Differential Corn ( Zea mays ) Kernel Infection and Metabolism by Two Aspergillus flavus Strains

ABSTRACT Aspergillus flavus infection of corn ( Zea mays ) is a major agronomic concern due to contamination with acutely toxic and carcinogenic aflatoxins. A. flavus populations are very diverse; however, more than 70% of corn isolates produce large sclerotia. There is limited research investigating corn infection by different A. flavus strains. This study tracked corn kernel infection by a small sclerotial strain, Af70‐GFP (S), and a large sclerotial strain, Tox4‐RFP (L), that were engineered to express green and mCherry red fluorescent proteins, respectively. Fluorescence, aflatoxin and A. flavus DNA were assessed to track fungal infection. Near‐infrared light spectroscopy was used to measure kernel nutrient composition. Af70‐GFP (S) was able to establish kernel infection earlier than Tox4‐RFP (L) as measured by fluorescence and droplet digital PCR (ddPCR); Af70‐GFP (S) also produced aflatoxin earlier in infection and in greater quantities. Protein, fat and starch content decreased in corn kernels with longer infection. Af70‐GFP (S) infection resulted in a reduction in kernel starch content, and Tox4‐RFP (L) reduced protein and fat content more than Af70‐GFP (S). Increased starch metabolism probably resulted in greater aflatoxin production by Af70‐GFP (S). This research suggests that A. flavus strains may differ in their abilities to infect corn. Hence, a greater diversity of A. flavus should be assessed in future studies for their virulence to assist in improving biocontrol and resistance technologies.