The role of ear environment in postharvest susceptibility of maize to toxigenic Aspergillus flavus

Authors: MUTIGA, SAMUEL - Cornell University; CHEPKWONY, NELSON - Cornell University; HOEKENGA, OWEN - Cayuga Genetics Consulting Group, Llc; Flint-Garcia, Sherry; NELSON, REBECCA - Cornell University

Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2018
Publication Date: 2/1/2019
Citation: Mutiga, S.K., Chepkwony, N., Hoekenga, O.A., Flint-Garcia, S.A., Nelson, R.J. 2019. The role of ear environment in postharvest susceptibility of maize to toxigenic Aspergillus flavus. Plant Breeding. 138(1):38-50. https://doi.org/10.1111/pbr.12672.
DOI: https://doi.org/10.1111/pbr.12672

Interpretive Summary: Yield losses occur due to microbial and insect pests during the entire life cycle of crop plants – beginning with germination, throughout the growth phase, and during harvest. Losses can also continue into the grain storage period, and is a severe problem under specific storage conditions worldwide. In corn, the fungus Aspergillus flavus colonizes grain in the field, and after harvest can spread throughout the entire grain lot during storage. This fungus can produce aflatoxin, which poses a major threat to food safety and security around the world. We wanted to determine the nature of post-harvest fungal spread and aflatoxin production in stored maize grains: how important is the field environment in which the grain was produced compared to the corn variety? Our study showed that both the corn variety and the production environment, as well as an interaction between corn variety and environment, all contribute to fungal spread and aflatoxin production. This combination of environment and variety factors adds another layer of complexity to the corn-Aspergillus-aflatoxin system, and leads to difficulty in predicting whether small amounts of field-infected seed will cause an entire storage lot to become infected and unsafe for human and animal consumption. The results of this study will be used by corn breeders and geneticists who are developing corn which is resistant to the fungus and limits aflatoxin production.

Technical Abstract: Colonization of maize by Aspergillus flavus can cause quality loss and aflatoxin accumulation. Aflatoxin is a threat to the health of maize consumers globally. Post-harvest resistance to maize colonization by aflatoxigenic fungi can enhance food safety. We used a kernel screening assay to assess the relative importance of genetic and environmental factors in the vulnerability of mature maize grain to colonization by A. flavus and aflatoxin accumulation. Kernels of 26 diverse maize inbred lines that had been grown in seven environments, as well as 190 lines of the Intermated B73 x Mo17 (IBM) population grown in one location in the United States, were inoculated with an aflatoxigenic strain of A. flavus and incubated in the dark at 30oC for 6 days. Percent kernel colonization, fungal sporulation, and aflatoxin were significantly influenced by the genotypes of the inbred lines, the environment where the parent plant had been grown (“ear environment”), and the genotype and the ear environment (GxE) interactions. Kernel colonization was significantly correlated with sporulation in all environments. Toxin content was positively correlated with kernel colonization for two and with sporulation for all ear environments. Significant negative correlations were observed between the IBM grain sulfur content and kernel colonization or aflatoxin. Similarly, magnesium were negatively correlated with kernel colonization. Findings of this study suggest that susceptibility of stored grain to A. flavus and aflatoxin is influenced by the nutritional content of the grain, a factor that is modulated by the environment in which the parental line is grown.