Effects of artificial inoculation on trait correlations with resistance to Fusarium ear rot and fumonisin contamination in maize

Authors: BUTOTO, ERIC - North Carolina State University; MARINO, THIAGO - North Carolina State University; Holland, Jim - Jim

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2021
Publication Date: 5/1/2021
Citation: Butoto, E., Marino, T., Holland, J.B. 2021. Effects of artificial inoculation on trait correlations with resistance to Fusarium ear rot and fumonisin contamination in maize. Crop Science. 61:2522-2533. https://doi.org/10.1002/csc2.20551.
DOI: https://doi.org/10.1002/csc2.20551

Interpretive Summary: Fusarium ear rot is a fungal disease of corn that reduces yield and grain quality. The fungus can also produce a mycotoxin, fumonisin, that is associated with health concerns in animals and people. Breeding for resistance to Fusarium ear rot and fumonisin contamination in maize is labor-intensive, time-consuming, and expensive. The objective of this study is to explore three possible ‘shortcuts’ to improve the efficiency of breeding for resistance to these aspects of ear rot disease. One possibility is relying on natural instead of artificial inoculation of the fungus that causes the disease, which would make selection experiments easier to conduct and could allow breeders to increase the number of lines they screen. However, our results show that this would not be a good idea, since artificial inoculation dramatically increases the reliability of visual scores of ear rot and also for fumonisin contamination. A second shortcut we investigated was selecting inbred lines directly instead of evaluating their hybrids (which takes an additional generation and a lot of work); we found that this shortcut is a good idea. Resistance observed in inbreds is highly correlated with resistance observed in hybrids made from those inbreds. The third shortcut is to measure grain test weight (the weight per volume of grain) of each line that has been inoculated with the fungus. We also found that test weight measured under these conditions is highly correlated with disease resistance in the hybrids of those inbreds. This suggests that breeders can measure test weight on inoculated inbreds (which can be faster and more accurate than visual scoring the disease), and make improvements in resulting hybrids.

Technical Abstract: Breeding for resistance to Fusarium ear rot (FER) and fumonisin (FUM) contamination in maize is labor-intensive, time-consuming, and expensive. The objective of this study is to explore three possible ‘shortcuts’ to improve the efficiency of breeding for resistance to FER and FUM: relying on natural instead of artificial inoculation of Fusarium verticillioides, selecting inbred lines per se instead of topcross hybrids, and using grain test weight (TW) as an indirect selection criterion. We selected the 27 most resistant and 26 most susceptible S0:1 lines from the third cycle of a broad-sense recurrent selection population and topcrossed them to a common inbred line. The resulting topcross hybrids were evaluated in three North Carolina environments under artificial and natural inoculation of F. verticillioides. The entry-mean heritabilities for FER and FUM are considerably reduced under natural conditions compared to under artificial inoculation; therefore artificial inoculation should be practiced for efficient selection for resistance. We found a high correlation between FER and FUM contents of S0:1 lines per se and their topcross hybrids, suggesting that selection among early generation inbred lines per se is an efficient method to improve resistance in their topcross hybrids. TW of inoculated S0:1 lines per se was strongly positively correlated with FER or FUM of their their topcross hybrids, suggesting that TW can be utilized as an indirect selection criterion to improve resistance to FER and FUM contamination.