Thiamine induces resistance in tobacco against black shank

Induced resistance by elicitors is considered to be an eco-friendly strategy to stimulate plant defence against pathogen attack. Thiamine (vitamin B1, VB1) can act as a plant defence trigger or priming agent, leading to a rapid counterattack on pathogen invasion, but the underlying molecular mechanisms have not yet been fully elucidated. In the present study, the priming effect of thiamine on tobacco against the disease Phytophthora nicotianae and its biochemical and molecular impact on plant defence mechanisms, as well as the in vitro inhibitory effect of thiamine on P. nicotianae , were evaluated. The results showed that the mycelial growth and sporangium production of P. nicotianae were inhibited by thiamine in a dose-dependent manner. After thiamine pretreatment, the resistance of tobacco plants to P. nicotianae was enhanced, and the severity of tobacco related disease was significantly reduced. In tobacco plants stimulated by thiamine, H 2 O 2 accumulation and catalase (CAT) and peroxidase (POD) and phenylalanine ammonia lyase (PAL) activity levels were enhanced, and seven defence-related genes were upregulated in the plant leaves in order to avoid anthropomorphising plant responses to pathogen attack. Overall, this study demonstrates that thiamine effectively induces resistance against P. nicotianae in tobacco under greenhouse-controlled conditions through a dual mode of action involving direct antifungal activity and induction of host defence mechanisms. It is suggested that thiamine may be an attractive alternative to chemical fungicides in tobacco plant disease management.