Exogenous systemin has a contrasting effect on disease resistance in mycorrhizal tomato (Solanum lycopersicum) plants infected with necrotrophic or hemibiotrophic pathogens.

A study was performed to determine the effect of the systemin polypeptide on the bio-protective effect of arbuscular mycorrhizal fungi (AMF) in tomato plants infected with Alternaria solani, Phytophthora infestans or P. parasitica. Before infection, tomato plants were colonized with two different AMF, Glomus fasciculatum or G.