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.