Antagonism of nonaflatoxigenic Aspergillus flavus isolated from peanuts against aflatoxigenic A. flavus growth and aflatoxin B1 production in vitro

Abstract

Aspergillus section Flavi constitutes several species of opportunistic fungi, notable among them are A. flavus and A. parasiticus, capable of surviving harsh conditions and colonizing a wide range of agricultural products pre- and postharvest. Physical and chemical control methods are widely applied in order to mitigate the invasion of A. flavus in crops. However, physical control is not suitable for large scale and chemical control often leads to environmental pollution, whereas biological control offers a safer, environmentally friendly, and economical alternative. The present study aimed to investigate the antagonism of several non-aflatoxigenic A. flavus strains against the aflatoxigenic ones in vitro (semisynthetic peanut growth medium; MPA) in terms of colony growth rate and AFB₁ inhibition. Different peanut concentrations were used to obtain the optimum peanut concentration in the formulated growth medium. A dual culture assay was performed to assess the antagonism of nonaflatoxigenic strains against the aflatoxigenic ones. Results revealed that 9% MPA exhibited the highest growth and AFB₁ inhibition by nonaflatoxigenic strains. It was also found that different nonaflatoxigenic strains exhibited different antagonism against the aflatoxigenic ones which ranged from 11.09 ± 0.65% to 14.06 ± 0.14% for growth inhibition, and 53.97 ± 2.46% to 72.64 ± 4.54% for AFB₁ inhibition. This variability could be due to the difference in antagonistic metabolites produced by different nonaflatoxigenic strains assessed in the present study. Metabolomics study to ascertain the specific metabolites that conferred the growth and aflatoxin inhibition is ongoing.

Keywords: Aspergillus flavus; aflatoxigenic; aflatoxin B1; biocontrol; colony growth rate; non‐aflatoxigenic.

FIGURE 1

Hyphal expansion of aflatoxigenic Aspergillus flavus (strain A8R; right) cocultivated with nonaflatoxigenic A. flavus (strain A121R; left) on 90 mm Ø potato dextrose agar (PDA) and milled‐peanut agar (MPA) plates at different peanut concentrations (3, 5, 7, 9, 10, 20, and 30% w/v). Plates were incubated at 30°C for 7 days, and hyphal expansion was recorded daily

FIGURE 2

Colony growth rate inhibition (%) of aflatoxigenic Aspergillus flavus (strain A8R) cocultivated with nonaflatoxigenic A. flavus (strain A121R) on potato dextrose agar (PDA) and milled‐peanut agar (MPA) plates at different peanut concentrations (3, 5, 7, 9, 10, 20, 30% w/v), and incubated at 30°C for 7 days. Data are means of triplicate (n = 3) with bars indicating a standard error (SE). Small letters indicate a significant difference (p < .05) using least significant difference (LSD)

FIGURE 3

Aflatoxin B1 inhibition (%) of aflatoxigenic Aspergillus flavus (strain A8R) cocultivated with nonaflatoxigenic A. flavus (strain A121R) on potato dextrose agar (PDA) and milled‐peanut agar (MPA) plates at different peanut concentrations (3, 5, 7, 9, 10, 20, and 30% w/v), and incubated at 30°C for 7 days. Data are means of triplicate (n = 3) with bars indicating a standard error (SE). Small letters indicate a significant difference (p < .05) using least significant difference (LSD)

FIGURE 4

Hyphal expansion of aflatoxigenic Aspergillus flavus (strain A8R; right) cocultivated with different nonaflatoxigenic A. flavus strains (left) on 90 mm Ø 9% milled‐peanut agar (9% MPA) plates. Plates were incubated at 30°C for 7 days, and hyphal expansion was recorded daily

FIGURE 5

Colony growth rate inhibition (%) of aflatoxigenic Aspergillus flavus (strain A8R) cocultured with different nonaflatoxigenic A. flavus strains on potato dextrose agar (PDA) and 9% milled‐peanut agar (9% MPA) plates, incubated at 30°C for 7 days. Data are means of triplicate (n = 3) with bars indicating a standard error (SE). Capital letters indicate a significant difference (p < .05) between 9% MPA plates using least significant difference (LSD). Small letters indicate a significant difference (p < .05) between PDA plates using least significant difference (LSD)

FIGURE 6

Aflatoxin B₁ inhibition (%) of aflatoxigenic Aspergillus flavus (strain A8R) cocultured with different nonaflatoxigenic A. flavus strains on potato dextrose agar (PDA) and 9% milled‐peanut agar (9% MPA) plates, incubated at 30°C for 7 days. Data are means of triplicate (n = 3) with bars indicating a standard error (SE). Capital letters indicate a significant difference (p < .05) between 9% MPA plates using least significant difference (LSD). Small letters indicate a significant difference (p < .05) between PDA plates using least significant difference (LSD)