2013 Annual Report
1a.Objectives (from AD-416):
Maize contains an incredible amount of genetic and phenotypic diversity considering its crop history – domestication from teosinte in Mexico, adaptation and spread of landraces across the Americas prior to the Columbian exchange, and intense selection for productivity and other agronomic traits during modern plant breeding. Allelic diversity in the genes underlying seed composition has changed dramatically as a result of artificial selection during domestication and breeding, leading to the modern hybrids of today. In order to identify genes underlying kernel composition and to continue to improve kernel traits in maize, we must realize the full range of variation for these traits in maize. Many studies have been conducted to investigate small numbers of composition traits in narrow samples of maize germplasm. Here we propose to conduct a very thorough analysis of grain composition and metabolites in a set of hybrids representing the range of domesticated maize. The formal objective of this project is to investigate the natural variability of composition traits and metabolic profiles in maize grain derived from diverse inbred lines and landraces.
1b.Approach (from AD-416):
The parties propose to comprehensively analyze the kernel composition and metabolite profiles in two sets of B73 hybrids with: 26 NAM inbred parents (plus Mo17) and 20 landrace inbreds. The NAM (nested association mapping) parents are inbred lines that were chosen to maximally capture genetic diversity and thus represent the scope of inbred diversity from around the world. The landrace inbreds are a set of partial inbreds (5-6 selfing generations) that were selfed directly from landrace accessions by a scientist at the University of Wisconsin. The two sets of parental lines for these hybrids have been the subject of intense phenotypic, genetic, and genomic investigation by the Maize Diversity Project, where 55 million single nucleotide polymorphisms (SNPs) were identified across this germplasm and a genome-wide domestication study identified approximately 1000 genes that experienced artificial selection during domestication and/or breeding. Replicated trials (Columbia, MO and Ithaca, NY, 3 replicates each) were grown in 2012, and plants were self-pollinated to produce seed for composition studies. Seed samples will be analyzed for kernel composition traits (e.g. proximates, amino acids, fatty acids, and selected vitamins) and submitted for metabolite profiling via GC/MS (e.g. 300 metabolites including free amino acids, sugars and organic acids). We will use established statistical methods to determine the effect of the genotype, environment, and genotype x environment on levels and interrelationships of these traits.
The objectives of this research directly relate to Objective 2 of the parent project: Characterize the genetic basis of important agronomic traits (heterosis, drought tolerance, yield components, DIMBOA synthesis, and kernel composition) in maize. Sub-objective 2.4: Determine the genetic basis of kernel composition in maize x teosinte introgression libraries, and compare the QTL and effects to those observed in maize. The NFCA provides data on which inbred lines contain useful composition and metabolite traits.
ARS scientists conducted trials with three replicates each at Ithaca, NY and Columbia, MO in 2012. At the Ithaca location, the plants were self-pollinated to produce grain for lab analyses, and the following data were collected: maturity, plant/ear height, kernel row number, ear length/width, cob length/width, and seed weight. Seed was sent to Monsanto for composition and metabolite analysis. At the Columbia location, plants were self-pollinated to produce grain for lab analyses, and the same data were collected as in Ithaca.
The Columbia trial is being repeated in 2013. The same data will be collected, and seed will be sent to Monsanto for analysis.