Race-specific and ulvan-induced defense responses in bean (Phaseolus vulgaris) against Colletotrichum lindemuthianum

The present work aimed to monitor and compare race-specific and ulvan-induced defense responses to race 73 of Colletotrichum lindemuthianum (Cl) in resistant and susceptible bean plants. Under greenhouse conditions, foliar spraying of ulvan, a water-soluble algal polysaccharide, reduced anthracnose severity locally and systemically in susceptible plants by 60 and 40% respectively. Neither race-specific resistance nor ulvan treatment affected both conidial germination and appressorial formation of Cl on leaves. Race 73-specific resistance was associated with a rapid recognition of the pathogen, expressed by a more frequent hypersensitive response in bean epidermal cells. Ulvan increased peroxidase activity in resistant, but not in susceptible plants, and glucanase activity in both resistant and susceptible plants inoculated or not with Cl. This is the first report of an increase in activity of plant defense-related enzymes by treatment of a polysaccharide before pathogen infection.

► Defense responses related to race-specific and ulvan-induced resistances.
► Race-specific resistance to Colletotrichum lindemuthianum was associated with HR.
► Ulvan spraying increased the activity of peroxidase and glucanase in bean plants.
► Neither race-specific resistance nor ulvan affected initial infection processes.
► Ulvan protected bean plants against anthracnose without affecting HR.