The salicylic acid‐dependent defence pathway is effective against different pathogens in tomato and tobacco

The role of salicylic acid (SA) was investigated in basal defence and induced resistance to powdery mildew (Oidium neolycopersici) and grey mould (Botrytis cinerea) in tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum). A comparison of NahG transgenic tomato and tobacco (unable to accumulate SA) to their respective wild types revealed that in tomato, SA was not involved in basal defence against O. neolycopersici but NahG tobacco showed an enhanced susceptibility to O. neolycopersici infection, the effect becoming more obvious as the plants grew older. In contrast, SA played no role in the basal defence of tobacco against B. cinerea, but seemed to contribute to basal defence of tomato against B. cinerea. Activation of the SA‐dependent defence pathway via benzothiadiazole (BTH) resulted in induced resistance against O. neolycopersici in tobacco but not in tomato. Microscopic analysis revealed that BTH treatment could prevent penetration of the Oidium germ tube through tobacco leaves, whereas penetration was successful on tomato leaves irrespective of BTH treatment. In contrast, soil or leaf treatment with BTH induced resistance against B. cinerea in tomato but not in tobacco. It is concluded that the SA‐dependent defence pathway is effective against different pathogens in tomato and tobacco.