Plant nutrition influences resistant maize defense responses to the fall armyworm (Spodoptera frugiperda)

Authors: Mason, Charles; RAY, SWAYAMJIT - Cornell University; DAVIDSON-LOWE, ELIZABETH - Orise Fellow; ALI, JARED - Pennsylvania State University; LUTHE, DAWN - Pennsylvania State University; FELTON, GARY - Pennsylvania State University

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2022
Publication Date: 2/25/2022
Citation: Mason, C.J., Ray, S., Davidson-Lowe, E., Ali, J., Luthe, D., Felton, G. 2022. Plant nutrition influences resistant maize defense responses to the fall armyworm (Spodoptera frugiperda). Frontiers in Ecology and Evolution. 10. Article 844274. https://doi.org/10.3389/fevo.2022.844274.
DOI: https://doi.org/10.3389/fevo.2022.844274

Interpretive Summary: Plants experience simultaneous challenges, and need to balance resources. Understanding how fertilization and plant resistance intersect can lead to new management practices and better use of resources. We evaluated how resistant maize cultivars mount defense responses to fertilization and fall armyworm herbivory. In our experiments, both plant genotypes increased their defenses in response to herbivore pressure, but their expression levels varied between different fertilization treatments. Our results data suggest that defenses can be reduced by a lack of fertilization, but only in certain genotypes. Additionally, we found that not all defenses respond similarly, suggesting a need to evaluate how herbivory and fertilization impact resistant plant species and cultivars on a case-by-case bases.

Technical Abstract: Plants are often confronted by different groups of herbivores, which threaten their growth and reproduction. However, plants are capable of mounting defenses against would-be attackers which may be heightened upon attack. Resistance to insects often varies among plant species, with different genotypes exhibiting unique patterns of chemical and physical defenses. Within this framework, plant’s access to nutrients may be critical for maximal functioning of resistance mechanisms and likely differ among plant genotypes. In this study, we aimed to test the hypothesis that access to nutrition would alter the expression of plant resistance to insects and would alter insect performance in a manner consistent with fertilization regime. We used two maize (Zea mays) genotypes possessing different levels of resistance and the fall armyworm (Spodoptera frugiperda) as model systems. Plants were subjected to three fertilization regimes prior to assessing insect-mediated responses. Upon reaching V4 stage, maize plants were separated into two groups, one of which was infested with fall armyworm larvae to induce plant defenses. Plant tissue was collected and used in insect bioassays and to measure the expression of defense-related genes and proteins. Insect performance differed between the two plant genotypes substantially. For each genotype, fertilization altered larval performance, where lower fertilization rates hindered larval growth. Induction of plant defenses by prior herbivory substantially reduced naïve fall armyworm growth in both genotypes. The interactive effects between fertilization and induced defenses were complex, with low fertilization reducing induced defenses in the resistant maize. Gene and protein expression patterns differed between the genotypes, with herbivory often increasing expression, but differing between fertilization. The soluble protein concentrations did not change across fertilization levels but was higher in the susceptible maize genotype. These results demonstrate the malleability of plant defenses and the cascading effects of plant nutrition on insect herbivory.