Control of the anthracnose pathogen of banana (Colletotrichum musae) usingantioxidants alone and in combination with thiabendazole or imazalil

Two isolates of Colletotrichum musae (CM100 and CM103) which differed signi ficantly in their sensitivity to the fungicides thiabendazole (TBZ) and ima zalil were grown on malt extract agar amended with the following antioxidan ts: ascorbic acid, benzoic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene, dimethyl sulphoxide, propionic acid, propyl gallate (PG), p ropyl paraben (PP) and thiourea. The compounds showing the greatest antifun gal activity were BHA, benzoic acid, PG and PP. At concentrations of 15 mM or less, these chemicals inhibited conidial germination (at 72 h) and mycel ial growth (by day 14) of isolate CM100 and gave high levels of inhibition of isolate CM103. Combinations of low concentrations of BHA (0.5 mM) and im azalil (1.8 muM) completely prevented mycelial growth and germination of th e two isolates tested in vitro and showed some synergism when combined at e ven lower concentrations of BHA. BHA, PP and benzoic acid, in combination w ith each other and with imazalil and TBZ, applied to banana stalk tissues a nd crowns previously inoculated with C. musae, were less effective at contr olling the fungus in vivo compared with inhibiting mycelial growth and coni dial germination in vitro. BHA at 5 mM inhibited fungal growth at 25 degree sC by 35-41%. When BHA (5 mM) was combined with imazalil (0.45 mM), better control (63-80% inhibition) of simulated crown rot was achieved than when i mazalil (1.78 mM) or TBZ (2.46 mM) were applied on their own (53-58% and 43 -54% inhibition, respectively). The results suggest that BHA, which is a fo od-grade chemical, might have the potential to enhance the activity of fung icides currently used to control C. musae on bananas, allowing lower concen trations of fungicide to be used.