The PGPR Serratia plymuthica 4Rx13 produces volatile metabolites that function like antibiotics and inhibit the growth of the phytopathogenic fungi (in-vitro). In presence of bacterial volatiles anti-oxidant enzymes were activated indicating the presence of reactive oxygen species (ROS) in fungal cells. Non-enzymatic lipid peroxidation suggested the disruption of fungal membrane integrity. The fungus Sclerotinia sclerotiorum produced one typical volatile called labda-8 (20),12,14-triene. The ammonia emitted by S. plymuthica 4Rx13 could inhibit fungal growth and evoke oxidative stress in fungi.