Light-induced resistance of broad bean against Botrytis cinerea

This study was designed to investigate the light-induced resistance of broad bean (Vicia faba) against Botrytis cinerea. Yellow (590 nm max) and red (650 nm max) light significantly inhibited the formation of infection hypha from appressoria of B. cinerea on both detached and attached broad bean leaflets. Pretreatment of leaflets with yellow or red light for 24 h before inoculation, also inhibited the formation of infection hypha from appressoria. This indicates that the failure in appressorial penetration of B. cinerea under yellow or red light was not due to the effect of these wavelengths (575 nm to 700 nm) of light on fungal infection behaviour, but due to light-induced resistance in the broad bean against 13. cinerea. Spore germination of B. cinerea, in supernatants of spore suspension droplets of B. cinerea recovered from inoculated broad bean leaflets kept under red light for 48 h after inoculation, was significantly inhibited to a germination rate of 8.2%. However, under darkness the spore germination in infection droplets was not inhibited, with a germination rate of 92.3%. On the other hand, such antifungal activity was also observed in water droplets without spores of B. cinerea on broad bean leaflets kept under red light for 48 h. However, suppressive activity was lower than in infection droplets. These results indicate that irradiation of broad bean leaflets with red light activated production of antifungal substance(s) in the leaf tissues which seem to be responsible for the induced resistance of broad bean against B. cinerea. Further, it was demonstrated that the accumulation of antifungal substance(s) in leaf tissues was increased by infection of B. cinerea.