Smectite clay has been shown in studies over the past 20 years to sorb aflatoxin B1 (AfB1) in animal feed and thereby reduce its toxic influence on animals. In this study, 20 smectite samples were selected from industrial products or reference minerals. In the initial steps, it was shown that AfB1 entered the interlayer galleries of smectites and a 10-fold range in sorption ability was observed in a set of 20 smectite samples. Yet, it was not clear which clay properties (CEC, pH, base saturation) influenced this variation. In an effort to further explore properties that might influence the sorption of AfB1, three good sorbent samples were chosen from our set of 20 samples along with one sample of low sorption capacity. Those samples were fractionated into sand, silt, coarse clay (CC), and fine clay (FC) fractions. From all sample fractions, sorption isotherms and X-ray diffraction patterns were obtained. Additionally, a vermiculite and a palygorskite were examined with regard to sorption capacity. Concentration of smectite and their adsorption test suggest that differences in smectite composition are responsible for difference in sorption, not so much their relative abundance or other mineral phases. Initial infrared analysis indicates that weathered aluminous smectites, which have no octahedral iron or magnesium, belong to the poor AfB1 sorbents. Palygorskite and vermiculite are not effective sorbents. Based on the findings in this study, tentative quality criteria of sorbent selection for their use in animal feed were established. These criteria are: pH between 6.5 and 8.5, CEC > 75cmolc/kg, organic carbon < 2.5 g/kg, expression of XRD smectite peak and AlFeOHbending in FTIR and Langmuir adsorption capacity for AfB1 > 0.40 mol/kg.

Maize 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.

Quality 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.

Improving food safety and food security is imperative to adequately feed a growing population that is expected to exceed 9 billion people by 2050. Mushroom cultivation provides unique opportunities to take advantage of underutilized resources and produce high-quality food from otherwise inedible or unsafe food sources. Pleurotus ostreatus is a ligninolytic and biotechnologically relevant fungus that can be cultivated on a diverse array of lignocellulosic byproducts. Prosopis spp. are abundant in the Sonoran Desert and broadly distributed in semi-arid to arid regions around the globe. Prosopis spp. legumes (pods), and approximately 25% of all commonly cultivated crops, are susceptible to aflatoxin contamination, a highly carcinogenic and potentially lethal mycotoxin. This work aimed to (1) identify novel lignocellulosic byproducts from the Sonoran Desert for use as substrate materials in Pleurotus ostreatus (oyster mushroom) cultivation; (2) evaluate the safety of mushrooms cultivated on plant products that are contaminated with aflatoxin; and (3) measure the amount of aflatoxin that is degraded by P. ostreatus after the contaminated products have been colonized by the fungus. Prosopis spp. pods were identified as suitable substrate component for P. ostreatus production by conducting yield evaluations and finding that the biological efficiency increased with increasing percentages of pods. No detectable quantity of aflatoxin could be measured in mushrooms that were cultivated on maize that was naturally contaminated with aflatoxin B1 at concentrations up to 2500 ng g⁻¹. P. ostreatus degraded AFB₁ by >85% in maize with initial concentrations of 2500 ng g⁻¹ AFB₁ in repeated experiments. Thus, the cultivation of P. ostreatus on aflatoxin-contaminated products may be a viable method to produce a safe and high quality food from an otherwise unsafe food source, and may double as a means to reduce the aflatoxin concentration in contaminated plant products to levels that are acceptable for use as livestock feed.

Aflatoxin is a carcinogenic mycotoxin. Aflatoxin contamination of susceptible crops is the product of communities of Aspergillus section Flavi and average aflatoxin-producing potential of these communities influence aflatoxin contamination risk. In 2004 and 2005, Sugarcane producing counties in the Rio Grande Valley of Texas (RGV) had unique aflatoxin-producing communities containing Aspergillus parasiticus. Sugarcane fields or those rotated for less than two years had Aspergillus section Flavi communities dominated by A. parasiticus. A. parasiticus was rarely detected in long-term rotation fields and not detected in counties without sugarcane crops. Aflatoxin-producing fungi infecting RGV sugarcane stems ranged from 52 - 95% A. parasiticus in hand-collected samples and billets for commercial planting, respectively. Identical A. parasiticus fungi found in Japan caused aflatoxin contamination of raw sugar there. Population genetics and phylogenetics were used to characterize a global sampling of 112 A. parasiticus and identify geographic distributions and crop associations within the species. One population shows clear association with sugarcane and is distributed to Asia, Africa and North America, implicating human involvement in its distribution. A. parasiticus populations from maize and peanut have broad geographic distribution but crop specific lineages and/or populations were not detected. One A. parasiticus population isolated from maize has a distribution limited to Mexico. A phylogeny generated from a partial nitrate reductase gene resolves a lineage that correlates with the sugarcane population and suggests crop association and geographic distribution may drive divergence within A. parasiticus. Crop associations shape fungal communities and must be considered for aflatoxin management. Native food enthusiasts in Arizona conduct public millings of wild- and landscape-collected mesquite pods (Prosopis spp.) to produce mesquite flour, which is often consumed in the same localities where it is produced without conventional food safety inspection. Aflatoxin was found in imported, domestic, and non-commercial mesquite flour batches, with 10% above the FDA action level for human food (>20 ppb), and 95% could not be exported to Europe (>2 ppb). Aflatoxin content in Tucson was largely explained (63%) by harvest date with those harvested later yielding more aflatoxin. Lateral flow aflatoxin assay of mesquite flour proved viable for lab and public testing.

The principal objective of this investigation was to evaluate the effects of mycotoxin contaminated diets (deoxynivalenol (DON)), aflatoxin B1 (AFB1), and fumonisin (FUM)), with or without the use of a commercially available deactivating compound (DC), in young pullets and replacement laying hens on performance, reproductive, serological, and histopathological parameters. In trial 1, experimental treatments consisted of control, low toxin (1 µg DON/g + 1 µg AFB1/g), and high toxin (2 µg DON/g + 2 µg AFB1/g) diets. Pullets fed the high toxin diet had reduced (P<0.05) body weights compared to control and low toxin diets at d 14, 35, 49, 56, and 63. At d 21 and 28, there was a significant interaction observed between mycotoxin and DC inclusion in body weights. Following necropsies (d 35 and 65), relative liver weights and histopathological liver tissue damage were increased (P<0.05) in pullets fed high toxin diets when compared to control and low toxin diets. Relative kidney weights were increased (P<0.05) due to high toxin diet at d 65. Expected negative effects of toxin administration on titer development were not observed. The only interaction observed between mycotoxin administration and DC inclusion in trial 1 was on body weights. In trial 2, experimental treatments consisted of control, DON (9 µg/g) challenge, AFB1 (2 µg/g) + FUM (54 µg/g) challenge, and a mixed challenge (6 µg DON/g, 1 µg AFB1/g, and 27 µg FUM/g). All mycotoxin diets fed to hens negatively influenced (P<0.05) feed efficiency for the trial period spanning weeks 6 through 10 when compared to control diets. Egg production was not affected (P>0.05) by all mycotoxin diets weeks 6 through 10. Relative weights of the liver and kidney were increased (P<0.05) by AFB1+FUM challenge weeks 4 and 9 compared to control diet. The data reported in this study demonstrate that dietary DON and / or AFB1+FUM influence some performance, reproductive, histopathological, and egg quality traits, but by and large, replacement layer pullets seem to be relatively resistant to the mycotoxins evaluated in this trial at the described levels of administration.

Aflatoxin 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 ψm 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.

Zugl.: Aachen, Techn. Hochsch., Diss., 2007

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 83-96).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 64-83).