Browsing by Subject "aflatoxin"
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Item Breeding Maize for Drought Tolerance: Diversity Characterization and Linkage Disequilibrium of Maize Paralogs ZmLOX4 and ZmLOX5(2012-07-16) De La Fuente, GeraldMaize production is limited agronomically by the availability of water and nutrients during the growing season. Of these two limiting factors, water availability is predicted to increase in importance as climate change and the growing urban landscape continue to stress limited supplies of freshwater. Historically, efforts to breed maize for water-limited environments have been extensive; especially in the areas of root architecture and flowering physiology. As progress has been made and new traits have been discovered and selected for, the different responses to drought stress at specific developmental stages of the maize plant have been selected as a whole when drought tolerance is evaluated. Herein we attempt to define the characteristics of the maize drought response during different developmental stages of the maize plant that can be altered through plant breeding. Towards breeding for drought tolerance, 400 inbred lines from a diversity panel were amplified and sequenced at the ZmLOX4 and ZmLOX5 loci in an effort to characterize their linkage disequilibrium and genetic diversity. Understanding these characteristics is essential for an association mapping study that accompanies this project, searching for novel and natural allelic diversity to improve drought tolerance and aflatoxin resistance in maize. This study is among the first to investigate genetic diversity at important gene paralogs ZmLOX4 and ZmLOX5 believed to be highly conserved among all Eukaryotes. We show very little genetic diversity and very low linkage disequilibrium in these genes, but also identified one natural variant line with knocked out ZmLOX5, a variant line missing ZmLOX5, and five line variants with a duplication of ZmLOX5. Tajima's D test suggests that both ZmLOX4 and ZmLOX5 have both been under neutral selection. Further investigation of haplotype data revealed that ZmLOX12, a member of the ZmLOX family, showed strong LD that extends much further than expected in maize. Linkage disequilibrium patterns at these loci of interest are crucial to quantify for future candidate gene association mapping studies. Knockout and copy number variants of ZmLOX5, while not a surprising find, are under further investigation for crop improvement.Item Calcium Montmorillonite for the Mitigation of Aflatoxicosis and Gastrointestinal Inflammation(2014-08-06) Zychowski, Katherine EClays have been used for centuries as ?ancient medicine? for their therapeutic benefits. One particular clay, calcium montmorillonite, has historically been used as an anti-caking agent in animal feeds, but has also demonstrated the ability to bind toxins and alleviate infectious diarrhea. The full breadth of therapeutic applications and molecular mechanisms of montmorillonite is still unknown. Therefore, the purpose of this research was to explore novel therapeutic applications for NovaSil (NS), a calcium montmorillonite clay to reduce the risk of aflatoxicosis in farm-raised fish and alleviate gastrointestinal inflammation and dysbiosis in a mouse model of Crohn?s disease (CD). Aflatoxin B_(1) (AFB_(1)) is a fungal mycotoxin that commonly contaminates corn and peanut crops. It is produced by the fungi Aspergillus flavus and A. parasiticus during times of drought or due to improper post-harvest storage. Aflatoxin B_(1) is known to cause hepatocellular carcinoma, immunosuppression and growth stunting in several species. Recently, incorporation of plant-based alternatives into feed for farm-raised fish has become a trend, thereby increasing the risk for mycotoxin contamination. Inexpensive strategies to reduce AFB_(1) exposure are needed. Calcium montmorillonite clay, which is both inexpensive and abundant, has a dioctahedral structure that is known to sequester AFB_(1) in its negatively-charged interlayer, thereby reducing systemic bioavailability. There is also some evidence to suggest that calcium montmorillonite clays may possess gastrointestinal anti-inflammatory properties. NovaSil was used as a strategy to reduce the effects of AFB_(1) in Nile tilapia (Oreochromis niloticus) and red drum (Scieanops ocellatus). Juvenile tilapia and red drum were dosed with AFB_(1) and NS over the course of 10 and 7 weeks, respectively. Additionally, proinflammatory cytokine-clay binding was characterized using isothermal analysis, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, a TNBS (2,4,6-Trinitrobenzenesulfonic acid)-colitis gastrointestinal mouse model was employed to study the anti-inflammatory properties of NS and its ability to protect the gut microbiome. Results suggest that NS can prevent aflatoxicosis in red drum at a 2% inclusion level over the course of 7 weeks. NovaSil also prevented some toxicity in Nile tilapia; however, these results were not significant. In vitro results also indicate that NS sorbs proinflammatory cytokines such as TNF? and IL-1? in its interlayers. Additionally, NS was found to reduce serum pro-inflammatory cytokine levels in TNBS-induced mice and reduce gut dysbiosis. These results could positively impact both human and animal populations with AFB_(1) exposure and/or chronic gastrointestinal inflammation.Item Characterization and Safety of Clays as Potential Dietary Supplements to Prevent Aflatoxicosis(2011-05-10) Marroquin-Cardona, Alicia 1979-Aflatoxins are toxic metabolites produced by Aspergillus flavus and A. parasiticus fungi. Aflatoxin B1 (AFB1) is the most toxic and is a potent carcinogen with antinutritional and immunosuppressive effects. Several natural outbreaks of poisoning have been reported in both animals and humans, with fatal consequences in some of the cases. Inclusion of clay minerals in the diet is a promising strategy to reduce the bioavailability of aflatoxins from contaminated foods. Several clay-based products are currently sold as ?mycotoxin binders? for addition in feeds, many of them lacking of detailed efficacy and safety data. Similarly, clays intended for human consumption in different countries also lack of safety studies, and for most of them the mineral composition is unknown. Earlier studies in our laboratory have shown that NovaSil clay (NS), a Ca-bentonite, is able to reduce the adverse effects associated with aflatoxin exposure in different animal species and recent human trials have confirmed its efficacy and safety. Most clays are derived from naturally-occurring deposits and batch-to-batch variations in composition, particle size, non-framework trace metal content and dioxin levels are expected. Therefore, objectives in this research were to determine the mineral composition, aflatoxin binding capacity and potential safety of ?mycotoxin binders? and edible clays for humans, and to investigate the mineral characteristics and safety of two potential aflatoxin adsorbents, a refined clay with more uniform particle size (UPSN) and a sodium bentonite (Na-BENT). Both clays have low dioxin/furans and heavy metals levels. According to mineralogical analysis, most of the ?binders? contained montmorillonite but the sorption capacities for AF varied. Most of the edible clays for humans contained kaolinite, mica and quartz, and they had low sorption capacities for aflatoxin. UPSN and Na-BENT had similar mineral characteristics and high sorption capacities for aflatoxin. After a 3-month rodent study using Sprague Dawley rats, no overall toxicity was observed for either clay. No changes were observed for most of the blood and serum biochemical parameters. Important findings included the increased serum Na, Ca, vitamin E and Na/K ratio and the reduction of serum K and Zn (in males) due to ingestion of the bentonites. Nonetheless, all parameters fell within the normal ranges reported for rats less than 6 months old and no trends of dose dependency were observed. We conclude that ingestion of low levels of bentonites does not present a health risk.Item Detecting Aflatoxicosis in Broilers in the Evaluation of Clay-based, Toxin-binding Feed Additives(2014-11-17) Fowler, Justin CaseThe objectives of this research were to evaluate common biological measures of aflatoxicosis in broilers (such as growth rate and relative organ weights) along with variables such as hepatic gene expression and aflatoxin residues in the liver, pursuant to identifying a more sensitive biological assay that will allow researchers to conduct three-week broiler trials at aflatoxin concentrations <1000 ppb, prior to significant changes in the growth rate or relative organ weights. This will help us both better understand how aflatoxicosis presents in broilers, as well as help us evaluate the efficacy of clay-based binders for their ability to ameliorate aflatoxicosis under experimental conditions. In the first study, a recently mined calcium bentonite clay (TX4) was evaluated against Novasil?. Both clays appeared able to sequester aflatoxin, and overall TX4 appeared capable of ameliorating aflatoxicosis comparable to Novasil?. In the second study, growth and relative organ weight data were compared with the gene expression of hepatic enzymes known to detoxify aflatoxin B1 in broilers that had consumed a wide range of aflatoxin concentrations. When gene expression data from liver samples were analyzed, the genotypic effect of aflatoxin on the CYP1A1 and CYP2H1 isoforms simply mirrored the phenotypic effects seen in the growth and relative organ weights, suggesting that this variable was not any more sensitive than the more traditional ones. The third study evaluated the TX4 clay when in diets containing <1000 ppb aflatoxin. Although weight gain was unaffected by aflatoxin at these lower levels (after three weeks on treatment diets, body weights between the 0 ppb treatment and the 700 ppb treatment only varied by 4%), there were negative effects on feed conversion and productivity index and there was an increase in the relative weights of the liver and kidney. The inclusion of TX4 to the treatment diets did not offer any amelioration from the main effects of aflatoxin. Finally, a study was conducted to evaluate the effects of TX4 clay when using residues of aflatoxin B1 in the liver as the primary variable of interest. Results after one week on treatment diets showed that TX4 was effective at reducing the accumulation of aflatoxin B1 residues in liver. However, after the first week, liver residue data were not any more sensitive in evaluating aflatoxin or clay effects when compared to the ?traditional? measures of growth performance and organ weights. Also, these results indicate that the clearance time required to remove aflatoxin residues from the liver is less than one week on a clean corn diet. Based on these evaluations, attempts to characterize a more sensitive, sentinel-type response to aflatoxin exposure in broilers were not any more successful at evaluating aflatoxicosis than was the common bioassay measures such as growth rate and relative organ weights. These studies (by contaminating corn with aflatoxigenic species of Aspergillus) were able to find significant main effects for aflatoxin at lower concentrations (?1000 ppb) than had been previously reported by the studies that included inoculated rice.Item Economic Analysis of Atoxigenic Mitigation Methods for Aflatoxin in Corn in Central Texas(2014-04-09) Sampson, Jessica SueAtoxigenics and crop insurance are available to producers to assist in preventing economic loss from aflatoxin contamination in corn. Atoxigenics are a newer technology available to farmers, and although professional opinion of this biotechnology encourages its use, an economic analysis has not been performed to determine if the atoxigenics are overall economically beneficial to the producer when combined with crop insurance. The objective of this paper is to perform an economic analysis on the decision to use available atoxigenic treatments on a corn crop, and evaluate the economic outcome at different crop insurance levels for corn producers in Central Texas. This paper will use a risk based partial budget simulation model combined with an aflatoxin contamination simulation model to complete a risk analysis on the decision to use atoxigenic mitigation methods. Field level data on aflatoxin contamination levels is from Bell County, Texas. A representative farm was simulated with and without atoxigenic treatments and each case was simulated across a range of crop insurance options available to corn producers in Bell County. A total of 50 scenarios were simulated and compared based on net revenue. Results show atoxigenics do provide a monetary benefit to producers. When the atoxigenic treatment was compared to no atoxigenic treatment, both with no insurance, the simulated average net revenue was higher by $8-$10 per acre for the treatment scenario. When crop insurance was simulated, with and without atoxigenic treatments, results indicated the current RMA insurance premiums were too high for treatment scenarios. The current RMA premiums did not account for the decreased risk of insurance payout amount and frequency associated with the use of atoxigenics. Current RMA premiums were replaced with fair premiums equal to the simulated mean indemnity payment for all crop insurance options. When the treatment scenario was compared to the no treatment scenario, under the set of most efficient crop insurance options, atoxigenic treatment provided the producer with an additional net monetary benefit of $8-$16 per acre.Item Evaluation of Argentine maize hybrids and exotic x temperate testcrosses across environments(Texas A&M University, 2005-11-01) Ochs, Brett AllenMaize (Zea mays L.) is grown in a wide range of environments and altitudes worldwide. Maize has transitioned from open pollinated varieties to single cross hybrids over the last century. While maize production and genetic gain has increased, genetic diversity among U.S. maize hybrids has narrowed. Problems, such as insect pressure, diseases, and mycotoxins, present obstacles for breeders. One approach is to use exotic germplasm in breeding programs to provide useful, novel alleles for productivity, grain quality, and disease resistance. Little exotic germplasm has been used, because of lack of agronomic adaptation and problems with lodging, earliness, and tall plants in more temperate areas. Using exotic elite materials and evaluating them in targeted regions might increase success. Objectives of this research were: to characterize and evaluate agronomic adaptation and performance of Argentine commercial hybrids in the U.S., to evaluate semi-exotic testcrosses developed from semi adapted 100% tropical lines and elite U.S. inbred LH195, and to estimate response to aflatoxin contamination of Argentine hybrids and semi-exotic testcrosses under inoculation with Aspergillus flavus. Agronomic data was collected during 2004 in eleven Texas environments for Argentine hybrids, and eight Texas environments for semi-exotic testcrosses. Response to aflatoxin was measured in three southern Texas environments. U.S. commercial hybrids were used as checks. Significant differences among hybrids were observed for most environments and traits. In general, Argentine hybrids yielded lower, had lower 1000 kernel weights, and greater test weights than U.S. hybrids. Hybrids AX889, AX882MG, and AX890MG were competitive with U.S. hybrids for grain yield and were stable across environments. Semi-exotic testcrosses had similar lodging and grain moisture percentages, heavier test weights and competitive grain yields compared with U.S. hybrids. Hybrid TX-LAMA2002-9-2-B/lH195 had the highest overall grain yield mean for semi-exotic testcrosses and yielded better than two U.S. hybrids. Argentine hybrids had lower aflatoxin concentration than U.S. hybrids; several hybrids had less than 50 ng g-1 aflatoxin. Semi-exotic testcrosses had reduced aflatoxin compared to U.S. hybrids, with several hybrids under 35 ng g-1. These elite, exotic materials show promise for breeding programs, with competitiveness for grain yield, kernel traits, and reduced aflatoxin levels.Item Genotypic and phenotypic characterization of response to aflatoxin and secondary traits in maize(Texas A&M University, 2006-08-16) Edwards, Melanie LoveOne major problem facing maize producers in the southern US is contamination with the mycotoxin aflatoxin, produced by Aspergillus flavus (Link:fr). Aflatoxin is a serious threat to human and animal health, with no resistant commercial hybrid available. Development of resistance to aflatoxin production has several major limitations. Aflatoxin is highly variable both across and within environments, even under inoculation, requiring several locations and replications for breeding. Additionally, there is no screening method that is reliable, rapid, inexpensive, and allows for high throughput. Several secondary traits, such as kernel texture, kernel integrity, husk cover, and visible ear rot, have previously shown to be related to aflatoxin accumulation. These traits are easily characterized in the field and are candidates for indirect selection if they are correlated to aflatoxin concentration. Root lodging, a plant??s inability to maintain upright stature, is another complex characteristic of root related traits that traditionally is selected for indirectly. It can greatly reduce harvestable yield. It is affected by morphological traits and environmental conditions, but its genetic components are little understood. This dissertation comprises three studies presented in chapters II, III, and IV. Chapter II involved white and yellow hybrid maize trials as well as quality protein maize trials from several years across Texas environments. Data was analyzed both per and across location to determine repeatability of response to aflatoxin. Additionally, aflatoxin levels were correlated to several secondary characteristics (female flowering, endosperm texture, husk cover, and ear rot ratings) to determine usefulness in indirect selection. Chapter III was a phenotypic evaluation of a recombinant inbred line (RIL) mapping population, which was derived from divergent parental inbreds Tx811 and CML176. The trials were conducted in two Texas locations, and phenotypic data for aflatoxin concentration, kernel integrity, endosperm texture, female flowering date, and root lodging was collected. Variance components for these traits and genetic and phenotypic correlations were determined. Chapter IV was a genotypic evaluation of the Tx811/CML176 mapping population using simple sequence repeat markers. Genotypic and phenotypic data were combined to identify quantitative trait loci (QTL) and epistatic interactions for response to aflatoxin and for root lodging.Item Layer-by-Layer Assembled Smectite-Polymer Nanocomposite Film for Rapid Detection of Low-Concentration Aflatoxins(2012-11-01) Hu, He 1987-Aflatoxin is a potent biological toxin produced by fungi Aspergillus flavus and A. parasiticus. Current quantification methods for aflatoxins are mostly established on immunoaffinity columns which are both costly and labor intensive. Inspired by smectites? high aflatoxin adsorption capacity and affinity, a novel aflatoxin quantification sensor based on smectite-polyacrylamide (PAM) nanocomposite was fabricated. First, a smectite-PAM nanocomposite film was synthesized on flat silicon substrates which assembled smectite particles from the clay suspension. A layer-by-layer assembly process was developed to achieve uniform morphology and thickness of the nanocomposite films. During the aflatoxin quantification process, positive correlations between the fluorescence intensity from the aflatoxin B1 (AFB1) adsorbed smectite-PAM nanocomposite films and the AFB1 concentration in the test solutions were obtained. The smectite-PAM nanocomposite film has shown similar AFB1 adsorption capabilities as the smectite. Second, the smectite-PAM nanocomposite film was optimized in order to achieve the aflatoxin quantification at ppb level (below 20ppb) in corn extraction solutions. The smectite was modified by Ba2+, which had demonstrated to be able to improve its aflatoxin adsorption capacity. PAM aqueous solutions with the mass concentration ranging from 0.8% to 0.001% were tested. The results showed that the nanocomposite synthesized from 0.005% concentration of PAM solution generated the best properties. After the optimization, the smectite-PAM nanocomposite films achieved the detection of aflatoxin B1, B2, G1 and G2 (AFB2, AFG1 and AFG2) in 10 ppb corn extraction solution. Aflatoxin quantifications in AFB1 and AFB2 mixture solution, AFB1 and AFB2 mixture solution and AFB1 and AFG1 mixture solution were conducted, and the recoveries of last test ranged from 90.52% to 110.11% at low aflatoxin concentration (below 20 ppb). Third, in order to shorten the quantification duration and simplify the detection process, a novel aflatoxin detection array based on smectite-PAM nanocomposite and an improved fluorometric quantification method were developed. Through a microfluidic chip, the reaction time was reduced to 10~20min. Two concentration levels (20~80ppb/5~15ppb) of aflatoxin B1 spiked corn extraction solutions were tested. In the fluorometric quantification step, a common lab-use 365 nm ultraviolet lamp replaced the spectrofluorometer which simplified and accelerated the process.Item Movement and Longevity of Aspergillus flavus Propagules and Factors that Contribute to and Influence their Colonization and Production(2012-10-19) Hassett, BrandonAflatoxin contamination accounts for millions of dollars worth of losses for corn and cotton in Texas. Two atoxigenic strains of Aspergillus flavus, AF36 and Afla-Guard, are labeled for its management. The purpose of this study was to measure differences in the ability of these strains to sporulate and to track movement of their conidia in corn and cotton fields. Sporulation was evaluated by incubating the two strains on their commercial formulations (inoculated on cereal grains) at six constant humidity levels ranging from 0-100%, using closed chambers with saturated salt solutions. Conidial production by Afla-Guard was 3-fold greater than that of AF36 at 100% humidity. Sporulation of the two strains was also evaluated on one substrate by inoculating their conidia on sterile, hulled barley. After 3 days, there was a 234-fold increase in conidia recovered from the barley inoculated with Afla-Guard, compared with a 21-fold increase in conidia recovered from the AF36-inoculated barley. These data suggest that the Afla-Guard strain sporulates better than the AF36 strain, which may be a factor in effectiveness for biological control. An in vitro de-Wit competition experiment showed that sporulation by the Afla-Guard strain was not affected by co-inoculation with either AF36 or the wildtype NRRL3357 toxin producing strain. To measure conidial movement, an Afla-Guard nitrate non-utilizing mutant colonizing autoclaved corn seed, was placed at one point in a field of cotton and corn. For detection, aliquots washed from leaf samples were plated onto a medium containing potassium chlorate. The mutant was recovered at a maximum distance of 6.4 m in corn fields along the same row and as far as 10.2 m across rows from the point source. In cotton fields, the mutant was recovered at 9.1 meters along the same row and 6.1 m across rows from the point source. There was no recovery at 24.3 m from the point source - the maximum distance evaluated. The experiment was repeated in a second year with similar results. These data suggest that plots in field trials may not need wide separation in order to avoid cross contamination. To assess the viability of a toxigenic and atoxigenic strain of A. flavus over time, polycarbonate packets containing conidia and sclerotia of both strains were buried in Ships Clay soil with the matric potential held constant at -24 kPa or -154 kPa. After 10 months, viable conidia were recovered in all treatments. After 14 months, viability of the atoxigenic strain incubated at -154 kPa ?m was lost, while other treatments remained viable. Ears of corn were inoculated via silk channel at different stages of silk senescence. Sclerotia were enumerated from the same plants following harvest of the crop. Sclerotial production by A. flavus was greatest from ears with silks inoculated at senescence, compared with inoculation when silks were green. The isolation frequency of Penicillium sp. from surface-sterilized kernels at harvest was the highest from ears that were inoculated with A. flavus when silks were fresh, as compared with A. flavus inoculation of ears with senescent silks. A Fusarium and Penicillium species was isolated from harvested kernels, and their sterile Czapek-Dox broth culture filtrates were tested for their effect on development of three strains of A. flavus on agar. The Penicillium broth filtrate greatly reduced sclerotial numbers relative to the control and the Fusarium filtrate (P<0.05). When A. flavus was grown in the presence of autoclaved Penicillium culture filtrate, there was no effect on sclerotial production. The Penicillium filtrate increased the rate of radial hyphal growth of the A. flavus isolates on agar compared to the control and the Fusarium culture filtrate. ?Item Multi-Location Evaluation of Agronomic Traits in Maize Hybrids(2012-12-12) McKee, Michael 1982-Maize (Zea mays L.) is one of the main crops grown in the United States. Genetic improvement over the last century has seen a shift from using open-pollinated varieties to single cross hybrids. This has resulted in major grain yield gains and improved management methodologies. However, there is still concern about reduced genetic diversity in elite corn germplasm and the potential effects this could have on future maize productivity in the presence of numerous abiotic and biotic pressures. One solution to this issue is the incorporation of exotic germplasm into existing maize improvement programs. This exotic material must be evaluated and characterized because too much or poorly matched exotic material can lead to reduced productivity. The use of multiple environments representative to the target improvement area is the best way to determine the true potential of certain material. The objectives of this research were to: i) estimate the responses of hybrids to aflatoxin and their agronomic performance across a range of environments under inoculation with Aspergillus flavus; ii) identify the hybrids within each group that exhibit the lowest levels of contamination; iii) analyze the relationship between agronomic performance and aflatoxin accumulation; and iv) determine how Genotype x Environment interactions affect these traits. Agronomic data was collected in ten Texas environments in 2005 for hybrids created from yellow, white, and Quality Protein Maize material that was crossed with one of two elite temperate inbred testers, LH195 or LH210. Response to aflatoxin was measured in eight of these environments. U.S. commercial hybrids were used as checks. Significant differences between hybrids were observed at different environments for different traits. Overall the experimental hybrids had lower aflatoxin accumulation than the commercial checks. They also yielded lower and had lower test weights and 1000 kernel weights. However, there were some hybrids that were competitive with the commercial checks for these agronomic traits. The incorporation of this material into established U.S. lines could be beneficial with regards to aflatoxin accumulation and kernel quality, which could ultimately translate to higher yields and crop quality.Item Phenotypic and genotypic characterization of high lysine maize(Texas A&M University, 2006-04-12) Bhatnagar, SandeepQuality Protein Maize (QPM) with the mutant gene opaque-2 (o2), has higher lysine and tryptophan content and hard endosperm which is less susceptible to mechanical and biological damage. Three experiments were conducted to characterize the phenotypic and genotypic characteristics of high lysine maize. In the first experiment two separate diallels including 7 white and 9 yellow QPM inbreds were evaluated in five southern USA environments to estimate the general (GCA) and specific combining abilities (SCA) for grain yield and to identify potential heterotic relationships among them. QPM hybrids yielded less than commercial checks. GCA effects across environments were non-significant for grain yield but highly significant for secondary traits. Best yielding hybrids resulted from crosses among inbreds from different programs (CIMMYT, Mexico; University of Natal, South Africa and TAMU, USA). In the second experiment testcrosses between QPM inbreds and Tx804, were evaluated for agronomic performance, aflatoxin resistance and quality. QPM inbreds in testcrosses have similar flowering dates, plant height, ear height and test weights but lower grain yield than normal checks. Population 69 inbreds and their testcrosses were least susceptible to aflatoxin. Aflatoxin in testcrosses was positively correlated with endosperm texture (0.67) and kernel integrity (0.60) but negatively correlated with grain yield (-0.30) and silking date (-0.50). Tryptophan content was negatively correlated with endosperm modification. Amino acid levels of inbred lines were significantly correlated with those of hybrids, but with low predictive value. In the third experiment 92 high lysine maize inbreds with different origins [Stiff Stalk, Non Stiff Stalk, Pop 69, temperate (Tx802, Tx804, Tx806, B97, B104) and exotic subtropical lines (CML161, Do940y and Ko326y)] were haplotyped on a cM scale utilizing 43 mapped SSR markers to characterize genetic diversity on chromosome 7, estimate linkage disequilibrium around opaque-2 locus and determine the parental contribution in some inbreds. Dendrograms of genetic similarity showed clusters in agreement with the different origin of inbreds. A total of 200 alleles were detected with an average of 4.7 alleles/locus. Significant linkage disequilibrium was detected around opaque-2 locus. Parental contributions of haplotypes showed segments of chromosome 7 exclusively contributed by one or the other parent.Item Response to aflatoxin and grain composition of exotic maize germplasm(2009-06-02) Corn, Rebecca JoannExotic germplasm has potential to provide new alleles for disease and insect resistance. US maize (Zea mays L.) currently lacks genetic resistance to Aspergillus flavus, a fungal pathogen that produces aflatoxin in maize kernels. Aflatoxin is one of the main limitations to maize production in hot, dry regions like the Southern US because of the harmful effects on humans and animals and subsequent marketing regulations. Two experiments were conducted to evaluate different exotic maize collections for response to aflatoxin. Exotic adapted maize lines, known as LAMA lines, were found to accumulate less aflatoxin than US hybrids in tests across Southern Texas. Exotic introgression lines developed by The International Center for Maize and Wheat Improvement (CIMMYT) including inbred lines, yellow hybrids, and white hybrids, were more resistant to aflatoxin than US inbred lines and hybrids in field trials in Texas, Georgia, and Mississippi. Another experiment evaluated the grain composition of hybrids with exotic adapted LAMA maize lines and a collection of US hybrids, quality protein maize (QPM) hybrids, and advanced breeding lines using near-infrared spectroscopy. Individual LAMA lines and advanced breeding lines have higher starch content than US hybrid checks. Starch content was the primary grain composition trait of interest as an enhanced-value market has emerged for high starch maize hybrids. Limited germplasm has been analyzed for grain composition because wet chemistry analysis methods required large sample sizes and were time and labor intensive. The near infrared spectroscopy (NIR) method requires a relatively small sample and is a non-destructive analysis method. In this study, NIR was effective at ranking genotypes based on starch, oil, and protein content of the grain.Item Unraveling Reciprocal Lipid-Mediated Communication between Maize Seed and Aspergillus flavus(2014-07-31) Borrego, Eli JamesIt is generally accepted, that the reciprocal exchange of molecules between plants and fungi govern the outcome of their interaction. From a multitude of potential signals, one class of oxidized lipids (oxylipins) has taken central stage in this concept. Synthesized from enzymatic and non-enzymatic peroxidation of fatty acids, oxylipins are a large and diverse group of potent endogenous signaling molecules. Because plant and fungal oxylipins are similar biochemically and structurally, a novel hypothesis has emerged that during plant-fungal interactions, that these metabolites are exchanged, perceived, and affect the behavior of opposing partner. This study sought to explore this hypothesis and assign a role to specific oxylipin-producing enzymes from maize and Aspergillus flavus within the context of the oxylipin-mediated cross-kingdom crosstalk. Maize wild-type and near-isogenic mutants for several lipoxygenase (LOX) and 12-oxophytodienoate reductases (OPR) related to jasmonic acid biosynthesis and nine oxylipin-mutant strains of Aspergillus flavus were utilized to investigate the contribution of oxylipins from the plant and the fungi on fungal ability to colonize the host, sporulate and produce aflatoxin. Phytohormone content and gene expression analyses of infected seed were preformed to explore potential associations of defense hormones with fungal pathogenesis processes. Results showed that several genes involved in JA biosynthesis affect specific fungal processes. Despite belonging to separate subgroups, both LOX3 and LOX7 are involved in defense against colonization. Additionally, LOX3 expression correlates negatively with colonization and lox3 knockout mutants are more susceptible regardless of the fungal genotype indicating a general defensive role for LOX3 against A. flavus colonization. An unexpected major finding from this study is that JA biosynthesis genes appear to promote aflatoxin accumulation. Results provide evidence that the fungal LOX gene is required for normal colonization of seed, while PpoA is required for normal conidia and aflatoxin production. The ratio of ABA/JA correlates positively with aflatoxin accumulation. These findings are expected to expedite studies of seed-fungal interactions, lead to uncovering novel regulators of seed defense, find specific host genes and signals that regulate conidiation and mycotoxin production, and eventually provide the maize industry with genetic targets and biochemical markers for selecting aflatoxin resistant lines.