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

Two isolates of Colletotrichum musae (CM100 and CM103) which differed significantly in their sensitivity to the fungicides thiabendazole (TBZ) and imazalil were grown on malt extract agar amended with the following antioxidants: ascorbic acid, benzoic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene, dimethyl sulphoxide, propionic acid, propyl gallate (PG), propyl paraben (PP) and thiourea. The compounds showing the greatest antifungal activity were BHA, benzoic acid, PG and PP. At concentrations of 15 mM or less, these chemicals inhibited conidial germination (at 72 h) and mycelial 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 imazalil (1.8 muM) completely prevented mycelial growth and germination of the two isolates tested in vitro and showed some synergism when combined at even lower concentrations of BHA. BHA, PP and benzoic acid, in combination with each other and with imazalil and TBZ, applied to banana stalk tissues and crowns previously inoculated with C. musae, were less effective at controlling the fungus in vivo compared with inhibiting mycelial growth and conidial germination in vitro. BHA at 5 mM inhibited fungal growth at 25 degreesC 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 imazalil (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 food-grade chemical, might have the potential to enhance the activity of fungicides currently used to control C. musae on bananas, allowing lower concentrations of fungicide to be used.