Michael Blanco

Resistant-Starch Formation in High-Amylose Maize Starch during Kernel Development

The objective of this study was to understand the resistant-starch (RS) formation during kernel development of a high-amylose maize, GEMS-0067 line. The RS content of the starch, determined using AOAC method 991.43 for total dietary fiber, increased with kernel maturation and increase in the amylose/intermediate component (IC) content of the starch. Gelatinization of the native starches showed a major thermal transition with peak temperature at 76.6-81.0 degrees C. An additional peak ( approximately 97.1 degrees C) first appeared 20 days after pollination and then developed into a significant peak on later dates. After removal of lipids from the starch, this peak disappeared, but the conclusion gelatinization temperature remained the same. The proportion of the enthalpy change of the thermal transition above 95 degrees C, calculated from the thermogram of the defatted starch, increased with kernel maturation and was significantly correlated with the RS content of the starch (r = 0.98). These results showed that the increase in crystallites of amylose/IC long-chain double helices in the starch resulted in the increase in the RS content of the starch during kernel development.

Characterization of normal and waxy corn starch for bioethanol production.

Objectives of this study were to compare ethanol production between normal and waxy corn using a cold fermentation process and to understand effects of starch structures and properties on ethanol production. Ethanol yields positively correlated (p < 0.01) with starch contents of kernels of the normal and waxy corn. The average starch-ethanol conversion efficiency of waxy corn (93.0%) was substantially greater than that of normal corn (88.2%). Waxy corn starch consisted of very little amylose and mostly amylopectin that had a shorter average branch chain length than normal corn amylopectin. Regression analyses showed that average amylopectin branch chain lengths and percentage of long branch chains (DP > 37) of waxy corn starch negatively correlated with the starch hydrolysis rate and the ethanol yield. These results indicated that starch structures and properties of the normal and waxy corn had significant effects on the ethanol yield using a cold fermentation process.

Characterization of Corn Grains for Dry-Grind Ethanol Production

The objectives of this study were to understand how the composition of corn kernels and starch structure affected the enzyme hydrolysis of starch in dry-grind corn and the ethanol yield from yeast fermentation. Four selected corn inbred lines were used in this study. Starch in uncooked dry-grind corn samples showed greater enzyme digestibility than did the uncooked starch isolated from the same source by wet-milling process. The greater digestibility of starch in uncooked dry-grind corn correlated with a physical damage of starch granules. In contrast, starch in cooked dry-grind corn samples displayed less enzyme digestibility than did the cooked isolated starch. The difference could be attributed to interference caused by non-starch components in the dry-grind corn. The entrapment of starch in protein matrix and the formation of amylose-lipid helical complexes and/or retrograded starch may decrease the enzyme digestibility of starch in cooked dry-grind corn. Lab-scale ethanol production showed that ethanol yield after 72 h fermentation of the four corn inbred lines ranged between 34.3 and 38.0 g ethanol/100 g dry-grind corn. The conversion efficiency at 72 h of fermentation ranged between 86.8 % and 90.3 % of the theoretical ethanol yield. The highest ethanol yield was found in the corn line containing the largest starch content and the smallest amounts of lipid and protein.

Evaluation of Corn Germplasm Lines for Multiple Ear-Colonizing Insect and Disease Resistance

ABSTRACT Ear-colonizing insects and diseases that reduce yield and impose health threats by mycotoxin contaminations in the grain, are critical impediments for corn (Zea mays L.) production in the southern United States. Ten germplasm lines from the Germplasm Enhancement of Maize (GEM) Program in Ames, IA, and Raleigh, NC, and 10 lines (derived from GEM germplasm) from the Texas Agricultural Experiment Station in Lubbock, TX, were examined in 2007 and 2008 with local resistant and susceptible controls. Four types of insect damage and smut disease (Ustilago maydis) infection, as well as gene × environment (G × E) interaction, was assessed on corn ears under field conditions. Insect damage on corn ears was further separated as cob and kernel damage. Cob penetration rating was used to assess corn earworm [Helicoverpa zea (Boddie)] and fall armyworm [Spodoptera frugiperda (J.E. Smith)] feeding on corn cobs, whereas kernel damage was assessed using three parameters: 1) percentage of kernels discolored by stink bugs (i.e., brown stink bug [Euschistus servus (Say)], southern green stink bug [Nezara viridula (L.)], and green stink bug [Chinavia (Acrosternum) hilare (Say)]; 2) percentage of maize weevil (Sitophilus zeamais Motschulsky)—damaged kernels; and 3) percentage of kernels damaged by sap beetle (Carpophilus spp.), “chocolate milkworm” (Moodna spp.), and pink scavenger caterpillar [Pyroderces (Anatrachyntis) rileyi (Walsingham)]. The smut infection rates on ears, tassels, and nodes also were assessed. Ear protection traits (i.e., husk tightness and extension) in relation to insect damage and smut infection also were examined. Significant differences in insect damage, smut infection, and husk protection traits were detected among the germplasm lines. Three of the 20 germplasm lines were identified as being multiple insect and smut resistant. Of the three lines, entries 5 and 7 were derived from DKXL370, which was developed using corn germplasm from Brazil, whereas entry 14 was derived from CUBA117.

Gibberellins Promote Brassinosteroids Action and Both Increase Heterosis for Plant Height in Maize (Zea mays L.)

Brassinosteroids (BRs) and Gibberellins (GAs) are two classes of plant hormones affecting plant height (PHT). Thus, manipulation of BR and GA levels or signaling enables optimization of crop grain and biomass yields. We established backcross (BC) families, selected for increased PHT, in two elite maize inbred backgrounds. Various exotic accessions used in the germplasm enhancement in maize project served as donors. BC1-derived doubled haploid lines in the same two elite maize inbred backgrounds established without selection for plant height were included for comparison. We conducted genome-wide association studies to explore the genetic control of PHT by BR and GA. In addition, we used BR and GA inhibitors to compare the relationship between PHT, BR, and GA in inbred lines and heterozygotes from a physiological and biological perspective. A total of 73 genomic loci were discovered to be associated with PHT, with seven co-localized with GA, and two co-localized with BR candidate genes. PHT determined in field trials was significantly correlated with seedling stage BR and GA inhibitor responses. However, this observation was only true for maize heterozygotes, not for inbred lines. Path analysis results suggest that heterozygosity increases GA levels, which in turn promote BR levels. Thus, at least part of heterosis for PHT in maize can be explained by increased GA and BR levels, and seedling stage hormone inhibitor response is promising to predict heterosis for PHT.

Extensive genetic diversity and low linkage disequilibrium within the COMT locus in maize exotic populations.

The caffeic acid 3-O-methytransferase (COMT) gene is a prime candidate for cell wall digestibility improvement based on the characterization of brown midrib-3 mutants. We compared the genetic diversity and linkage disequilibrium at this locus between exotic populations sampled within the Germplasm Enhancement of Maize (GEM) project and 70 inbred lines. In total, we investigated 55 exotic COMT alleles and discovered more than 400 polymorphisms in a 2.2 kb region with pairwise nucleotide diversity (π) up to 0.017, much higher than reported π values of various genes in inbred lines. The ratio of non-synonymous to synonymous SNPs was 3:1 in exotic populations, and significantly higher than the 1:1 ratio for inbred lines. Selection tests detected selection signature in this gene in both pools, but with different evolution patterns. The linkage disequilibrium decay in exotic populations was at least four times more rapid than for inbred lines with r²>0.1 persisting only up to 100 bp. In conclusion, the alleles sampled in the GEM Project offer a valuable genetic resource to broaden genetic variation for the COMT gene, and likely other genes, in inbred background. Moreover, the low linkage disequilibrium makes this material suitable for high resolution association analyses.

Dosage effects of Waxy gene on the structures and properties of corn starch

The objective of this study was to understand dosage effects of the Waxy gene on the structures of amylose and amylopectin and on the properties of corn starch. Reciprocal crossing of isogenic normal and waxy corn lines was conducted to develop hybrids with different dosages (0, 1, 2, 3) of Waxy gene in the endosperm. The amylose content of starch and proportions of branch chains of DP 17-30 and extra-long branch chains (DP>100) of amylopectin were positively correlated with the Waxy-gene dosage. Proportions of short (DP<17) and long branch-chains (DP 30-80), however, were negatively correlated with the Waxy-gene dosage. The gelatinization conclusion-temperature and temperature-range of the starch were negatively correlated with the Waxy-gene dosage, indicating that amylose facilitated dissociation of the surrounding crystalline regions. These results helped us understand the function of granule-bound starch synthase I in the biosynthesis of amylose and amylopectin and impacts of Waxy-gene dosages on the properties of corn starch.

Evaluation of fall armyworm resistance in maize germplasm lines using visual leaf injury rating and predator survey.

After examining ear‐colonizing pest resistance, 20 maize lines from the USDA‐ARS Germplasm Enhancement of Maize (GEM) Program were evaluated for whorl‐feeding fall armyworm (FAW) (Spodoptera frugiperda) resistance using 4 maize inbred lines as the resistant and susceptible controls. Both FAW injury ratings at 7‐ and 14‐d after infestation, and predator abundance and diversity at whorl stage (V6–V8) were recorded in 2009 and 2010. The survey of the diversity and abundance of predators in each experimental plot were conducted 7 d after the FAW infestation. Of the 20 germplasm lines examined, 3 of them (i.e., entries 9, 15, and 19 that were derived from tropical maize germplasm lines were originated from Uruguay, Cuba, and Thailand, respectively) were identified as the best FAW‐resistant germplasm lines using the leaf injury ratings and predator survey data. In addition, the abundance and diversity of the predators were greater in 2010 than in 2009, which might have caused the low level of the FAW injury ratings on all lines examined in 2010. The 2‐year data showed that the FAW injury ratings were negatively correlated to the predator abundance and diversity, which is also influence by genotype × environment interactions. The findings suggested that tropical germplasm is an important source of native resistance to the FAW and the corn earworm. At the same time, the maize genotype × environment interaction (e.g., predator attractiveness, and varying weather conditions) should be included in the multiple‐year evaluations of insect and disease resistance of maize germplasm lines under field conditions.

Genome-wide association studies of doubled haploid exotic introgression lines for root system architecture traits in maize (Zea mays L.)

Root system architecture (RSA) is becoming recognized as important for water and nutrient acquisition in plants. This study focuses on finding single nucleotide polymorphisms (SNPs) associated with seedling RSA traits from 300 doubled haploid (DH) lines derived from crosses between Germplasm Enhancement of Maize (GEM) accessions and inbred lines PHB47 and PHZ51. These DH lines were genotyped using 62,077 SNP markers, while root and shoot phenotype data were collected from 14-day old seedlings. Genome-wide association studies (GWAS) were conducted using three models to offset false positives/negatives. Multiple SNPs associated with seedling root traits were detected, some of which were within or linked to gene models that showed expression in seedling roots. Significant trait associations involving the SNP S5_152926936 on Chromosome 5 were detected in all three models, particularly the trait network area. The SNP is within the gene model GRMZM2G021110, which is expressed in roots at seedling stage. SNPs that were significantly associated with seedling root traits, and closely linked to gene models that encode proteins associated with root development were also detected. This study shows that the GEM-DH panel may be a source of allelic diversity for genes controlling seedling root development.

Association Mapping of Flowering and Height Traits in Germplasm Enhancement of Maize Doubled Haploid (GEM-DH) Lines

Genome‐wide association mapping in exotic derived double haploid maize lines. Genomic areas collocate with previously identified QTLs and candidate genes for flowering and height. Novel regions identified allow for future research of adapting exotic maize to the central‐U.S. Corn‐Belt.