Sugar beet waste and its component ferulic acid inhibits external mycelium of arbuscular mycorrhizal fungus

► Sugar beet waste (SB) inhibits in vitro growth of AM fungal mycelium. ► Inhibition disappears if SB is first fermented by Aspergillus. ► Water extracts of SB and fermented product were analyzed by GC-MS. ► Ferulic acid was present in SB and absent in fermented product. ► Ferulic acid also inhibits AM fungal mycelium and is one adverse compound of SB.