Influence of Wounding and Temperature on Resistance of Maize Landraces From Mexico to Aflatoxin Contamination.

Alejandro Ortega-Beltran,Peter J Cotty

doi:10.3389/fpls.2020.572264

Abstract

Maize is a staple for billions across the globe. However, in tropical and sub-tropical regions, maize is frequently contaminated with aflatoxins by Aspergillus section Flavi fungi. There is an ongoing search for sources of aflatoxin resistance in maize to reduce continuous exposures of human populations to those dangerous mycotoxins. Large variability in susceptibility to aflatoxin contamination exists within maize germplasm. In Mexico, several maize landrace (MLR) accessions possess superior resistance to both Aspergillus infection and aflatoxin contamination but their mechanisms of resistance have not been reported. Influences of kernel integrity on resistance of four resistant and four susceptible MLR accessions were evaluated in laboratory assays. Wounds significantly (P < 0.05) increased susceptibility to aflatoxin contamination even when kernel viability was unaffected. Treatments supporting greater A. flavus reproduction did not (P > 0.05) proportionally support higher aflatoxin accumulation suggesting differential influences by some resistance factors between sporulation and aflatoxin biosynthesis. Physical barriers (i.e., wax and cuticle) prevented both aflatoxin accumulation and A. flavus sporulation in a highly resistant MLR accession. In addition, influence of temperature on aflatoxin contamination was evaluated in both viable and non-viable kernels of a resistant and a susceptible MLR accession, and a commercial hybrid. Both temperature and living embryo status influenced (P < 0.05) resistance to both aflatoxin accumulation and A. flavus sporulation. Lower sporulation on MLR accessions suggests their utilization would result in reduced speed of propagation and associated epidemic increases in disease both in the field and throughout storage. Results from the current study should encourage researchers across the globe to exploit the large potential that MLRs offer to breed for aflatoxin resistant maize. Furthermore, the studies provide support to the importance of resistance based on the living host and maintaining living status to reducing episodes of post-harvest contamination.

Highlights

Aflatoxins are highly toxic and carcinogenic mycotoxins produced by Aspergillus flavus and closely-related fungi (Cotty et al, 1994)
Aflatoxin B1 produced by A. flavus AF13 was significantly (P < 0.0001) lower in the four R-maize landrace (MLR) than in S-MLRs and P33B50, as expected (Table 1)
We examined susceptibility of maize kernels to aflatoxin accumulation at three different temperatures using a kernel screening assay (KSA)

Summary

Introduction

Aflatoxins are highly toxic and carcinogenic mycotoxins produced by Aspergillus flavus and closely-related fungi (Cotty et al, 1994). These potent toxins are detrimental to both human and animal health and one of them, aflatoxin B1, is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) (JECFA, 2018). Aflatoxin exposure is most severe in emerging and developing nations where legislation is poorly enforced or nonexistent (Resnik et al, 1995; Bandyopadhyay et al, 2016; Seetha et al, 2017; Logrieco et al, 2018). Because aflatoxin contamination of maize has little impact on yield, contamination may not attract farmer attention in the absence of strictly enforced and extensive awareness training (Bandyopadhyay et al, 2016; Udomkun et al, 2017)

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