Location: Plant Introduction Research
2019 Annual Report
Objectives
Objective 1: Manage and coordinate the Midwestern component of a multi-year, multi-site, cooperative program of maize genetic resource evaluation, genetic enhancement, inbred line development, and information sharing which will broaden the genetic base for U.S. maize.
Sub-objectives: 1A. Coordinate and manage in-kind support for evaluation, development, and genetic enhancement of GEM germplasm.
1B. Manage GEM field nurseries, germplasm exchange, and seed inventories to ensure that new sources of germplasm and information reach stakeholders annually.
1C. Implement database evaluation enhancements to identify GEM lines best suited for particular uses.
Objective 2: Evaluate a wide diversity of temperate, subtropical, and tropical maize genetic resources for adaptation, yield, resistance to ear, stalk, and foliar diseases, tolerance to environmental extremes, and selected value-added, product quality traits. Record and disseminate evaluation data via the GEM database, GEM website, GRIN-Global and other data sources.
Sub-objectives: 2A. Evaluate 50-100 maize exotic breeding crosses and new sources of exotic germplasm annually for their adaptation to Midwestern U.S.; identify favorable agronomic traits; choose and prioritize germplasm for incorporation into breeding programs.
2B. With public and private-sector cooperators, evaluate maize germplasm for globally important leaf and stalk rot diseases, reduced ear mold and mycotoxin production, abiotic stress tolerance, host plant resistance to corn rootworm (CRW), multiple pest resistance for above ground insects, and key value-added traits such as highly digestible starch and resistant starch.
Objective 3: Breed and release maize populations and inbred lines with 25% subtropical-tropical/75% temperate pedigrees which contribute to U.S. maize more diverse genetic resistance to diseases, tolerance to environmental extremes, higher yield, unique product qualities, other valuable new traits, or which enable maize trait analysis and allelic diversity research.
Sub-objectives: 3A. Develop and release a novel set of “adapted” maize races resulting from the allelic diversity (AD) project as tools for gene discovery and genomic research.
3B. Develop and release germplasm with key traits, such as reduced mycotoxin level and biotic stress resistance. Disseminate germplasm information.
3C. Evaluate released lines to determine exotic genome contributions and identify unique disease and insect resistance genes.
Approach
Obj 1: Extensive collaborations with the private, public and international sectors will be initiated to broaden the germplasm base and develop useful germplasm. ARS will serve as liaison for collaborators and the Technical Steering Group (TSG), selects germplasm, facilitates germplasm acquisition and stakeholder interactions, arranges for in-kind-support, information sharing, technology transfer in the form of new germplasm and associated information, and establishes and manages nurseries and yield trials. Multiple sites will serve nurseries, observations, crossing blocks, yield trials, and stress resistance evaluations. Companies participating in the collaboration will provide proprietary genetic resource crosses and information to facilitate their utilization. Input on sources of germplasm and their attributes, potential new collaborators, and research initiatives will be solicited from project participants and the TSG. Improved website reporting of agronomic and abiotic stress resistance information will be done.
Obj 2: Approximately 50-100 breeding crosses will be evaluated in multiple environments and ~30 selected annually for development in Ames or collaborator nurseries. Exotic maize breeding crosses and new sources of exotic germplasm will be evaluated for important leaf and stalk rot diseases, reduced ear mold and mycotoxin production, abiotic stress tolerance, and host plant resistance to corn rootworm and above ground insects. Trait evaluations will be conducted in favorable selection environments for traits of interest. Breeding material will be evaluated for value added traits related to grain quality. Evaluation data will be stored in the GEM database. Research findings are shared via the public GEM website and scientific publications.
Obj 3: Germplasm will be developed primarily from 25% tropical/75% temperate breeding crosses. Breeding crosses will also be developed from tropical landrace accesses or modern tropical inbreds crossed with elite temperate germplasm resources, from GEM x GEM releases, and other models to maximize useful exotic germplasm contributions. Agronomic performance testing will be done in house and collaboratively.
A dual line development track will release 1) conventionally derived lines which have been tested and selected for agronomic and/or stress tolerance traits, and 2) lines developed purely for the purpose of capturing allelic diversity (AD) from exotic donor genomes that do not undergo selection for agronomic or other traits. The AD project lines are to represent all of the nearly 300 landraces, with an average of 25% of their genome derived from exotic introgressions and 75% from a recurrent, US-adapted parent.
Following release, lines will be genotyped and molecular marker information provided to help identify useful genetics for disease and insect resistance genes. Two years post-release, conventionally derived lines will be deposited in the National Plant Germplasm System. Incorporation of the AD lines into the NPGS collection depends on their value, as determined by the research community. Research findings will guide criteria for their inclusion; many will be incorporated over time.
Progress Report
Related to Objectives 1 and 3: Seven new Germplasm Enhancement of Maize (GEM) lines were released and distributed to ~30 GEM cooperators for the 2019 planting season. All lines were tested for adventitious presence (AP) of genetically engineered (GE) traits before distribution. Data associated with newly released line phenotypes, disease reactions, and yield trial evaluations were shared with collaborators and added to the GEM website.
Related to Objective 1: The 2019 spring season was cooler and wetter than normal resulting in field preparation and planting operation delays at nursery and yield trial sites. Program plans were changed several times to adjust to field conditions. Isolated crossing block nurseries planned for Ames, Iowa, are critical for generating hybrids used to evaluate segregating lines. Weather delayed planting beyond the optimal time to insure successful production of high-quality seed of adequate quantities. The isolation program was canceled for the summer season and plans shifted to producing the material at a winter site at a higher cost. Seed increase nurseries involving the allelic diversity project were also canceled for the year. These activities will be shifted to the summer 2020 program. Yield trial planting at one site was delayed until early June.
Approximately 16,700 Ames program yield trial plots were planted in 2019 at 16 locations with the combined effort of ARS researchers in Ames, Iowa, and Raleigh, North Carolina, and eleven private cooperators across the Midwestern United States (U.S.). This facilitates evaluation of GEM hybrids in a wider geographic region with more effective resource utilization. Summarized 2018 yield trial data was shared with collaborators and made available on the GEM website. One hundred ninety hybrids out of 2,400 GEM entries exceeded the mean yield of the check hybrids in Midwest trials in 2018. Of the 190 hybrids that exceeded the mean, 105 were from first year trials, and 85 from second year trials.
At the request of the GEM Technical Steering Group (TSG) the top 48 released GEM lines were identified by the Ames, Iowa, and Raleigh, North Carolina ARS programs in 2017 and seed distributed to each of the five private industry members of the TSG. The lines were crossed to each company's elite, proprietary tester lines in 2017 winter nursery sites. The resulting hybrids were tested within each company's system in 2017 and again in 2018. Data from the 2018 trials was returned to ARS researchers at Ames, Iowa, and analyzed for general combining ability (GCA) and specific combining ability (SCA) to evaluate the top GEM lines' competitive yield trial performance and potential breeding value. This is the first time that lines released from the GEM program have been evaluated for yield potential with current elite commercial germplasm across a wide range of environments and across years. The data will be shared with collaborators and stakeholder later this year. Knowledge will be shared on the GEM website.
More than 200 GEM pedigrees are being evaluated for Northern Leaf Blight (NLB), Southern Leaf Blight (SLB), Gray Leaf Spot, Goss’s Wilt, Head Smut, Tar Spot, Fusarium ear rot, and aflatoxin resistance with support from U.S. private cooperators in California, Iowa, Illinois, Michigan, and Nebraska; and from ARS scientists in Iowa, Missouri, Mississippi, and North Carolina. International cooperators conducted trials for globally important disease or insect pests in Africa, China, India, and Egypt. International diseases of concern include Maize Lethal Necrosis (MLN), Maize Rough Dwarf Virus (MRDV), Downy Mildew, Southern Rust, Late Wilt (Cephalosporium maydis), Heat Smut, Tar Spot, Pythium and Gibberella stalk rot, and NLB. Summarized disease evaluations from summer 2018 were shared with collaborators and added to the GEM website.
Related to Objective 2: Evaluation of breeding crosses is an important objective to determine adaptability and prioritization of exotic material for development. In 2019, 100 new breeding crosses (25% tropical) were planted for evaluation using the in-kind support of three cooperators, and by ARS researchers in Ames, Iowa. An additional 115 entry set (50% tropical) of breeding crosses were planted by ARS researchers in Raleigh, North Carolina, and one cooperator, for phenotypic evaluations. A final set of 212 breeding crosses produced in winter nursery was planted at Ames, Iowa, for evaluation. The 190 breeding crosses (50% tropical) and over 240 more (25% tropical) breeding crosses generated in 2018 provide critical characterization of tropical land-races and inbred lines to identify the best options for our temperate breeding programs.
Progenies of several breeding crosses distributed to GEM cooperators in previous seasons were returned for 2019 planting. Ten populations were advanced to the S1 (selfed once) generation with over 150 ears returned for each. Another cooperator advanced four breeding crosses through their company’s breeding system. The lines generated were top crossed to their own proprietary elite germplasm and yield tested in their system. Data from these trials were provided to the GEM Program and selected top performing lines were returned for advancement to GEM Program second year yield trials.
Summarized phenotypic observations of breeding crosses evaluated in summer of 2018 were shared among collaborators, and superior candidates identified for continued development. Twenty-four of these breeding crosses were included in GEM nursery sets at Ames, Iowa. Fifteen breeding crosses were distributed to nine GEM cooperators for planting in 2019 as part of their in-kind support. The populations sent to seven cooperators will be self-pollinated and a sample of each selected ear will be returned to the GEM program for 2020 nurseries. The remaining two cooperators will self-pollinate the populations and top cross selected ears to a proprietary elite tester from their program. The top-crosses will be yield tested in 2021. Lines selected based on yield trial results will be returned to the GEM program in late 2021.
Tropical land races and inbred lines require the use of a photoperiod control (shade) structure to reduce day length to 12 hours or less, necessary to induce flowering in Ames, Iowa. Unseasonably cool, wet weather during the planting season canceled 2019 shade structure use resulting in a shift in program focus to temperate zone-converted tropical germplasm. Nine converted tropical populations suggested by the chair of the GEM TSG and donated to the germplasm bank by the seed industry will be crossed to temperate lines in 2019. The converted tropical populations flower in the corn belt at a mid-season relative maturity and provide options for collaborators interested in earlier maturity breeding crosses.
Related to Objective 3: Four GEM lines released in 2017 were deposited in the National Plant Germplasm System (NPGS). Thirty of the allelic diversity programs double haploid BGEM lines (jointly released by Iowa State University (ISU) and ARS) were also deposited in the NPGS. Over 60 candidate lines for BGEM release were planted in the nursery for seed increase and final phenotypic evaluation. A summary of the lines selected for release will be communicated to collaborators and announced on the GEM website later this year.
Accomplishments
1. Resistance is needed to tar spot. Tar spot disease complex causes substantial yield loss to areas of southern Mexico and tropical areas of Latin America. The complex is caused by Phyllachora maydis Maubl, Mongraphella maydis Muller & Samuels, and Coniothyruim phyllachorae Manbl. Occurrence of Phyllachora maydis Maubl was first identified in the United States in leaf tissue collected at northern Illinois and central Indiana sites, and confirmed by the Purdue Plant and Pest Diagnostic Lab in 2015. The potential yield impact of the disease in the U.S. is not yet known. The ARS Germplasm Enhancement of Maize (GEM) Project in Ames, Iowa, is collaborating with plant pathologists at the University of Illinois, Michigan State University, Bayer Crop Science, Trimble Genetics, and CIMMYT (International Center for Maize and Wheat Improvement, Mexico) and supplied more than 200 GEM lines and BGEM lines (jointly released doubled haploid lines by Iowa State University and ARS) for tar spot resistance evaluation. Disease evaluation data will be shared on the GEM website. Any lines identified as resistant will be incorporated into breeding populations specifically targeting the disease, necessary to provide resistant germplasm for threats to U.S. corn production.
2. Resistance is needed to maize lethal necrosis (MLN). Maize lethal necrosis can result in corn yield losses of up to 90% in sub-Saharan Africa. The disease was first identified in Kenya in 2011 and has since spread to Rwanda, and the Democratic Republic of Congo. MLN was found to result from coinfection of maize with Maize chlorotic mottle virus (MCMV) and Sugarcane mosaic virus (SCMV). The disease has not been observed outside of Africa, but potential movement outside of the region is a concern. The ARS Germplasm Enhancement of Maize (GEM) Project in Ames, Iowa, is collaborating with CIMMYT (International Center for Maize and Wheat Improvement, Mexico) to screen over 200 GEM lines and BGEM lines (BEMS are doubled haploid lines jointly released by Iowa State University and ARS) for resistance to MCMV and SCMV. Two GEM lines derived from a Cuban accession have found to have resistance. Knowledge gained will be shared on the GEM website. The resistant lines are available for distribution and will be incorporated into breeding populations specifically targeting this disease to protect against yield loss.
