Location: Corn Insects and Crop Genetics Research
2022 Annual Report
Objectives
Objective 1: Develop improved maize phenotyping methods based on process-based crop growth models and high throughput phenotyping methods.
Subobjective 1.1: Develop and validate crop growth model calibrations for diverse maize hybrids to predict maize hybrid performance across diverse environments.
Subobjective 1.2: Evaluate high throughput biochemical and metabolic assays for calibration of crop growth models and prediction of maize grain yield.
Subobjective 1.3: Evaluate remote sensing approaches for improving prediction of maize performance and crop growth model calibration.
Objective 2: Understand the molecular genetic control of gametophytic incompatibility.
Subobjective 2.1: Determine if ZmPme3 complements the ga1 allele to restore the female function of Ga1-s.
Subobjective 2.2: Determine the biochemical mechanism of pollen exclusion by the Ga1 system using E. coli expressed ZmPME3.
Subobjective 2.3: Identify binding partners of ZmPME3.
Approach
In order to used 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 to 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
As part of the congressionally mandated agreement with Michael Fields Agricultural Institute (MFAI), ARS scientists in Ames, Iowa made crosses among the best maize lines from USDA and MFAI. These hybrids were planted this year for evaluation. Scientists from ARS and MFAI also started work on joint development of a near infrared reflectance (NIR) calibration for prediction of the nutritionally important amino acid methionine. MFAI and ARS obtained the same model of NIR spectrometer, thus jointly developed calibrations will be useful to both organizations. This calibration will allow development of corn varieties for the Northern Corn Belt that are particularly well-suited to use in chicken feed.
In research funded by the National Institute of Food and Agriculture’s Organic Agriculture Research Extension Initiative (NIFA-OREI), ARS scientists in Ames, Iowa are trying to reduce the time required for each breeding cycle, which will increase the rate of progress in breeding programs. To do this, we are developing a rapid-cycle breeding method by combining two new breeding technologies (doubled haploids and genomic selection). The genetic stocks that will be required to do this research have been prepared. A genetic locus conferring gametophytic incompatibility and a genetic locus conferring spontaneous haploid genome doubling were back-crossed into elite inbred maize lines developed in earlier research efforts. The elite lines have been genotyped and phenotypic data from experimental hybrids in organic and conventional environments has been collected. With the completion of this work, we can begin testing our rapid-cycle breeding method for development of improved varieties.
Puramaize is the trademark for maize hybrids that are marketed to organic corn growers and contain a genetic locus called Gametophyte-factor 1 (Ga1), that reduces contamination by pollen from genetically modified organisms (GMO). The Ga1 system has been used in popcorn for decades to reduce unwanted pollen contamination. ARS scientists in Ames, Iowa compared the effectiveness of the Ga1 system in Puramaize and popcorn and found that while popcorn is slightly better overall, both are highly effective at preventing unwanted pollinations compared to hybrids that do not have the Ga1 system. Differences in effectiveness were attributed to genes that modify the effect of the Ga1 system, rather than differences in the Ga1 system itself. This information is important for making regulatory decisions regarding claims about GMO content. Currently Puramaize and Popcorn are subject to different GMO testing requirements. These data suggest that with adequate field-testing during development of Puramaize hybrids, they could be subject to the same GMO testing requirements as popcorn. This would reduce the production cost of organic corn and organic corn products. This information has been submitted for publication in a peer reviewed journal.
As part of a cooperative agreement with the Iowa Corn Promotion Board, ARS scientists in Ames, Iowa evaluated diverse maize hybrids at four Iowa locations in the 2021 growing season. Data were collected on nine agronomic traits. Agronomic data in addition to weather data and management data were submitted to the Genomes to Fields (G2F) Initiative. The G2F initiative is a multi-state, multi-institution initiative designed to foster collaboration and improve understanding of genomic control of complex traits. Collaborators in G2F grew diverse hybrids across many diverse environments in order to understand how diverse hybrids perform across a range of very different environments. The work is continuing with diverse hybrids again planted in four locations in 2022.
As part of a collaboration with scientists from Brigham Young University, ARS scientists in Ames, Iowa produced seed of maize 64 hybrids with widely varying stalk strength. The hybrids have been planted in three Iowa locations at three plant densities. The hybrids will be used to test a novel approach to testing stalk strength using devices developed by scientists at Brigham Young University to measure stalk strength. The devices determine the amount of force required to break the stalk.
ARS scientists in Ames, Iowa have continued to evaluate a set of 12 maize hybrids for calibration of crop growth models. Previously, the scientists calibrated models in the Agricultural Production Systems Simulator (APSIM) software platform based on intensive phenotyping efforts carried out over two years. These model calibrations were somewhat limited because they were based on only two environments. Therefore, additional data on these hybrids was collected in 2021 and will be collected in 2022. The additional data will be used to update calibrations and to evaluate the extent to which environmental variation affects calibration of underlying hybrid-specific model parameters.
Accomplishments
1. Enhancements in maize crop growth models improve their utility in predicting performance of maize hybrids. Predicting differences in maize hybrid performance among locations and years remains a challenge for producers, breeders, and researchers. Crop Growth models have become more widely used to simulate production systems to predict effects of weather, management, and to a more limited extent, crop cultivars. In maize research, model calibrations have not been made available or tested to determine to what extent crop growth models can predict grain yield differences among a set of maize hybrids adapted to a common region. ARS researchers in Ames, Iowa, have completed calibration and validation of crop growth models for 12 publicly available maize hybrids. Model calibration and validation demonstrated that crop growth models predict nearly 40-58% of grain yield differences among sets of maize hybrids solely on the basis of physiological characteristics of hybrids combined with weather, soil, and management data in some years and locations. These results demonstrate that crop growth models have potential to become a valuable management and prediction tool to benefit researchers, breeders, and producers.
Review Publications
Goncalves Dos Santos, L., Verzegnazzi, A.L., Edwards, J.W., Frei, U.K., Boerman, N.A., Tenello Zuffo, L., Pires, L.M., De La Fuente, G.N., Lubberstedt, T. 2022. Usefulness of temperate-adapted maize lines developed by doubled haploid and single-seed descent methods. Journal of Theoretical and Applied Genetics. 135:1829-1841. https://doi.org/10.1007/s00122-022-04075-2.
Nankar, A.N., Scott, M.P., Pratt, R.C. 2020. Compositional analyses reveal relationships among components of blue maize grains. Plants. 9(12). Article 1775. https://doi.org/10.3390/plants9121775.
Weldekidan, T., Manching, H., Choquette, N., de Leon, N., Flint-Garcia, S.A., Holland, J.B., Lauter, N.C., Murray, S.C., Xu, W., Goodman, M., Wisser, R.J. 2022. Registration of tropical populations of maize selected in parallel for early flowering time across the United States. Journal of Plant Registrations. 16(1):100-108. https://doi.org/10.1002/plr2.20181.
