Antifungal activity of extracts from Justicia species against Fusarium graminearum.

Fusarium graminearum causes destructive ear rot diseases in maize and wheat. New antifungals are essential to combat this pathogen, and aerial parts of Justicia species (Acanthaceae) are a potential source. We investigated the antifungal activity of extracts from stems and leaves of five Justicia species native to Northwest Argentina. The aerial parts were subjected to sequential extractions with dichloromethane, ethyl acetate, and methanol. The resulting extracts were tested by the disc diffusion method against F. graminearum strains. Only the leaf and stem extracts from J. xylosteoides displayed inhibitory effects, with the dichloromethane leaf extract as the most active. The compounds involved were identified as the lignans hinokinin, savinin, and isohibalactone. Both the dichloromethane extract and hinokinin synergised with tebuconazole, and inhibited deoxynivalenol biosynthesis. The identified compounds warrant further research as additives to azole fungicides for F. graminearum control.