Research Note: Orange corn altered the cecal microbiome in laying hens.

Carotenoids, which are pigments known to have many health benefits, such as their antioxidant properties, are being researched for their potential as a feed additive for production animals. These pigments are found in varying quantities in different breeds of corn, and their impact on the chicken microbiome requires further investigation. This 35 d laying hen (Novagen White) feeding trial involved varying the levels and composition of carotenoids by changing the corn source: white (0.9 µg total carotinoids/g total diet), yellow (5.7 µg/g), and orange (24.9 µg/g). For each of the three corn diet treatments, 6 replicate cages were randomly assigned. The cecal microbial community composition of the hens was then studied by 16S rRNA gene amplicon sequencing. The composition of the cecal bacterial community, as determined by Bray-Curtis dissimilarity, was different (P < 0.05) in chickens fed the orange corn diet, compared to chickens on the white corn diet, but there was no statistical difference between animals fed yellow corn compared to the white or orange corn groups. There was no change in the alpha diversity between any of the groups. Within Lactobacillus, which is one of the most abundant genera, 2 amplicon sequence variants (ASVs) were decreased and one ASV was increased in the orange corn group compared to both the white and yellow corn groups. While previous studies showed that orange corn did not alter the community composition in broilers, it appears that orange corn based feed may alter the community composition of laying hens.

Orange corn diets associated with lower severity of footpad dermatitis in broilers.

Footpad dermatitis (FPD), damage and inflammation of the plantar surface of the foot, is of concern for poultry because FPD affects the birds' welfare and production value. Footpad dermatitis is painful and causes costly chicken paw downgrades, carcass condemnations, and reduced live weights. However, a universal preventative has not been found. The hypothesis was that diets containing orange corn, when compared with diets containing yellow or white corn, would reduce the severity of footpad dermatitis in broiler chickens on wet litter. When compared with yellow and white corn, orange corn contains higher quantities of carotenoids, antioxidant pigments, believed to play a role in skin and feather health. This experiment was a randomized block, 3 × 2 factorial design: orange, yellow, and white corn diets with birds raised on wet or dry litter (control group). Female Ross 708 broilers (n = 960) were used to create 4 replicates of each diet x litter treatment combination. Footpads were scored at day 19, 27, 35, and 42, following the Global Animal Partnership standard's 0-2 scale of visual increasing severity: 0 indicates minimal damage and 1 and 2 indicate mild to severe lesions and ulceration, dark papillae, and/or bumble foot. At 42 d of age, birds on the wet litter had greater severity of FPD, scores 1 and 2, compared with the control group (88 vs. 13% respectively; P < 0.0001). At 42 d of age, prevalence of more severe footpad scores, 1 or 2, was lowest on the orange corn diet (33%), followed by white corn (56%) and yellow corn (63%). Birds fed the orange corn diet had higher BW throughout the study (P = 0.004) and had fat pads and livers with higher yellow pigment deposition (P < 0.005). Litter moisture content altered microbiome composition but corn type did not. In conclusion, the main determinant of FPD in this study was exposure to wet litter. When compared with yellow and white corn, orange corn was associated with improved bird growth and reduced severity of footpad dermatitis, especially at later time points.

ß-Cryptoxanthin biofortified maize (Zea mays) increases ß-cryptoxanthin concentration and enhances the color of chicken egg yolk.

The laying hen has a natural ability to deposit carotenoids into its egg yolks, especially the xanthophyll carotenoid lutein that is used commercially as an egg colorant. Can this ability to deposit carotenoids be used to enrich egg yolk provitamin A value? After a 10-d carotenoid depletion period in hens (n = 24), the effects of a 20-d intervention with high-ß-cryptoxanthin, high-ß-carotene, or typical yellow maize on color and carotenoid profile were compared with the effects of a white maize diet (n = 6/treatment). Eggs were collected every other day and yolks were analyzed by using a portable colorimeter to define the color space and by using an HPLC to determine the carotenoid profile. The high-ß-cryptoxanthin and yellow maize increased ß-cryptoxanthin in the yolk (0.55 ± 0.08 to 4.20 ± 0.56 nmol/g and 0.55 ± 0.08 to 1.06 ± 0.12 nmol/g, respectively; P < 0.001). Provitamin A equivalents increased in eggs from hens fed high-ß-cryptoxanthin maize (P < 0.001) but not the high-ß-carotene maize. The color (L*, a*, and b*) assessment of the yolks showed an increase in the high-ß-cryptoxanthin treatment for the red-green a* scale (P < 0.001) and a decrease for the light-dark L* scale (P < 0.001). No appreciable change was noted in the yellow-blue b* scale for the high-ß-cryptoxanthin treatment; but significant changes were noted for the yellow (P = 0.002) and high-ß-carotene maize (P = 0.005) treatments, which were most evident at the end of the washout period with white maize. ß-Cryptoxanthin-biofortified maize is a potential vehicle to elevate provitamin A equivalents and to enhance the color of yolks. This could lead to a human health benefit if widely adopted.

The relationship between parental genetic or phenotypic divergence and progeny variation in the maize nested association mapping population.

Appropriate selection of parents for the development of mapping populations is pivotal to maximizing the power of quantitative trait loci detection. Trait genotypic variation within a family is indicative of the family's informativeness for genetic studies. Accurate prediction of the most useful parental combinations within a species would help guide quantitative genetics studies. We tested the reliability of genotypic and phenotypic distance estimators between pairs of maize inbred lines to predict genotypic variation for quantitative traits within families derived from biparental crosses. We developed 25 families composed of ~200 random recombinant inbred lines each from crosses between a common reference parent inbred, B73, and 25 diverse maize inbreds. Parents and families were evaluated for 19 quantitative traits across up to 11 environments. Genetic distances (GDs) among parents were estimated with 44 simple sequence repeat and 2303 single-nucleotide polymorphism markers. GDs among parents had no predictive value for progeny variation, which is most likely due to the choice of neutral markers. In contrast, we observed for about half of the traits measured a positive correlation between phenotypic parental distances and within-family genetic variance estimates. Consequently, the choice of promising segregating populations can be based on selecting phenotypically diverse parents. These results are congruent with models of genetic architecture that posit numerous genes affecting quantitative traits, each segregating for allelic series, with dispersal of allelic effects across diverse genetic material. This architecture, common to many quantitative traits in maize, limits the predictive value of parental genotypic or phenotypic values on progeny variance.

Proteomic analysis of early germs with high-oil and normal inbred lines in maize.

High-oil maize as a product of long-term selection provides a unique resource for functional genomics. In this study, the abundant soluble proteins of early developing germs from high-oil and normal lines of maize were compared using two-dimensional gel electrophoresis (2-DGE) in combination with mass spectrometry (MS). More than 1100 protein spots were detected on electrophoresis maps of both high-oil and normal lines by using silver staining method. A total of 83 protein spots showed significant differential expression (>two-fold change; t-test: P < 0.05) between high-oil and normal inbred lines. Twenty-seven protein spots including 25 non-redundant proteins were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS). Functional categorization of these proteins was carbohydrate metabolism, cytoskeleton, protein metabolism, stress response, and lipid metabolism. Three such proteins involved in lipid metabolism, namely putative enoyl-ACP reductase (ENR), putative stearoyl-ACP desaturase (SAD) and putative acetyl-CoA C-acyltransferase (ACA), had more abundant expressions in high-oil lines than in normal. At the mRNA expression level, SAD, ENR and ACA were expressed at significantly higher levels in high-oil lines than in normal. The results demonstrated that high expressions of SAD, ENR and ACA might be associated to increasing oil concentration in high-oil maize. This study represents the first proteomic analysis of high-oil maize and contributes to a better understanding of the molecular basis of oil accumulation in high-oil maize.

Using molecular markers to identify two major loci controlling carotenoid contents in maize grain.

Maize is an important source of pro-vitamin A; beta-carotene, alpha-carotene and beta-cryptoxanthin, and the non-pro-vitamin A carotenoids including lutein and zeaxanthin. In the present study, a recombinant inbred (RI) population with 233 RI lines derived from a cross between By804 and B73 was employed to detect QTL for these nutritionally important components in maize grain. High Performance Liquid Chromatography was used to measure amounts of individual carotenoids over 2 years. A genetic linkage map was constructed with 201 molecular markers. In all, 31 putative QTL including 23 for individual and 8 for total carotenoids were detected on chromosome(s) 1, 3, 5, 6, 7, 8 and 10. The notable aspect of this study was that much of the phenotypic variation in contents of carotenoids could be explained by two loci (y1 and y9), and the QTL for carotenoids elucidated the interrelationships among these compounds at the molecular level. A gene targeted marker (Y1ssr) in the candidate gene phytoene synthase 1 (psy1) tightly linked to a major QTL explaining 6.6-27.2% phenotypic variation for levels of carotenoids was identified, which may prove useful to expedite breeding for higher level of carotenoids in maize grain. This functionally characterized gene (psy1) could also be exploited for further development of functional marker for carotenoids in maize. The QTL cluster located at y9 locus may also be used for pyramiding favorable alleles controlling contents of carotenoids from diverse maize germplasm.

Quantitative trait loci analysis of phenotypic traits and principal components of maize tassel inflorescence architecture.

Maize tassel inflorescence architecture is relevant to efficient production of F(1) seed and yield performance of F(1) hybrids. The objectives of this study were to identify genetic relationships among seven measured tassel inflorescence architecture traits and six calculated traits in a maize backcross population derived from two lines with differing tassel architectures, and identify Quantitative Trait Loci (QTL) involved in the inheritance of those tassel inflorescence architecture traits. A Principal Component (PC) analysis was performed to examine relationships among correlated traits. Traits with high loadings for PC1 were branch number and branch number density, for PC2 were spikelet density on central spike and primary branch, and for PC3 were lengths of tassel and central spike. We detected 45 QTL for individual architecture traits and eight QTL for the three PCs. For control of inflorescence architecture, important QTL were found in bins 7.02 and 9.02. The interval phi034-ramosa1 (ral) in bin 7.02 was associated with six individual architecture trait QTL and explained the largest amount of phenotypic variation (17.3%) for PC1. Interval bnlg344-phi027 in bin 9.02 explained the largest amount of phenotypic variation (14.6%) for PC2. Inflorescence architecture QTL were detected in regions with candidate genes fasciated ear2, thick tassel dwarf1, and ral. However, the vast majority of QTL mapped to regions without known candidate genes, indicating positional cloning efforts will be necessary to identify these genes.

Genetic and QTL analysis of maize tassel and ear inflorescence architecture.

Maize (Zea mays L.) ear inflorescence architecture is directly relevant to grain yield components, and tassel architecture is relevant to hybrid seed production. The objectives of this study were to (1) determine heritabilities and correlations of a comprehensive set of tassel and ear inflorescence architecture traits in a set of (Illinois Low ProteinxB73) B73 S1 families, (2) identify chromosomal positions of QTL affecting tassel and ear architecture, and (3) identify possible candidate genes associated with these QTL. For tassel traits, the number of detected QTL ranged from one to five, and explained between 6.5 and 35.9% of phenotypic variation. For ear traits, the number of detected QTL ranged from one to nine and phenotypic variation explained by those QTL varied between 7.9 and 53.0%. We detected QTL for tassel architecture traits that required calculation of ratios from measured traits. Some of these calculated traits QTL were detected in regions that did not show QTL for the measured traits, suggesting that calculation of ratios may reveal developmentally relevant patterns of tassel architecture. We detected a QTL on chromosome 7 for tassel branch number near the gene ramosa1 (ra1), which is known to control tassel branch number, making ra1 a candidate gene for tassel branch number. We detected QTL for several traits on chromosomes 6, 8, and 9, where no inflorescence architecture genes have been mapped, thus providing initial information towards new gene discovery for control of inflorescence architecture.

QTL and candidate genes phytoene synthase and zeta-carotene desaturase associated with the accumulation of carotenoids in maize.

Carotenoids are a class of fat-soluble antioxidant vitamin compounds present in maize ( Zea mays L.) that may provide health benefits to animals or humans. Four carotenoid compounds are predominant in maize grain: beta-carotene, beta-cryptoxanthin, zeaxanthin, and lutein. Although beta-carotene has the highest pro-vitamin A activity, it is present in a relatively low concentration in maize kernels. We set out to identify quantitative trait loci (QTL) affecting carotenoid accumulation in maize kernels. Two sets of segregating families were evaluated-a set of F2:3 lines derived from a cross of W64a x A632, and their testcross progeny with AE335. Molecular markers were evaluated on the F2:3 lines and a genetic linkage map created. High-performance liquid chromatography was performed to measure beta-carotene, beta-cryptoxanthin, zeaxanthin, and lutein on both sets of materials. Composite interval mapping identified chromosome regions with QTL for one or more individual carotenoids in the per se and testcross progenies. Notably QTL in the per se population map to regions with candidate genes, yellow 1 and viviparous 9, which may be responsible for quantitative variation in carotenoids. The yellow 1 gene maps to chromosome six and is associated with phytoene synthase, the enzyme catalyzing the first dedicated step in the carotenoid biosynthetic pathway. The viviparous 9 gene maps to chromosome seven and is associated with zeta-carotene desaturase, an enzyme catalyzing an early step in the carotenoid biosynthetic pathway. If the QTL identified in this study are confirmed, particularly those associated with candidates genes, they could be used in an efficient marker-assisted selection program to facilitate increasing levels of carotenoids in maize grain.

Sequence variation and genomic organization of fatty acid desaturase-2 (fad2) and fatty acid desaturase-6 (fad6) cDNAs in maize.

Increased levels of oleic acid may enhance the nutritional and functional value of corn. Corn oil is primarily composed of palmitic, stearic, oleic, linoleic and linolenic fatty acids. Delta-12 desaturase in plants converts oleic acid (18:1) to linoleic acid (18:2) by inserting a double bond at the delta-12 position. Fatty acid desaturase-2 (fad2) encodes delta-12 desaturase that functions in the endoplasmic reticulum while fatty acid desaturase-6 (fad6) encodes delta-12 desaturase that functions in plastids. Complementary DNA (cDNA) clones from putative maize homologs for fad2 and fad6 were identified and the entire clones DNA sequenced. The maize fad2 cDNAs showed an amino-acid identity of 67-77% to fad2 of Glycine, Arabidopsis and Brassica species. Our cDNA sequence comparisons suggested that more than one fad2 gene is transcribed in maize embryos. Two different fad2 cDNAs from an embryo cDNA library map to separate chromosomal positions, providing evidence consistent with two different isoforms of fad2 expressed in the embryo. The fad2 cDNAs from multiple tissue sources clustered into three groups on a phenogram, and map to different positions on chromosomes 4, 5 and 10, which suggests at least three different isoforms of fad2 may be expressed in the maize plant. The two maize fad6 cDNAs share 81% amino-acid identity with the Arabidopsis fad6 and map to chromosome 1. Northern analysis revealed that fad2 is transcribed in embryos at 14, 21, 28 and 35 days after pollination, with the highest level observed at day 14. None of the fad2 or fad6 clones mapped to maize chromosome bins associated with QTLs for the ratio of oleic/linoleic acid, notably bin 6.04 which contains the linoleic1 locus and the largest reported QTL for the oleic/linoleic ratio. This suggests, but does not prove, that some of the QTLs for the oleic/linoleic acid ratio do not involve allelic variants of fad2 or fad6 but rather involve other genes that may influence flux through the enzymes encoded by fad2 or fad6.

Quantitative trait loci for low aflatoxin production in two related maize populations.

Aflatoxin B(1) formed by Aspergillus flavus Fr:Link has been associated with animal disease and liver cancer in humans. We performed genetic studies in progenies derived from maize inbred Tex6, associated with relatively low levels of aflatoxin production, crossed with the historically important inbred B73. (Tex6 x B73) x B73 BC(1)S(1) and Tex6 x B73 F(2:3) mapping populations were produced and evaluated in 1996 and 1997 in Champaign, Ill. Ears were inoculated 20 to 24 days after midsilk using a pinboard method and a mixture of conidia of A. flavus Link:Fr. isolates. Aflatoxin B(1) levels in harvested ears were determined using an indirect competitive ELISA. Molecular markers were assayed on the populations and used to generate maps. Molecular marker - QTL associations for lower levels of aflatoxin production were determined using multiple regression (MR) and composite interval analysis with multiple regression (CIM MR). MR revealed sets of markers associated with lower aflatoxin production in 1996 and 1997, and CIM MR detected a smaller subset of loci significant in 1997. QTLs for lower aflatoxin were attributed to both Tex6 and B73 parental sources. Environment strongly influenced the detection of QTLs for lower aflatoxin production in different years. There were very few chromosome regions associated with QTLs in more than 1 year or population with MR analysis, and none with CIM MR analysis. In 1997, QTLs for lower aflatoxin were detected with CIM MR in bins 5.01-2 and 5.04-5 in the BC(1)S(1) population, and in bins 3.05-6, 4.07-8 and 10.05-10.07 in the F(2:3) population. These QTL associations appear the most promising for further study.

Quantitative trait loci influencing chemical and sensory characteristics of eating quality in sweet corn.

This study was conducted to ascertain the chromosomal location and magnitude of effect of quantitative trait loci (QTL) associated with the chemical and sensory properties of sweet corn (Zea mays L.) eating quality. Eighty-eight RFLPs, 3 cloned genes (sh1, sh2, and dhn1), and 2 morphological markers (a2 and se1) distributed throughout the sweet corn genome were scored in 214 F2:3 families derived from a cross between the inbreds W6786su1Se1 and IL731Asu1se1. Kernel properties associated with eating quality (kernel tenderness and starch, phytoglycogen, sucrose, and dimethyl sulfide concentrations) were quantified on F2:3 sib-pollinated ears harvested at 20 days after pollination. Sensory evaluation was conducted on a subset of 103 F2:3 families to determine intensity of attributes associated with sweet corn eating quality (corn aroma, grassy aroma, sweetness, starchiness, grassy flavor, crispness, tenderness, and juiciness) and overall liking. Single factor analysis of variance revealed significant QTL for all these traits, which accounted for from 3 to 42% of the total phenotypic variation. A proportion of the RFLP markers associated with human sensory response were also found to be associated with kernel characteristics. To our knowledge this is the first report of the identification of QTL associated with human flavor preferences in any food crop. Key words : sweet corn, RFLP, quantitative trait loci, eating quality, sensory evaluation.

Comparison of RAPD and RFLP markers for mapping F2 generations in maize (Zea mays L.).

The F2 generations from two maize crosses were used to compare the ability of RAPD and RFLP marker systems to create a genetic linkage map. Both RFLPs and RAPDs were shown to provide Mendelian-type markers. Most of the RFLPs (80%) could be placed with a good level of certainty (LOD>4) on the genetic linkage map. However, because of their dominant nature, only between 37% and 59% of the RAPDs could be placed with such a LOD score. The use of combined data from RFLPs and RAPDs increases the level of information provided by RAPDs and allows the creation of a combined RFLP/RAPD genetic linkage map. Thus, the RAPD technique was found to be a powerful method to provide improved probes coverage on a previously created RFLP map and to locate markers linked to chromosomal regions of interest.

Change in ribosomal DNA spacer-length composition in maize recurrent selection populations. 2. Analysis of BS10, BS11, RBS10, and RSSSC.

Four maize (Zea mays L.) populations selected for grain yield (BS10, Iowa Two-ear Synthetic; BS11, formerly Pioneer Two-ear Composite; RBS10, Illinois strain of BS10; and RSSSC, Illinois strain of Iowa Stiff Stalk Synthetic) were assayed for molecular variation in the ribosomal DNA (rDNA) intergenic spacer (IGS) at initial and advanced cycles of selection. RSSSC and RBS10 underwent reciprocal recurrent selection with an inbred tester in a high-yield environment, whereas BS10 and BS11 were subjected to full-sib reciprocal recurrent selection. Maize rDNA, which encodes the ribosomal RNA genes, is highly repetitive and shows IGS length variation within and among individuals. Five different ribosomal spacer-length variants (rslvs) and a polymorphic SstI restriction site in the IGS were detected in the four populations. The five rslvs and the polymorphic restriction fragment were observed in 20 different combinations or hybridization fragment patterns (HP). RSSSC, RBS10, and BS11 showed significant changes in the overall rslv and HP frequencies between cycle 0 and the advanced cycle of selection, whereas BS10 did not. In general, two specific HPs were more frequent in the majority of the advanced cycles of the four populations. The frequency changes between initial and advanced cycles were more dramatic for HPs than rslvs. These results are consistent with earlier findings and further support the hypothesis that certain rDNA HPs and/or linked loci may be responding to selection for grain yield and may be associated with a selective advantage in US Corn Belt environments.

Quantitative trait locus analysis of fatty acid concentrations in maize.

A study was conducted to determine the number and chromosomal location of quantitative trait loci (QTL) influencing the concentration of five fatty acids in 200 F2S1 lines derived from an Illinois High Oil (IHO) by Illinois Low Oil (Early Maturity) (ILO(EM)) cross. Restriction fragment length polymorphism (RFLP) analysis was performed on the 200 S1 lines and concentrations of palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic (18:3) acids were determined in self-pollinated kernels harvested from plants grown in replicated field trials during 1992 and 1993. A series of 74 cDNA and genomic clones were used and these revealed 80 polymorphic loci spaced, on average, 24 cM apart throughout the maize genome. Analysis of variance detected significant (p < 0.05) associations between several RFLP loci and the concentration of each fatty acid. A total of 15 RFLP loci clustered in 12 chromosomal regions were associated with the concentration of 16:0, 17 loci clustered in 10 regions were associated with the concentration of 18:0, 12 loci clustered in eight regions were associated with the concentration of 18:1 and 18:2, and 17 loci clustered in eight regions were associated with the concentration of 18:3. Multiple linear regression models consisting of four RFLP loci explained 24 and 62% of the total phenotypic and genotypic variation (R2) among the 200 F2S1 lines for 16:0, five loci explained 51 and 71% of the variation for 18:0, three loci explained 67 and 79% of the variation for 18:1, two loci explained 67 and 81% of the variation for 18:2, and seven loci explained 52 and 78% of the variation for 18:3 in these 200 F2S1 lines. The ratio of 18:1 to 18:2 was tightly interrelated as the same QTL were associated with the concentrations of 18:1 and 18:2. A quantitative trait locus that explained 63% of the phenotypic variation in the ratio of 18:1 to 18:2 is tightly linked to umc65 on chromosome 6 in the region of the linoleic acid1 locus.

Mapping the anther culture response genes in maize (Zea mays L.).

In order to map the genes conditioning the induction of embryos during our anther culture process, we evaluated F2 plants from three different crosses for their anther culture ability and also performed RFLP analysis on these plants. The results showed that six chromosomal regions appear to be associated with the ability to induce embryo-like structures from maize microspores. These regions are located on chromosomes 1 (two regions), 3, 5, 7, and 8. Some of these chromosomes are identical to those found in previous studies and we have localized the regions more precisely. Notably, all chromosome regions identified, except one, are near viviparous mutant loci. Since the viviparous mutations are known to involve the plant hormone abscisic acid (ABA), these results suggest that ABA or its antagonist, gibberellic acid (GA3), might somehow be related to anther culture ability. We also propose some combinations of probes to screen for anther culture ability in the three genotypes studied.

RFLP mapping of the sugary enhancer1 gene in maize.

RFLP marker data from an F2∶3 population derived from a cross between a sugary1 (su1) and a sugary enhancer1 (su1, sel) inbred were used to construct a genetic linkage map of maize. This map includes 93 segregating marker loci distributed throughout the maize genome, providing a saturated linkage map that is suitable for linkage analysis with quantitative trait loci (QTL). This population, which has been immortalized in the form of sibbed F2∶3 families, was derived from each of the 214 F2 plants and along with probe data are available to the scientific community. QTL analysis for kernel sucrose (the primary form of sugar) concentration at 20 days after pollination (DAP) uncovered the segregation of seven major QTL influencing sucrose concentration; a locus linked to umc36a described the greatest proportion of the variation (24.7%). Since maltose concentration has previously been reported to be associated with the se1 phenotype, an analysis of probe associations with maltose concentration at 40 DAP was also conducted. The highly significant association of umc36a with maltose and sucrose concentrations provided evidence that this probe is linked to se1. Phenotypic evaluation for the se1 genotype in each F2∶3 family enabled us to map the gene 12.1 cM distal to umc36a. In contrast to previous work where se1 was reported to be located on chromosome four, our data strongly suggest that the sugary enhancer1 locus maps on the the distal portion of the long arm of chromosome 2 in the maize genome.

Interaction of nuclear and mitochondrial genomes in the alteration of maize mitochondrial orf221 transcripts.

The interaction of nuclear and mitochondrial genomes in the alteration of maize (Zea mays L.) mitochondrial orf221 transcript patterns was examined. Northern analyses involving specific maize nuclear genotypes associated with N, C or S cytoplasms revealed considerable orf221 transcript heterogeneity. F1 progenies were developed from maize inbred-cytoplasm combinations that differed for orf221 transcript patterns. Northern analyses revealed that the presence or level of abundance of certain orf221 transcripts was dependent on nuclear genotype. The maize inbred B37(C) exhibits orf221 transcripts of 3500, 3200, 2800, and 1300 nt whereas the F1 of B37(C) x Ky21(N) does not exhibit a 2800-nt transcript but does give transcripts of 2100 and 1250 nt in addition to 3500-, 3200- and 1300-nt transcripts. Northern analyses also suggested that the size or the presence of certain orf221 transcripts was related to the mitochondrial genome configuration. Maize inbred A619 exhibits a 2300-nt orf221 transcript when associated with N cytoplasm and a 2100-nt orf221 transcript when associated with C and S cytoplasms. As a result of deletion of the gene T-urf13, the A188(T7) mitochondrial mutant exhibits only a 3100-nt orf221 transcript and not the very complex T-urf13/orf221 transcript pattern associated with A188(T). The genetic stock A188(T7) x W64A(N)(2) gives a highly abundant 2100-nt orf221 transcript not detected in A188(T7). Deletion of T-urf13 has enabled the nuclear genotype of W64A(N) to alter orf221 transcript patterns in a manner not detected in T cytoplasm. This observation suggests that alteration of the mitochondrial genomic configuration adjacent to orf221 results in a different response to nuclear gene products from that observed when or2f21 is present in the T mitochondrial genome configuration.

Change in ribosomal DNA intergenic spacer-length composition in maize recurrent selection populations. 1. Analysis of BS13, BSSS, and BSCB1.

Five different ribosomal DNA (rDNA) intergenic spacer-length variants (slvs) were detected among the maize inbreds which were the progenitors of Iowa Stiff Stalk Synthetic (BSSS). One rDNASstI restriction site polymorphism in the 3' region of the 26S gene was detected. Nine different rDNA intergenic spacer (IGS) hybridization fragment patterns (assigned letter designations A-I) were observed among the BSSS progenitors. Following 7 cycles of half-sib recurrent selection in BSSS using the Ia13 double cross as a tester, hybridization fragment pattern E became predominant in the population. In contrast, 11 cycles of reciprocal recurrent selection in BSSS with the Iowa Corn Borer Synthetic No. 1 (BSCB1) population resulted in hybridization pattern D becoming predominant. Hybridization pattern E is present in the elite inbreds B14, B37, B73, and B84, which were derived from different cycles of the BSSS half-sib recurrent selection program with Ia13. Hybridization pattern D is present in the elite inbreds B89 and B94, which were derived from different cycles of the BSSS reciprocal recurrent selection program with BSCB1. Therefore, two different forms of recurrent selection on BSSS resulted in different hybridization patterns becoming predominant in the selected populations and present in elite inbreds derived from the populations. These results also suggest that rDNA IGS hybridization fragment patterns D and E, which both have the longest slv detected, may have a selective or adaptive advantage in BSSS materials grown in the Corn Belt.