Inhibitory effects of respiration inhibitors on aflatoxin production

Abstract

Aflatoxin production inhibitors, which do not inhibit the growth of aflatoxigenic fungi, may be used to control aflatoxin without incurring a rapid spread of resistant strains. A respiration inhibitor that inhibits aflatoxin production was identified during a screening process for natural, aflatoxin-production inhibitors. This prompted us to evaluate respiration inhibitors as potential aflatoxin control agents. The inhibitory activities of four natural inhibitors, seven synthetic miticides, and nine synthetic fungicides were evaluated on aflatoxin production in Aspergillus parasiticus. All of the natural inhibitors (rotenone, siccanin, aptenin A5, and antimycin A) inhibited fungal aflatoxin production with IC50 values around 10 µM. Among the synthetic miticides, pyridaben, fluacrypyrim, and tolfenpyrad exhibited strong inhibitory activities with IC50 values less than 0.2 µM, whereas cyflumetofen did not show significant inhibitory activity. Of the synthetic fungicides, boscalid, pyribencarb, azoxystrobin, pyraclostrobin, and kresoxim-methyl demonstrated strong inhibitory activities, with IC50 values less than 0.5 µM. Fungal growth was not significantly affected by any of the inhibitors tested at concentrations used. There was no correlation observed between the targets of respiration inhibitors (complexes I, II, and III) and their IC50 values for aflatoxin-production inhibitory activity. This study suggests that respiration inhibitors, including commonly used pesticides, are useful for aflatoxin control.

Figure 1

Effects of natural respiration inhibitors, rotenone (a); siccanin (b); atpenin A5 (c); and antimycin A (d), on aflatoxin (total aflatoxins B₁ and G₁) production (gray bars) and mycelial weight (black triangles) of A. parasiticus. n = 4–5, ** p < 0.01; * p < 0.05, vs. control.

Figure 2

Effects of synthetic miticides, pyridaben (a); tolfenpyrad (b); mepronil (c); fluacrypyrim (d); acequinocyl (e); and bifenazate (f), on aflatoxin (total aflatoxins B₁ and G₁) production (gray bars) and mycelial weight (black triangles) of A. parasiticus. n = 4; * p < 0.05, vs. control.

Figure 3

Effects of synthetic fungicides, boscalid (a); pyribencarb (b); cyazofamid (c); pyraclostrobin (d); kresoxym-methyl (e); azoxystrobin (f); trifloxystrobin (g); picoxystrobin (h); and metominostrobin (i), on aflatoxin (total aflatoxins B₁ and G₁) production (blue bars) and mycelial weight (black triangles) of A. parasiticus. n = 4–5; ** p < 0.01; * p < 0.05, vs. control.