Location: Plant Introduction Research
2018 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
A total of 15,672 yield trial plots were planted in 2018 at 17 locations with the combined effort of the Germplasm Enhancement of Maize (GEM) Project in Ames, Iowa, and twelve 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.
Evaluation of breeding crosses is an important objective to determine adaptability and prioritization of exotic material for development. In 2018, 100 new breeding crosses were planted for evaluation using the in kind support of two cooperators, and also by ARS' Ames, Iowa program. A sub-set of the breeding crosses were planted by the ARS Plant Science Research Unit in Raleigh, North Carolina, for phenotypic notes. An additional 120 breeding crosses produced in winter nursery were planted at Ames for evaluation. In addition, more than 200 GEM pedigrees are being evaluated for Northern Leaf Blight (NLB), Southern Leaf Blight (SLB), Gray Leaf Spot, Goss’s Wilt, Bacterial Leaf Streak, Fusarium ear rot, and aflatoxin resistance with support by U.S. private cooperators in California, Iowa, Illinois, and Nebraska; and 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, Pythium and Gibberella stalk rot, and NLB.
Progeny of several breeding crosses distributed to GEM cooperators in previous seasons were returned for 2018 planting. Six populations were advanced to the S1 generation with over 150 ears returned for each. Another cooperator advanced four breeding crosses through their company’s doubled haploid (DH) 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.
Sixteen breeding crosses were distributed to nine GEM cooperators for planting in 2018 as part of their in kind support. The populations set to 7 cooperators will be self-pollinated and a sample of each selected ear will be returned after harvest to be worked in the GEM program. 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 2019. Lines selected based on yield trial results will be returned to the GEM Program in late 2019.
The objective of the Allelic Diversity (AD) project is to develop and release adapted exotic germplasm representing ~300 races of maize using traditional selfing and doubled haploid (DH) technology. New BC1F1 families are being crossed to a haploid inducer to create new DH's and the first selfing also conducted for these in 2018. The DH lines for future distribution are being increased by self-pollination of 454 rows representing approximately 60 races.
Accomplishments
1. Evaluation of top Germplasm Enhancement of Maize (GEM) released lines. Performance of GEM released lines across a wide range of commercial elite testers would provide information on the value of the lines in breeding programs. The GEM Programs at Ames and Raleigh identified the top 48 lines and distributed seed to each of the five private industry members of the Technical Steering Group (TSG). The 48 lines were crossed to elite testers from each company and the resulting hybrids were tested within each companies system in 2017. The participants also agreed to test these hybrids again in 2018. Data from the 2017 trials was returned to ARS researchers at Ames, Iowa, and run through a general combining ability (GCA) and specific combining ability (SCA) analysis which provides a competitive evaluation of the yield trial performance and potential breeding value of the top GEM lines. 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. The data will be helpful to all GEM stakeholders.
2. Resistance to Bacterial Leaf Streak. Bacterial Leaf Streak was first confirmed in Nebraska corn fields in 2016 and in Brazilian maize production fields in 2018. Since then, significant yield losses have been confirmed in various locations. The full potential yield impact of the disease in the U.S. is not yet understood and little is known regarding sources of genetic resistance. Collaboration with plant pathologists at the University of Nebraska to screen 100 GEM released lines for disease resistance identified multiple lines with resistance, which has not been found previously. The test is being repeated for confirmation in 2018, and lines can be incorporated into breeding programs specifically for this disease.
