Dissecting symptomatology and fumonisin contamination produced by Fusarium verticillioides in maize ears

Authors: MORALES, LAURA - Cornell University; MARINO, THIAGO - North Carolina State University; WENNDT, ANTHONY - Cornell University; FOUTS, JULIA - Cornell University; Holland, Jim - Jim; NELSON, REBECCA - Cornell University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2018
Publication Date: 11/5/2018
Citation: Morales, L., Marino, T.P., Wenndt, A.J., Fouts, J.Q., Holland, J.B., Nelson, R.J. 2018. Dissecting symptomatology and fumonisin contamination produced by Fusarium verticillioides in maize ears. Phytopathology. 108:1475-1485.

Interpretive Summary: The fungus Fusarium verticillioides can infect maize ears, contaminating the grain with mycotoxins, including fumonisins. This global public health threat can be managed by breeding maize varieties that are resistant to colonization by F. verticillioides and by sorting grain after harvest to reduce fumonisin levels in food systems. In this study, we compared two different methods of inoculating maize breeding lines to evaluate their levels of resistance to this fungal disease. Results indicate that the two different methods reveal different forms of resistance in the host plants, suggesting that breeders use both methods at some point during the evaluation of their breeding lines in order to select the most consistently resistant corn plants.

Technical Abstract: The fungus Fusarium verticillioides can infect maize ears, contaminating the grain with mycotoxins, including fumonisins. This global public health threat can be managed by breeding maize varieties that are resistant to colonization by F. verticillioides and by sorting grain after harvest to reduce fumonisin levels in food systems. Here we employed two F. verticillioides inoculation techniques representing distinct infection pathways to dissect ear symptomatology and morphological resistance mechanisms in a diverse panel of maize inbred lines. The “point” method involved penetrating the ear with a spore-coated toothpick, and the “inundative” method introduced a liquid spore suspension under the husk of the ear. We evaluated quantitative and qualitative indicators of external and internal symptom severity as low-cost proxies for fumonisin contamination, and found that kernel bulk density was predictive of fumonisin levels (78-84% sensitivity; 97-99% specificity). Inundative inoculation resulted in greater disease severity and fumonisin contamination than point inoculation. We also found that the two inoculation methods implicated different ear tissues in defense, with cob morphology being a more important component of resistance under point inoculation. Across both inoculation methods, traits related to cob size were positively associated with disease severity and fumonisin content. Our work demonstrates that (1) the use of diverse modes of inoculation is necessary for combining complementary mechanisms of genetic resistance; (2) kernel bulk density can be used effectively as a proxy for fumonisin levels, and (3) trade-offs may exist between yield potential and resistance to fumonisin contamination.