Location: Plant Introduction Research2011 Annual Report
1a. Objectives (from AD-416)
The long-term objectives of this project are to identify and incorporate useful maize genetic diversity to support sustainable productivity of the most important crop in the United States, as measured by acreage planted, farm gate value, product value and strategic importance. To accomplish this, we will: 1) manage and coordinate a multi-site, cooperative program of maize germplasm evaluation, genetic enhancement, inbred line development, and information sharing focused on broadening the genetic base for U. S. maize; 2) evaluate maize germplasm with a broad spectrum of non-U.S. and mixed U.S./non-U.S. pedigrees for adaptation, yield, resistance to biotic and abiotic stresses, and key value-added traits; 3) breed and release genetically-enhanced populations and inbred lines, derived from non-U.S. and/or mixed U.S./non-U.S. germplasm sources, that are commercially-competitive and/or which contain key traditional or novel traits; and 4) develop innovative means of managing and transferring evaluation and breeding information to multiple project cooperators and germplasm users.
1b. Approach (from AD-416)
Extensive collaboration efforts on the part of 60 current cooperators from the private, public and international sectors are required to broaden the germplasm base in effective ways that provide germplasm of use for food, feed, fuel, and industrial applications by producers and end-users. The Coordinator serves as the liaison for collaborators and the Technical Steering Group (TSG), selects germplasm, facilitates germplasm acquisition and stakeholder interactions, arranges for in-kind-support, information sharing, and technology transfer. The Ames location will develop germplasm derived from 50% and 25% exotic breeding crosses developed by crossing tropical and temperate racial accessions with adapted, elite proprietary Corn Belt lines. Approximately 1,500 -1,600 S2 top crosses will be made and evaluated annually in yield trials, disease nurseries, and for value-added traits such as ethanol, protein, oil, and starch. Germplasm will be further evaluated by a network of cooperators with expertise, facilities, and favorable selection environments for the traits of interest. Important traits include mycotoxin resistance, abiotic stress tolerance, and insect resistance. Germplasm lines will be released to cooperators and selected lines registered and publicly released. Released lines will be maintained by the National Plant Germplasm System's maize curator. An effort will be made to develop lines derived from approximately 250 races of maize to broadly represent the allelic diversity of the maize races. Initial crosses of racial accessions with expired PVP lines or other public lines are made in winter nurseries, and one backcross to the adapted line (BC1). The resulting BC1 generation will be used for selecting lines in Midwest nurseries in order to release a unique set of (F5 generation) adapted, racial derivative lines for research and discovery applications. Technologies and methodologies can be utilized such as SNP or SSR markers for genomic profiling and association analysis that offer potential to translate genomic knowledge to germplasm enhancement and utilization applications. Genotypes will be screened in selected environments to maximize selection for priority agronomic, biotic and abiotic stress, reduced mycotoxin, and value-added traits.
3. Progress Report
Progress was made on all four objectives and sub-objectives. An important objective is the development of adapted exotic inbred lines representing 300 races of maize using double haploid and traditional plant breeding methods. Through the combined support of two private Germplasm Enhancement of Maize (GEM) cooperators, 400 rows of doubled haploid (DH) families developed in Ames, IA, were planted in two tropical winter nurseries to increase seed for the 2011 nursery. Approximately 300 DH families were returned and planted for seed increase. In addition, 38 new haploid populations representing 28 races (1,710 plants) were treated at the 3-leaf stage with a chromosome doubling agent, colchicine, grown by the Iowa State University (ISU) Doubled Haploid Facility for two more weeks, and transplanted in the nursery. To enhance our ability to detect haploid plants we initiated development of a new haploid inducer line using a yellow dominant mutant received from the Maize Genetics Stock Center. (The current genetic marker is not detectable in many exotic backgrounds due to color inhibitor genes). For the traditional breeding program, approximately 504 nursery rows were devoted to the Allelic Diversity (AD) project which comprised 110 races from 13 countries. Presently, 187 races from 227 accessions are at the first backcross (BC1) stage, and approximately 10 populations are at the F5 or later inbreeding generation. Approximately 16,500 yield trial plots were planted at 53 trial locations with the combined efforts of the GEM Project and 12 private cooperators. Efforts continue to create an exotic mapping population using CUBA164 (PI 489361) as the elite exotic source identified in the GEM Project. Approximately 230 S2 families from (CUBA164 x B73) x B73, and 230 S2 families from (CUBA164 x PHB47) x PHB47 were planted in the LH287 iso to make test crosses. Research continued utilizing the shade structure to make new tropical x temperate crosses in Ames. In addition to 40 tropical maize sources, two teosinte subspecies (parviglumis and mexicana) were planted to determine if early flowering can be induced under shade structures. Seed was increased of four host differentials for Southern Rust known to have the Rpp9 gene. This is a cooperative effort with the Agricultural Research Service (ARS) Maize Curator, Pioneer Hi-Bred, and ARS researchers at Raleigh, NC and various universities. Two new cooperators joined the GEM Project: Semillas Fito SA, a private cooperator from Spain, and Genetic Resources, Inc, a private U.S. cooperator. The new cooperators will expand our access to exotic European germplasm, provide virus disease data for Spain, and enhance our ability to evaluate normal and high amylose starch germplasm in the U.S. Other research collaborations in progress with the public and private sectors include germplasm evaluation and/or development with nine universities, two private companies, and five USDA-ARS research units for mycotoxin, abiotic stress, southern leaf blight, grey leafspot, corn root worm, multiple insect resistance, and starch properties for ethanol potential, digestibility, and resistant starch for human health applications.
1. New sources of germplasm. The corn germplasm base in the U.S. is extremely narrow, and lack of genetic diversity can lead to genetic vulnerability to pathogens and insects, and limit genetic gain from selection. The Germplasm Enhancement of Maize (GEM) Project utilizes traditional breeding and double haploid (DH) induction technology to expedite development of inbreds from exotic races. From the traditional breeding program Agricultural Research Service researchers in Ames, IA, released 6 lines for 2011. Two of the lines had protein levels above 13% (normal is 9-10%), and were derived from crosses involving two GEM inbreds (second cycle). From the DH research, 379 finished inbreds representing 74 exotic races were increased in the nursery and will be valuable sources of diversity which can potentially broaden the germplasm base. Disease screening efforts by the network identified materials with exceptional resistance to Fusarium ear mold. Utilization of adapted germplasm by university researchers is designed to provide new knowledge and technology related to exotic germplasm. Use of DH technology with useful exotic germplasm reduces breeding cycle time from the traditional 8 generations of inbreeding to 3 generations. Shortening breeding cycle time provides opportunity to increase the rate of genetic gain per year. An increased rate of genetic gain enables more rapid deployment of genes/traits/varieties to address production issues and food security.
Jiang, H., Lio, J., Blanco, M.H., Campbell, M., Jane, J. 2010. Resistant-starch Formation in High-amylose Maize Starch During Kernel Development. Journal of Agriculture and Food Chemistry. 58:8043-8047.