Location: Plant Introduction Research2013 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:
This is the final report of the project. A new five year Plan was prepared and certified on April 3, 2013. Eight new GEM releases were distributed to cooperators for the 2013 planting season and 68 total releases during the period 2008-2012. Over the project's 20 year history 258 lines have been released by the GEM Project network of which 190 are publicly available through the Genetic Resources Information Network (GRIN). Approximately 10,700 yield trial plots were planted in 2013 at 46 trial locations with the combined effort of the GEM Project and 11 private cooperators. During the past five years approximately 78,000 yield trial plots (approximately 14,000 entries) were coordinated through Ames. Yield trials were planted at four locations for over 400 entries (top crosses) derived from CUBA164 X B73) x B73, and CUBA164 x PHB47) x PHB47. Objectives of this project include mapping the genes involved in adaptation to high plant density. The evaluation of breeding crosses is an important objective to determine adaptability and prioritization of exotic material for development. One hundred breeding crosses were planted in 2013, and approximately 100 per year for the past five years through in kind support from two cooperators, AgReliant and G and S Crop Services. A shade house was constructed in 2013 to reduce photoperiod response in tropical germplasm in order for crosses to be made to temperate germplasm. Approximately 50 tropical x temperate crosses will be made in 2013 using the shade house. During the past five years 278 tropical x temperate crosses were made using the shade house. 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. Approximately 175 rows were planted for traditional self pollination of segregating AD families, and 1,158 rows for seed increase of DH lines. The DH lines represent 252 inbreds which are being increased for public distribution to the maize research community. In addition, approximately 300 rows of nursery were planted to support development of a new haploid inducer inbred with better adaptation to the Midwest than the inducer line currently being used. A random mating nursery was planted in Ames to study if exotic alleles are less likely to survive the DH process if the original BC1 populations (versus random mated BC1's) are used for haploid induction. The study includes 22 BC1-sib 1 families. The objective of this project is to continue the second cycle of sib mating to make the BC1-sib2 that would be used for haploid induction the next season.
1. New sources of doubled haploid (DH) inbreds. 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. An important source of exotic germplasm are inbred lines that are uniform, consistently breed true by self pollination, and have a fixed set of chromosomes contributed equally by each parent. Inbred lines are "diploid"(carry two sets of the basic chromosome number) and each parent contributes half the chromosome number or "haploid" set. ARS scientists in Ames utilize doubled haploid (DH) technology which is a genetic method to create haploids followed by doubling the chromosomes to develop completely homozygous, diploid inbreds. More than 15,000 self pollinations were made in 2013 to increase seed of 252 DH inbreds representative of 52 maize races which will be made available to the maize community. Utilization of DH technology accelerates the inbreeding process by reducing cycle time from the traditional 8 generations to 3 generations, and will provide unique adapted genetic resources to support agronomic improvement, gene discovery. Findings from use of this germplasm (which contains alleles introgressed from tropical germplasm) may contribute to increasing the diversity of commercial maize.
Henry, W.B., Windham, G.L., Rowe, D.E., Blanco, M.H., Murray, S.C., Williams, W.P. 2013. Diallel analysis of diverse maize germplasm lines for resistance to aflatoxin accumulation. Crop Science. 53:394-402.