematodes, and for inhibiting hypersensitive cell death induced by such harmful biological organisms. The present invention also relates to the use of 4-phenylbutyric acid, or one of the salts thereof, as an antimicrobial agent for preventing or treating plant diseases caused by phytopathogens.
