Location: Corn Insects and Crop Genetics Research
2025 Annual Report
Objectives
Objective 1: Characterize the distribution of the Ga1 and Ga2 gametophytic incompatibility systems in U.S. maize breeding germplasm and the response to changes in temperature on their ability to exclude pollen.
Subobjective 1.A: Determine whether alleles capable of overcoming pollen exclusion barriers are present in the U.S. corn breeding germplasm.
Subobjective 1.B: Examine the effect of environmental factors on pollen exclusion systems.
Objective 2: Develop improved crop growth models using the Agricultural Production Systems Simulator (APSIM) for predicting variation in growth and yield among maize hybrids as affected by varying environmental and management conditions.
Subobjective 2.A: Calibrate APSIM to simulate development and growth of total dry matter, grain dry matter, and stalk dry matter across a range of multiple plant densities.
Subobjective 2.B: Test plasticity of maize sink during grain filling.
Approach
In order to use hybrid-specific crop growth models to understand factors contributing to genotype by environment interactions, replicated field trials of hybrid corn varieties will be carried out and evaluated for morphological, phonological and chemical traits. Together with environmental data, these data will be used to develop crop growth models with publicly available software. Valuable measures of agronomic performance such as grain yield of the specific hybrids in the study will be predicted. These models will be validated using actual measurements of agronomic performance and used to predict performance in additional environmental conditions. In order to understand molecular genetic control mechanism of gametophytic incompatibility, we will construct a transgene encoding ZmPME3 and use it to complement the ga1 phenotype. A second transgene will be used to mutationally inactivate ZmPME3. All transgenic lines will be evaluated for their ability to exclude unwanted pollen in replicated field trials. In addition, ZmPME will be produced in a bacterial expression system and purified. The activity of the purified protein will be characterized using pectin methylesterase activity assays and the effect of this protein on pollen tube growth will be evaluated in vitro.
Progress Report
Research in Objective 1 is related to pollen exclusion systems in Maize that are used to maintain genetic purity in corn by preventing cross-pollination between different varieties. For example, if popcorn is cross-pollinated by dent corn (a type of field corn), it cannot be marketed and thus loses its commercial value. Multiple pollen exclusion systems exist that can be used to control cross-pollination of multiple commercial corn classes. Recently, it has been discovered that "purebred" corn plants, or lines in commercial use, have genes that can overcome one of the pollen exclusion systems, which may render the system unusable. The goal of Objective 1 is to identify lines in U.S. corn breeding germplasm that carry genetic variants capable of overcoming cross-fertilization barriers. We evaluated lines from the Germplasm Enhancement of Maize (GEM) program for their ability to overcome the pollination barrier. GEM is a project to increase the diversity of U.S. maize germplasm utilized by producers, global end-users, and consumers. From previously tested lines, we identified several that overcame the barrier that will be re-tested for confirmation. Identification of lines that overcome cross-pollination barriers is critical to protect the commercial value of different market classes of corn, which directly impacts on-farm profitability.
In addition, we examined how pollen exclusion systems respond to different environmental conditions associated with different weather or growing locations. The same line of corn will prevent cross-pollination in some years and locations, but will not prevent cross-pollination in other years and or locations. It is not known under what conditions the system will prevent cross pollination or will fail to prevent cross pollination. To further investigate the variable performance of pollen exclusion, we carried out a study with lines grown in multiple locations with collaborators at North Carolina State University in Raleigh, North Carolina. Results suggest that pollen exclusion systems performed consistently across locations in some lines but not others. Additional work is planned on lines that do not maintain pollen exclusion in all conditions to further investigate the effects of individual environments on pollen exclusion.
Research outlined in Objective 2 is related to stability of maize hybrid performance across variable environmental and management conditions. Specifically, hybrids representing a wide range of genetic improvement are being grown at a range of planting densities from very low density to very high density to model changes in growth and response to environmental conditions. Two years of experimentation have been completed and the third year is in progress. Preliminary results suggest that long term efforts in maize breeding have increased overall dry-matter accumulation (which contributes to higher productivity) and improved partitioning of dry matter from stalks to grain. The observation of substantial re-partitioning of dry matter from stalk to grain coincides with long-term improvement in stalk strength, suggesting that stalks have gotten stronger while at the same time retaining less carbon. These results will generate models and more efficient breeding methods to improve maize hybrid performance and performance stability which directly impacts on-farm profitability of the maize crop.
Also as part of Objective 2, we continued to cooperate with the Genomes to Fields (G2F) Initiative by providing genetic data for genotype by environment interaction experiments at two additional field locations in 2025 and 2026. G2F is a public-private multi-state multi-institution collaboration to study maize genotype and environment interactions.
Access to data on maize hybrid performance and environmental data would not be possible without multi-institutional collaboration. Seed is being generated for seed parents of hybrids that will be grown in 2026 and 2027. This will allow us to model differences in productivity of corn hybrids and productivity in the seed parents of corn hybrids in order to better understand how to simultaneously improve hybrid grain yield and seed parent yield. Improving both seed parent yield and hybrid yield directly impacts profitability for seed companies, seed producers, and all producers of maize grain.
Accomplishments
1. Developed new methods to help maintain genetic purity in corn by preventing cross-pollination between different varieties. Popcorn hybrids contain a system that prevents cross-pollination with other varieties of corn, such as that used for animal feed. If popcorn is cross-pollinated by other varieties, it loses its commercial value and cannot be marketed. Recently, it has been discovered that some commercial lines contain a pollen-exclusion system similar to that used in popcorn that would overcome exclusion barriers in if they were used in specialty market classes such as popcorn. ARS researchers in Ames, Iowa, examined a diverse group of maize varieties and identified a group of lines that carry genetic variants of a pollen-exclusion system that would allow cross-pollination with other lines carrying that same system. These lines have been widely used in the development of commercial germplasm, and as a result the genetic variants that overcome the barrier are widespread in commercial corn germplasm. This finding is unexpected because systems used for preserving genetic purity are not widespread in commercial germplasm. It demonstrates that either alternate pollination exclusion systems will be needed for protecting additional specialty market classes or additional work will be needed to develop a strategy. This work prevents the deployment of a system that could have caused widespread failures in preventing cross-pollination in specialty market classes that would diminish on-farm profits.
Review Publications
Hintch, T., Moran Lauter, A., Kinney, S., Lubberstedt, T., Frei, U., Duangpapeng, P., Edwards, J.W., Scott, M.P. 2023. Development of maize inbred lines with elevated grain methionine concentration from a high methionine population. Crop Science. https://doi.org/10.1002/csc2.20983.
Moran Lauter, A., Holland, J.B., Scott, M.P. 2025. Analysis of Ga2 genome structure and activity reveals widespread distribution of functional loci in modern maize germplasm. G3: Genes, Genomes, Genetics. 15(5). Article jkaf035. https://doi.org/10.1093/g3journal/jkaf035.
Ruiz, A., Edwards, J.W., Castellano, M.J., Gambin, B.L., Licht, M.A., Moore, K.J., Archontoulis, S.V. 2024. Nitrogen fertilizer and plant density affect maize residue quantity and quality more than previous crop and genotype. European Journal of Agronomy. 158. Article 127215. https://doi.org/10.1016/j.eja.2024.127215.
Fakude, M., Murithi, A., Frei, U.K., Scott, M.P., Lubberstedt, T. 2024. Genome-wide association study of haploid female fertility (HFF) and haploid male fertility (HMF) in BS39-derived doubled haploid maize lines. Theoretical and Applied Genetics. 138. Article 5. https://doi.org/10.1007/s00122-024-04789-5.