Growth and Toxigenicity of A. flavus on Resistant and Susceptible Peanut Genotypes

Abstract

Aflatoxin contamination poses serious health concerns to consumers of peanut and peanut products. This study aimed at investigating the response of peanuts to Aspergillus flavus infection and aflatoxin accumulation. Isolates of A. flavus were characterised either as aflatoxigenic or non-aflatoxigenic using multiple cultural techniques. The selected isolates were used in an in vitro seed colonisation (IVSC) experiment on two A. flavus-resistant and susceptible peanut genotypes. Disease incidence, severity, and aflatoxin accumulation were measured. Genotypes differed significantly (p < 0.001) in terms of the incidence and severity of aflatoxigenic and non-aflatoxigenic A. flavus infection with the non-aflatoxigenic isolate having significantly higher incidence and severity values. There was no accumulation of aflatoxins in peanut genotypes inoculated with non-aflatoxigenic isolate, indicating its potential as a biocontrol agent. Inoculations with the aflatoxigenic isolate resulted in the accumulation of aflatoxin B1 and G1 in all the peanut genotypes. Aflatoxin B2 was not detected in ICGV−03401 (resistant genotype), while it was present and higher in Manipinta (susceptible genotype) than L027B (resistant genotype). ICGV−03401 can resist fungal infection and aflatoxin accumulation than L027B and Manipinta. Non-aflatoxigenic isolate detected in this study could further be investigated as a biocontrol agent.

Keywords: aflatoxigenic; host plant resistance and susceptible; in vitro seed colonisation; non-aflatoxigenic.

Figure 1

A. flavus colony observed under UV light at 312 nm. (A) A. flavus isolate grown on PDA fluoresces under UV light indicating aflatoxigenicity. (B) A. flavus isolate grown on PDA did not fluoresce under UV light indicating, non-aflatoxigenicity. (C) A. flavus isolate grown on YESA produced a blue fluorescence under UV light, indicating aflatoxigenicity and (D) A. flavus isolate grown on YESA did not produce a blue fluorescence under UV light, indicating non-aflatoxigenicity.

Figure 2

Colour of the underside of A. flavus colony on PDA when exposed to ammonia solution. (A) Non-aflatoxigenic A. flavus isolate before exposure and (B) non-aflatoxigenic isolate after exposure. (C) Aflatoxigenic isolate of A. flavus before exposure to Ammonia solution and (D) aflatoxigenic isolate after exposure to ammonia solution.

Figure 3

Radial growth of aflatoxigenic (A) and non-aflatoxigenic (NA) A. flavus on PDA. Error bars represent standard errors of means. A2—Aflatoxigenic isolate 2, A8—Aflatoxigenic isolate 8, NA11—Non-aflatoxigenic isolate 11, NA12—Non-aflatoxigenic isolate 12.

Figure 4

Area under disease progress curve (AUDPC) value for aflatoxigenic and non-aflatoxigenic A. flavus isolates on PDA. Error bars represent standard errors of means. A2—Aflatoxigenic isolate 2, A8—Aflatoxigenic isolate 8, NA11—Non-aflatoxigenic isolate 11, NA12—Non-aflatoxigenic isolate 12.

Figure 5

Incidence of aflatoxigenic and non-aflatoxigenic A. flavus on resistant peanut genotypes (ICGV–03401 and L027B) and susceptible peanut genotype (Manipinta). Error bars represent standard errors of means.

Figure 6

Severity of aflatoxigenic and non-aflatoxigenic A. flavus on resistant peanut genotypes (ICGV–03401 and L027B) and susceptible peanut genotype (Manipinta). Error bars represent standard errors of means.

Figure 7

Chromatogram (A) shows the peaks of aflatoxin B₁, B₂, and G₁ in peanut genotype L027B, chromatogram (B) indicates the peaks of aflatoxin B₁ and G₁ in ICGV–03401, chromatogram (C) represents the peaks of aflatoxin B₁, B₂, and G₁ in Manipinta infested with aflatoxigenic isolate. The chromatogram (D) shows the non-detection of aflatoxin accumulation in peanut genotypes L027B, ICGV–03401, and Manipinta infested with non-aflatoxigenic isolate. Red line denotes the peaks, while black line refers to the baseline.

Figure 8

Chromatogram represents the aflatoxin standards used in the HPLC analysis. G₁—Aflatoxin G₁, G₂—Aflatoxin G₂, B₁—Aflatoxin B₁ and B₂—Aflatoxin B₂. Red line denotes the peaks, while black line refers to the baseline.