bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapeseed Mutants with Reduced Levels of Polyunsaturated Fatty Acids and Increased Levels of Oleic Acid
Authors: Auld Dick L. , Heikkinen Mary K. , Erickson Donna A. , Sernyk John L. , Romero Juan E.
Published: July 2010

Development of cultivars of both tetraploid (Brassica napus L.) and diploid (B. rapa L.) rapeseed with reduced levels of polyunsaturated fatty acids and increased levels of oleic acid could increase both the utility and value of the oil. The objective of this experiment was to use chemcical mutagenesis to induce mutations for these traits in rapeseed. Imbibed seed of ‘R‐500’ (B. rapa) and ‘Cascade’ (B. napus) were treated with 5% v/v of ethyl methanesulfonate. The M2 generations of these populations were screened to identify mutants with low levels of polyunsaturated fatty acids (PUFA) using a modified thiobarbituric acid procedure. Putative mutants and their derived progeny were increased in the greenhouse and the seed analyzed for fatty acid composition using gas chromatography. The most promising mutant identified from 4 734 M2 seeds of B. rapa, was M‐30, which had 2.1% linoleic acid and 3.0% linolenic acid, vs. 11.9% linoleic and 8.6% linolenic acid in the original cultivar. This mutant was crossed with ‘Tobin’ to derive F4 lines having <6% total PUFA and oleic acid concentrations >87%. The most promising mutant identified from 39 504 M2 seeds of B. napus was X‐82, which had 6.6% PUFA, vs. 27.4% PUFA in Cascade. Several M3 and M4 lines derived from X‐82 had <6% total PUFA and >88% oleic acid. The development of commercial cultivars with reduced levels of polunsaturated fatty acid in both B. rapa and B. napus could develop new markets for both industrial rapeseed and edible canola oil.
Comparison of Methods for Identifying Populations for Genetic Improvement of Maize Hybrids
Authors: Pfarr David G. , Lamkey Kendall R.
Published: July 2010

The ability to effectively use population identification methods to improve elite single crosses would allow breeders to concentrate resources on populations known to carry new favorable alleles, thus enhancing breeding success. The value of a population for improvement of a single cross is determined by the relative number of dominant alleles contained in the population at loci that are homozygous recessive in the single cross (Class ℯ loci). This study was conducted to compare population identification methods for their ability to rank maize (Zea mays L.) populations for number of dominant alleles at Class ℯ loci. The methods were evaluated by using populations of known genetic composition. The methods evaluated included, ′, upper bound (UBND), testcrossing to a single cross (TCSC), testcrossing to an inbred line, and performance per se. Estimates provided by′ and UBND had the largest correlations with the genetic structure of the populations for grain yield, ear height, and silking date. Rank correlation coefficients between estimates of ′ and UBND pooled across single crosses were 0.98 for grain yield, 0.99 for ear height, and 0.99 for silking date. The pooled rank correlation coefficients between′ and percentage favorable parent were negative for grain yield and silking date. Pooled rank correlations between and′ and between and UBND also were negative. In some instances, the population expected to be most favorable was identified by testcrosses to an inbred parent of the single cross. Per se performance of the populations was not correlated with the percentage favorable parent. The′ and UBND statistics were equally effective for identifying populations with the greatest frequency of dominant alleles at Class ℯ loci.
Testing for Linkage between the Rxp Locus and Nine Isozyme Loci in Soybean
Authors: Palmer Reid G. , Lim Sung M. , Hedges Bradley R.
Published: July 2010

Chromosome mapping studies are needed in soybean [Glycine max (L.) Merr.] to identify the 20 linkage groups. The objective of this research was to identify isozyme loci linked to the Rxp locus. Bacterial pustule of soybean is caused by Xanthomonas campestris pv. glycines. Soybean lines homozygous for the rxp allele are resistant, while the Rxp allele conditions susceptibility to the bacterial disease. Nine isozyme loci were tested for linkage to the Rxp locus. Starch gel electrophoresis analysis was used to assay for the isozymes. The Linkage‐1 computer program was used to estimate recombination distances. On the basis of 650 F2 plants from reciprocal crosses of ‘Clark 63’ × PI 437477B, a percentage recombination estimate of 15.18 ± 3.81 was obtained with the Rxp locus and a malate dehydrogenase variant. This represents a new linkage group (Linkage Group 20) in soybean. All other linkage tests gave independent assortment.
Inheritance of Resistance of Three Russian Triticale Lines to the Russian Wheat Aphid
Authors: Nkongolo Kabwe K. , Quick James S. , Peairs Frank B.
Published: July 2010

Knowledge of inheritance of resistance to major diseases and pests is important to plant breeders. This study was conducted to determine the inheritance of resistance to the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in three winter triticale (× Triticosecale Wittmack) lines that have been found to be outstanding sources of RWA resistance. The three resistant lines (PI 386148, PI 386149, and PI 386156) were intercrossed and crossed with three susceptible triticale cultivars (TX33000, NE83T12, and Lasko). The parents, F1, F2, and backcross populations were artificially infested with RWA in greenhouse tests. The data indicate that resistance to RWA is controlled by a single dominant gene in each line. The lack of segregation for susceptibility in F2 progenies from the resistant × resistant crosses indicates a high probability that the resistance genes in these lines are at a common locus. Gene symbols for these resistance genes will be assigned when the allelic relationships with other RWA resistance genes identified in wheat and triticale are determined.
Gibberellins and Heterosis in Sorghum
Authors: Rood Stewart B. , Witbeck J. E. Teddy , Major David J. , Miller Fred R.
Published: July 2010

Two triplet combinatioas of sorghum, [Sorghum bicolor (L.) Moench], each consisting of two homozygous parental lines and their F1 hybrid (ATx623 × Hegaria; ATx378 × RTx430), were grown in controlled environment chambers to examine the possible relationship between gibberellins (GAs) and heterosis (hybrid vigor). Heterosis for shoot growth occurred as shoot dry weights and leaf areas were greater in the hybrids than in parental inbreds. The exogenous application of 0.1, 0.5, or 1.0 mg GA3 by pipetting into the leaf whorl promoted leaf sheath and leaf blade elongation in all genotypes. GA3 also promoted shoot dry weight and/or leaf area in three of the four inbreds, but hybrids were relatively unaffected. Endogenous GA1 was measured by gas chromatography‐selected ion monitoring, using [2H2]GA1 as an internal standard. At one of the two harvests (Day 22 and 29) for each triplet, the hybrid contained significantly higher concentrations of GA1 than either parent. Endogenous GA3 was characterized by GC‐SIM in samples, from the second harvest and showed the same pattern as GA1. Thus, at some stages, these sorghum inbreds apparently have a partial deficiency of endogenous GA. The response to exogenous GA3 application suggests that the GA deficiency is a limitation to their growth. Thus, GAs are apparently involved in heterosis for shoot growth in sorghum.
Growth Regulator Effects on Aboveground Dry Matter Partitioning during Grain Fill of Spring Barley
Authors: Ma B. L. , Smith Donald L.
Published: July 2010

It is not clear whether alteration in grain yield due to application of plant growth regulators (PGRs) to cereal crops is caused by altered dry matter accumulation, changes in partitioning of dry matter into grain, or both. A 3‐yr field study was conducted using two widely grown spring barley (Hordeum vulgare L.) cultivars, Cadette and Leger, to evaluate the effects of chlormequat (CCC) (2‐chloroethyl‐N,N,N‐ trimethylammonium chloride) or ethephon (2‐chloroethyl phosphonic acid) on dry matter production and partitioning among plant parts during grain fill. The growth regulators were applied at three stages of crop development. The experiments were conducted on Bearbrook clay soil (fine, mixed, nonacid, Mesic Humaquept) at McGill University, Canada, from 1987 to 1989. Treatments consisted of application of CCC (1.2 kg a.i. ha−1) or ethephon (0.48 kg a.i. ha−1) at Zadoks growth stage (ZGS) 13, 30 and 39. Ethephon application at ZGS enhanced dry matter accumulation in the nongrain plant parts (chaff, culms, leaf blades, and leaf sheaths) in both 1988 and 1989, and decreased grain mass per spike (number of grains per spike and 1000‐ grain weight) in 1989. This resulted in a yield reduction in that year. In 1988, an increased grain mass per spike with ethephon resulted in improved grain yield. For Cadette, CCC treatment also increased dry matter accumulation in leaf blades, leaf sheaths, and chaff in 1988. Grain yield per square meter was also increased by a ZGS‐13 application in that year. In general, this work revealed that PGR application does not increase total dry matter accumulation on a per‐shoot basis, but does affect dry matter partitioning patterns, leading to alterations in grain yield that may be positive or negative depending on the conditions during a given crop year.
Adaptation to Midseason Drought of Cowpea Genotypes with Contrasting Senescene Traits
Authors: Gwathmey C. Owen , Hall Anthony E.
Published: July 2010

Monocarpic senescence traits may influence adaptation to midseason drought by their effects on drought escape and dehydration avoidance. Adaptive attributes of two related cowpea [Vigna unguiculata (L.) Walp.] genotypes, contrasting in monocarpic leaf senescence, were evaluated under well‐watered and drought treatments in the field. Drought stress was imposed during flowering and pod filling for 19 consecutive days before irrigation was resumed. Delayed leaf senescence was expressed by genotype 8517 under both water regimes. Drought and monocarpic senescence concurrently reduced leaf area in both genotypes, but 8517 maintained greater leaf area and plant viability under either water regime than did the senescent cultivar, CB5. Both genotypes showed similar 13C discrimination under complete irrigation but 8517 discriminated significantly less against 13C than did CB5 under drought stress. Based on discrimination data, transpirational water‐use efficiency of droughted 8517 was estimated to be 10 to 14% higher than that of CB5. Plant survival was not significantly affected by the drought treatment, but a higher percentage of 8517 than CB5 plants survived the first podset and subsequently produced a large second podset. Total seed yields did not differ significantly between genotypes, but seasonal yield distribution differed markedly. Total reproductive duration of drought‐stressed 8517 was 50% greater than that of CB5, and 60% of its pod production escaped the drought. The delayed leaf senescence traits may enhance adaptation of cowpea to semiarid zones by improving the capacity to survive and recover from midseason drought.
Evaluation of the Afila‐Tendriled Acacia (afaf‐tactac) Pea Foliage Type under Minimal Competition
Authors: Goldman Irwin L. , Gritton Earl T. , Flannery Patrick J.
Published: July 2010

The afila (of) gene replaces pea (Pisum sativum L.) leaflets with tendrils, and the tendriled‐acacia (tac) gene restores small leaflets to the tendrils of af plants. The agronomic performance of plants homozygous for both af and lac has not been studied. A near‐isogenic set of three foliage types: normal (AfAf‐TacTac), semi‐leafless (afaf‐ TacTac), and afila‐tendriled acacia (afaf‐tactac) in three genetic backgrounds was evaluated for 2 yr in two locations using a normal plant population for pea grown for processing. The objective of the study was to measure performance of afaf‐tactac in comparison with afaf‐TacTac and AfAf‐TacTac at high levels of interplant competition. At the green pea harvest stage, the total foliage area of afaf‐tactac plants was 10% greater than for afaf‐TacTac, but not significantly different from AfAf‐TacTac. Yield of afaf‐tactac averaged 29% lower than AfAf‐TacTac and 26% lower than afaf‐TacTac in the early and midseason genetic backgrounds, but did not differ significantly in the late genetic background. Significant increases in vine length, number of nodes, lowest pod‐bearing node, and first node with nonsenescent foliage were measured in afaf‐tactac over AfAf‐TacTac and afaf‐TacTac in the early and midseason genetic backgrounds. The addition of leaflets to the tendrils of a/a/plants through incorporation of the tac gene did not result in green pea yield improvement of plants grown at a standard highly competitive population density.
Zein Diversity in Reid, Lancaster, and Illinois Chemical Corn Strains Revealed by Isoelectric Focusing
Authors: Wilson Curtis M.
Published: July 2010

Zeins, the major storage proteins in corn (Zea mays L.) endosperms, consist of a large number of related polypeptides. At least 41 different AB‐(a) zeins, detected by isoelectric focusing, have previously been found in Corn Belt inbreds. This study examines the variability of zeins in ‘Reid Yellow Dent’, ‘Lancaster Sure Crop’, and eight lllinois chemical strains. Individual seeds of Reid and Lancaster contained 8 to 16 bands each. Segregation occurred for most zeins, with totals of 26 and 25 bands, respectively, in the two open‐pollinated varieties. However, every zein band had been found in a previously studied inbred. Isoelectric focusing of zein also revealed that variation still exists in the lllinois chemical strains, even after 82 generations of selection. Each strain contained 8 to 15 identifiable zein proteins, with 2 to 8 showing segregation within a strain. The reverse high‐oil strain showed segregation for 8 of 13 zeins, whereas the reverse low‐oil and reverse high‐protein strains showed segregation for only 2 zeins. When the results from all eight chemical strains were totaled (partially representing the original Burr's White open‐pollinated variety), there was nearly as much zein variation as in Reid and Lancaster.
Inheritance of Partial Resistance to White Mold in Inbred Populations of Dry Bean
Authors: Miklas Phillip N. , Grafton Kenneth F.
Published: July 2010

Improving partial resistance to the fungus Sclerotinia sclerotiorum (Lib.) de Bary, the causal organism of white mold disease, is a major goal of many dry bean (Phaseolus vulgaris L.) breeding programs. Our objective was to determine if selection for partial physiological resistance (PPR) or partial field resistance (PFR) among inbred lines would have potential for increasing resistance in dry bean. Three populations of F2:4 lines that originated from two hybridizations of snap and pinto bean, NY 5262 ✕ ‘Topaz’ and NY 5262 ✕ CO81‐12034, and one between navy bean, ‘Bunsi’ ✕ D76125, were tested across two greenhouse and field environments for inheritance of PPR and PFR, respectively, to white mold disease. Each population consisted of ⊄50 F2:4 lines. The PPR trait was indicated by lesion length (LL) measured on inoculated excised stems obtained from 28‐d‐old plants (28‐d assay), and PFR was evaluated in field trials with a disease incidence index (DII). Means for LL and DII, combined across 28‐d assays and field environments, were normally distributed (P > 0.01), indicating that no discrete segregation classes occurred. Transgressive segregation was observed for both LL and DII for each population. Estimates of genetic variance (σ2g) for LL in two populations and DII in each population were significant (>2 SE). Heritability estimates for LL (0.27, 0.38, and 0.66) were lower than DII (0.77, 0.58, and 0.70) for each population. Low genetic correlations between LL and DII (0.37**, 0.16, and 0.05) for each population suggested that selection for both traits is warranted. The significant estimate for σ2g, and high estimates for heritability and expected genetic gain for reduced LL and DII, indicated that progress from selection among inbred lines of dry bean for improved partial resistance to white mold could be made.
Inheritance of Resistance to Race 4 of Sunflower Downy Mildew in Wild Sunflower Accessions
Authors: Tan Ahmet S. , Jan Chao‐Chien , Gulya Thomas J.
Published: July 2010

Race 4 of sunflower downy mildew (SDM), Plasmopara haistedii (Farl.) Beri. & De Toni in Sacc. was identified in 1985, and currently is prevalent worldwide. Our objectives were to (i) determine the mode of inheritance of resistance to Race 4 (SDM‐4) of P. halstedii in wild Helianthus annuus L. accessions PI 413047, PI 413131, PI 413157, and PI 413161, and (ii) study allelic relations of resistance genes these accessions and SDM‐4 resistance in line HA 336. Seedlings were classed as resistant (R) or susceptible (S) based on detection of pathogen on cotyledonary or true leaves. Resistant plants from the wild accessions and HA 336 were crossed with susceptible lines HA 89 and cytoplasmic male‐sterile (cms) HA 89. Most F1 progenies of wild accessions/HA 89 and cms HA 89/segregated 1R:IS, suggesting that most of the plants selected from wild accessions were heteruzygous for a single dominant gene for resistance to SDM‐4. Sogregation ratios of 1R:IS in backcross families confirmed that SDM‐4 resistance was inherited as a single dominant gene. Resistant segregates of halfdiallei crosses among resistant F1 plants from different sources were crossed with HA 89 and cms HA 89. Segregation ratios indicated that different resistance genes occur in PI 413047, PI 413131, PI 413157, and PI 413161, and that these genes differ from PP in HA 336. The four genes found in these wild accessions provide unique sources of resistance to the pathogen and, with introgression into cultivated sunflower (H. annuus L.), should reduce genetic vulnerability to this disease.
Chromosome 3D Influences Photosystem II Quantum Efficiency in Winter Wheat
Authors: Bobo Marie‐Sylvie , Planchon Claude , Morris Rosalind
Published: July 2010

The photosynthetic efficiency of leaves under low light is considered to be a major determinant of crop photosynthetic performance. The aim of this study was to identify chromosome effects on some parameters associated with photosynthetic efficiency under low light. Photosynthetic activity was analyzed using a pulse.amplitude modulation fluorometer for the measurement of the photochemical quenching (Qp) and of the quantum efficiency of Photosystem II electron transport (ΦPSU) under an actinic light of 45 μmol m−2s−1 on wheat (Triticum aestivum L.) plants grown in pots under natural conditions. Reciprocal sets of chromosome substitution lines between the hard red winter wheat cultivars Wichita and Cheyenne were used to identify the chromosomes involved in the expression of these traits. The two parental cultivars were significantly different for Qp and ΦPSU Chromosome 3D affected ΦPSU at various stages of development when plants were exposed to low light intensities. Relationships between yield and photosynthetic efficiency under non saturating light have been postulated. Thus, chromosome 3D probably influences bread wheat productivity.
Genetic Linkage Tests for the Rj4 Gene in Soybean
Authors: Devine Thomas E.
Published: July 2010

The Rj4 allele in soybean, Glycine max (L.) Merr., conditions an ineffective nodulation response primarily with bradyrhizobial strains classified as Bradyrhizobium elkanii, which are less efficient in N2 fixation with soybean, thus protecting the plant from many of these strains. The diminishing frequency of the RJ4 allele with agronomic selection poses the question of possible linkage with genes of negative agronomic selective value. Little is known of the linkage relationships of the Rj4 locus. This report analyzes genetic linkage tests of the Kj4 locus with 12 other loci: F, Frl, Fr2,1, LI, Ln, P, Wl, Y9, Y10, Y12, and YJ7. Segregating F2 and F3, progeny of several crosses were used to generate data for analysis. The Rj4 assays were conducted by planting seeds in sterile vermiculite and inoculating with broth cultures of strain USDA 61 from the Beltsville Rhizobium Culture Collection and examining the roots after 2 to 4 wk culture in the greenhouse. Other traits were scored either in the field or in the greenhouse. Chisquare was used to test for linkage, and the product method or method of maximum likelihood was used to estimate recombination. Only the Y17 locus showed evidence of genetic linkage with Rj4. The estimated recombination of Y17 and Rj4 was 46 ± 2%.
Phenotypic Recurrent Selection for Modified Reproductive Period in Soybean
Authors: Hanson W. D.
Published: July 2010

Seed‐filling duration has generally shown a positive association with seed yield in soybean [Glyelne max (L.) Merr.], but results have been inconsistent among studies. Four phenoWpic recurrent selection programs were completed, increased flowering.period duration (FPD) vs. increased seed‐filling duration (SFD) and long vs. short reproductive period duration (RPD), with the objective of investigating the effects of these modifications on seed development and seed yield. Selection for average physiological maturity (RT) maintained R7 maturities among populations. Selection for increased RPD through FPD or SFD increased genetic correlations between reproductive stages. The major responses to selection occurred in the first cycle due in part to the 3‐yr evaluation, but high correlations between stages also restricted progress. Manipulating RPD modified primarily FPD. The SFD seemed to have a minimum threshold, but responded to selection pressure. Divergent selection for RPD created a 10‐d difference in RPD, but the selection had minimal effects on seed yield potential. The soybean has the capacity to achieve seed yield independent of changes in duration of reproductive stage. Increasing RID through increased SFD within a broad‐base population had an associated increase in seed set and in seed yield for a set of favorable environments, but this yield advantage was not expressed for a set of environments with drought stress during the reproductive period. Increased SFD was associated with increasing potential number of seed set and, as has been shown, decreasing assimilate uptake rate. Selection for increased SFD would be important for populations where SFD could be limiting. The effects of modifying seed‐filling duration are not clear‐cut, but manipulating facets that affect it can create unacceptable responses.
Leaf Gas Exchange in Water‐Stressed Common Bean and Tepary Bean
Authors: Castonguay Yves , Markhart Albert H.
Published: July 2010

Tepary bean, Phaseolus acutifolius A. Gray var. latifolius G. Freeman, is adapted to hot arid conditions and might be a valuable source of genes to improve the drought tolerance of P. vulgaris L. We tested the hypothesis that P. acutifolius adaptation to arid environments relies on differences in gas exchange characteristics leading to greater water‐use efficiency. Both species were subjected to controlled levels of water stress by enclosing the root systems in semipermeable membranes immersed in nutrient solutions osmotically adjusted with polyethylene glycol. Phaseolus acutifolius had higher net photosynthetic rates (Pn) than P. vulgaris at high to moderately low water potentials. The Pn rates of P. acutifolius declined more rapidly with lower water potential than those of P. vulgaris. This response was related to increased stomatal closure with decreased water potential. Higher Pn, rates at any given internal CO2 partial pressure (C1) led to higher water‐use efficiency in P. acutifolius than in P. vulgaris. Analysis of the initial slope of Pn vs. C1, curves indicated that P. acutifolius bad higher carboxylation efficiency (CE) at low C1. In both species, water stress significantly reduced light‐ and CO2‐saturated Pn rates and only slightly lowered the CE. Similar mesophyll palisade surface area in P. acutifolius and P. vulgaris suggested that differences in Pn rates at low C1 might be related to biochemical rather than anatomical leaf characteristics. Higher water‐use efficiency at moderate water deficits may contribute to P. acutifolius adaptation to arid environments.
Mycorrhizal Effects on Interspecific Plant Competition and Nitrogen Transfer in Legume‐Grass Mixtures
Authors: Hamel Chantal , Furlan Valentin , Smith Donald L.
Published: July 2010

Mycorrhizal fungi may play a role in the interactions between components of legume‐grass mixed swards by their enhancing effect on plant P uptake and on legume N2‐fixation rate. The effects of mycorrhizal fungi on interspecific plant interactions and N transfer from legume to grass were studied in two legume‐grass forage mixtures grown under three P fertilization regimes. In two experiments, one involving an alfalfa‐bromegrass (Medicago sativa L.‐Bromus inermis Leyss.) mixture and the other, an alfalfa‐timothy (Phleum pratense L.) mixture, plants were inoculated or not with Glomus intraradix and fertilized with 0, 14.2 or 28 kg P ha−1. Phosphorus fertilization sometimes increased plant tissue P concentration, especially in timothy, but it never affected grass/legume biomass ratios. The effects of the mycorrhizal fungus were seasonal and were most evident in the August harvests, when mycorrhizal inoculation increased the yield of alfalfa at the expense of bromegrass or timothy, reducing the grass/legume dry mass ratio in both mixtures. Transfer of 15N from legume to grass was demonstrated, but this transfer was not enhanced by mycorrhizal colonization of plants. Mycorrhizal colonization increased P accumulation in the alfalfa components of the mixtures (33% with bromegrass and 17% with timothy); however, P concentrations in the legume biomass were above the P sufficiency level in nonmycorrhizal plants and were not increased by mycorrhizal colonization. Therefore, the seasonal increase in alfalfa yield at the expense of the grass was apparently not caused by enhancement of P uptake by mycorrhizal colonization. Diagnosis and Recommendation Integrated System (DRIS) indices calculated from a complete nutrient analysis of the tissue revealed that the beneficial effect of mycorrhiza on alfalfa production was associated with a better nutrient balance (mainly Ca and Mg) of the plants.
Growth of C3 and C4 Perennial Grasses under Reduced Irradiance
Authors: Kephart Kevin D. , Buxton Dwayne R. , Taylor S. Elwynn
Published: July 2010

Several studies have compared C3 and C4 species for response to water and temperature regimes. Little comparative information exists, however, on growth responses of C3 and C4 species to irradiance regime. The objective of this study was to determine adaptive responses of C3 and C4 grasses to irradiance regime. Three C3 and two C4 perennial forage grasses were field—established near Ames, IA, and grown under 37, 70, and 100% of full sunlight by use of polypropylene shade cloths. Morphology and growth measurements were conducted three times at ⊄21‐d intervals each year for 2 yr. Net leaf CO2 exchange rate (CER) was measured for one C3, and one C4 grass. Specific leaf weight increased and leaf‐area ratio decreased with increasing irradiance similarly in all five species. Responses of herbage yield, shoot dry weight, and crop growth rate to irradiance were two to three times greater for C4 grasses than for C3 grasses. Responses of CER to irradiance were greater for the C4 grass than for the C3 grass. Morphological adaptive responses were similar for C3 and C4 grasses, but responses closely related to photosynthesis (e.g., CER, growth rate, and herbage yield) were affected more in C4 than in C3 species.
Forage Quality and Morphological Components of Diverse Clovers during Primary Spring Growth
Authors: Brink Geoffrey E. , Fairbrother Timothy E.
Published: July 2010

Forage quality of dover (Trifolium spp.) may be influenced by changes in nutrient concentration of morphological fraction as a function of growth habit or life cycle. We compared the dry matter (DM) accumulation trends of four clovers differing in growth habit and life cycle, and determined the influence of plant fraction nutritive value on total forage quality. Primary spring growth of berseem (T. alexandrinum L.), red (T. pratense L.), subterranean (T. subterraneum L.), and white (T. repens L.) clovers was harvested in each of 2 yr beginning in late March, and thereafter every 10 d (eight harvests total). Digestible dry matter (DDM) and crude protein (CP) concentration determined for leaf, petiole, stem, and reproductive fractions, and total forage of each species at each harvest. Total DM accumulation of berseem and red clover increased linearly to a maximum of 547 and 407 g DM m−2, respectively, by Day 61, while that of subterranean and white clover increased nonlinearly to a maximum of 336 and 219 g DM m−2, respectively, by Day 51. Days to maximum accumulation of stem DM in erect species and petiole DM in prostrate species corresponded with maximum total DM accumulation in the respective species. Leaf‐to‐stem weight ratio ranged from 0.27 to 1.42 for berseem clover and from 1.10 to 3.04 for white clover, although quadratic trends for leaf DM accumulation for the two species were similar. Mean DDM of berseem and red clover forage declined 2.0 g kg−1 d−1. Based on trends for dry matter accumulation and nutrient concentration of the leaf fraction, subterranean and white clover merit consideration equal to berseem and red clover as pasture legumes.
Development and Application of RFLPs in Polyploids
Authors: Sorrells Mark E.
Published: July 2010

Mapping and application of restriction fragment length polymorphisms (RFLPs) in polyploids has lagged behind diploids due to complications from (i) a large number of segregating genotypes, (ii) comigration of fragments, (iii) poorly characterized genome constitution nod/or chromosome pairing behavior, and (iv) complicated genotype characterization due to multiple fragments. Strategies that facilitate mapping in polyploids include linkage maps for diploid relatives, aneuploid stocks, and haploid or doubled haploid populations; however, each approach has advantages and disadvantages for different species. This review relates primarily to those polyploids with regular bivalent pairing, since multivalent pairing can result in double reduction and aneuploidy, further complicating linkage analysis. The use of single‐dose restriction fragments for segregation and linkage analyses can greatly reduce the complexity of mapping in polyploids. Because of the large difference between disomic and polysomic polyploids in detection of repulsion phase linkage, a comparison of the number of coupling‐ and repulsion‐phase linkages will provide an indication of the degree of preferential pairing among chromosomes in each linkage group. When diploid relatives are used for mapping, probe library survey filters must contain a lane for each species being mapped, clones must be polymorphic for parents of each species mapping population, new fragments with a different molecular weight may map to different locations in the polyploid because of structural rearrangements, genomes must be relatively homosequential or rearrangements well characterized, and the diploid population should exhibit a high level of polymorphism. Aneuploid or deficiency genetic stocks can be efficiently employed for mapping fragments for species exhibiting moderate to low polymorphism, because nearly every fragment hybridizing to a probe is assigned to a chromosome or subchromosomal location. This approach does not depend on regular meiosis in a hybrid, thus avoiding the problem of chromosomal rearrangements, abnormal pairing, and sterility in wide crosses. Where aneuploids are not available, markers can be used to advantage in developing such genetic stocks. Inbred populations have significant advantages for mapping because of the reproducibility of the genotypes and the absence of heterozygotes. Exotic genotypes and alien germplasm are prime sources of novel alleles for economically important traits. In the future, the breeder will be able to cross different genotypes that are known to possess positive alleles at different loci and, using markers for those alleles, select transgressive segregates. With this technology, breeders will likely incorporate many novel alleles for agronomic traits from alien species into elite cultivars.
Persistence of Alfalfa under Continuous Grazing in Pure Stands and in Mixtures with Tall Fescue
Authors: Smith S. Ray , Bouton Joseph H. , Hoveland Carl S.
Published: July 2010

Some alfalfa (Medicago sativa L.) germplasms and cultivars have shown long‐term persistence under continuous grazing in pure stands in the southeastern USA, but interspecies competition with tall fescue (Festuca arundinacea Schreber) may result in stand declines. We tested the persistence and forage productivity of alfalfa cultivars and a germplasm that differed in grazing tolerance under continuous grazing in pure and mixed stands with tall rescue. All stands were subjected to severe, continuous grazing by beef cattle (Bos taurus or cross bred) for ≈20 wk in each of 3 yr on a Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult). After 3 yr of continuous grazing, GAWCG, Alfagraze, Spredor II, and Apollo had 57, 41, 5 and 4 plants m−2 in pure stands and 17, 9, 0, and 1 in mixed stands, respectively. Total forage production, spring hay yields, and regrowth under exclosures (cattle excluded) did not differ for pure and mixed stands the first season, but the Alfagraze–tall rescue mixture had the highest production the second season. Alfalfa composition of mixed stands of Alfagraze and GA‐WCG averaged 71% during the first growing season, 32% during the second, and 27% at the beginning of the third grazing season, while Apollo and Spredor II composition averaged 62, I0, and 1% for the same periods. Alfagraze and GA‐WCG maintained higher levels of root carbohydrates during continuous grazing than Apollo and Spredor II during the first grazing season. Alfalfa tolerant to grazing in pure stands also had superior persistence under severe, continuous grazing in mixed stands with tall fescue.
Corn Grain Density Characterized by Two Specific Gravity Techniques
Authors: Bergquist Richard R. , Thompson Donald L.
Published: July 2010

Grain quality of corn (Zea mays L.) is an important breeding consideration, hindered by the limitations of visual selection. This exploratory laboratory study sought to develop preliminary information on two simple techniques for estimating kernel density, which is assumed to relate to grain hardness. The two are the floater technique (percentage of floating kernels in a salt solution) and the conventional technique (specific gravity as related to water). Kernel density increased with selection for low percentage floaters during early inbreeding. Narrow‐sense heritability of percentage floaters was 0.73. Density of F1 seed was closely related to that of the female parent; e.g., 19 crosses averaged 32.8% floaters and the 19 female parents as inbreds averaged 31.2% floaters, whereas the reciprocal crosses averaged 97.6% floaters and the common female parent averaged 99.8% floaters. Flat kernels averaged 31.6% floaters and round kernels averaged 43.0% in one experiment, and averaged 12.4 and 24.7% floaters, respectively, in another. Density of three grade sizes varied relative to genotype. A test solution of specific gravity 1.275 was satisfactory for general evaluation, but higher levels were useful for additional determinations. The two techniques were correlated at about −0.8 (P < 0.01)
Interactions between Carbon Dioxide and Water Deficits Affecting Canopy Photosynthesis: Simulation and Testing
Authors: Grant Robert F.
Published: July 2010

Increases in atmospheric CO2 concentrations (Ca) are likely to increase CO2 fixation and reduce transpiration by crop canopies. Mathematical modeling of the processes controlling gas exchange may be used to estimate the extent to which exchange is likely to be altered by Ca under site‐specific conditions. A simulation model was constructed from fundamental equations for CO2 fixation, transpiration and energy exchange in order to estimate canopy gas exchange under different Ca. The model was then tested with data from a growth chamber study. The model reproduced an increase in net photosynthesis from 35 to 65 μmol m−2 s−1, and a decrease in transpiration from 14 000 to 11 000 μmol m−2 s−1, for an irrigated soybean [Glycine max (L.) Merr.] canopy when Ca was increased from 330 to 800 μmol mol−1. The consequent increase in water use efficiency from 2.7 to 5.5 mmol mol−1 was confirmed from the growth chamber study. In the model, this increase was governed by changes in the partitioning of latent and sensible components of the crop energy balance arising from changes in canopy stomatal resistance. Changes in the ratios of latent and sensible heat fluxes simulated by the model at Ca = 800 vs. 330 μmol mol−1 caused simulated increases in canopy temperatures of ≈ 1.0 °C, similar to recorded increases in other studies. There is evidence from model output that changes in canopy CO2 fixation caused by Ca may be reduced in water stressed canopies. However, our understanding of water deficit effects on photosynthesis remains largely empirical, so that estimates of canopy gas exchange under combined water deficits and changed Ca remain speculative. There is a need to extend experimental studies of Ca effects on photosynthesis and transpiration to include studies under water stress in order to test model hypotheses.
Relative Fiber Uniformity between Parent and F1 and F2 Generations in Cotton
Authors: Dever Jane K. , Gannaway John R.
Published: July 2010

Hybrids (F2) of cotton (Gossypium hirsutum L.) reportedly offer improved seedling vigor, disease tolerance, and yield for this major crop of the Texas High Plains but raise concern about increased fiber property variability. Our objective was to compare fiber variability in the F2 generation with that in pure lines and in F1 hybrid cultivars. A four‐parent complete diallel mating system using lines with similar and divergent fiber types resulted in 28 treatments: 4 parents, 12 F1 hybrids, and 12 F2 hybrids. The variance (converted to base 10 logarithm) of 10 plants in each treatment was analyzed by a randomized block design analysis of variance with three blocks. Subsets of the treatments (parents, F1's, and F2's) and orthogonal contrasts (parents vs. F1 and F2, F1 vs. F2; parents and F1 vs. F2, wide F1 vs. wide F2 [fineness]; wide F1 vs. narrow F1, wide F2 vs. narrow F2 [fineness]; wide F1 vs. narrow F1, wide F2 vs. narrow F2 [length/strength]) were analyzed. When environmental influence is high, strength and standard fineness show more variability in the F2 than in the F1 hybrid. The higher variability for strength and standard fineness disappears when environmental influence is minimal; the variability that does occur, both in the F1 hybrid and in the F2 hybrid, appears to be a function of original parental variability, especially for fiber fineness or agronomic properties. When original parental variability was low and the strength and standard fineness of the two parents were similar, fiber variability in the F2 hybrid was not greater than variability on a single plant in any generation.
Genetic Analyses of Male‐Fertility Restoration in Wheat: VII. A Fertility‐Inhibiting Gene
Authors: Du Hanlin , Maan Shivcharan S.
Published: July 2010

The cytoplasm of Triticum timopheevii Zhuk. has no apparent adverse effect on the cytoplasmic male‐sterile (CMS) plants of T. aestivum L. However, compared to the seed from A‐line/R‐line crosses, seed from A‐line/B‐line crosses have rough epidermis and reduced viability. Our objective was to compare the seed viability and fertility in plants with RfRf, Rfrf, or hemizygous Rf genes. We used CMS ‘Chris’ monosomics 1A and 6B, and four R‐lines. Lines L19 and L22 have Rf1 on chromosome 1A, and L11 and L13 have Rf4 on chromosome 6B. Sixteen BC1F1 families were obtained by crossing CMS Chris monosomics 1A and 6B to the four R‐lines and backcrossing 1A and 6B monosomic F1's to the corresponding R‐lines and euplasmic Chris. Eight controls were obtained by crossing four euploid F1's to the corresponding R‐lines and euploid Chris. The results showed that (i) Chris has a fertility inhibiting (Fi) gene and all four R‐lines have an fi and a defective‐seed (dfs) gene, (ii) fertility and seed viability were reduced to a greater extent in 6B monosomics than in 1A monosomics, (iii) aneuploidy affected the expression of Rf (and/or positive modifiers) and increased the expression of dfs more in crosses of L13 and L22 with a higher male‐fertility restoration potential than in crosses of L11 and L19 with a lower fertility restoration potential, and (iv) RfRf and FiFi were epistatic to dfsdfs, FiFi reduced the expression of Rfrf, but Dfs improved the viability of seed with rfrf fifi Dfsdfs embryos. It is proposed that the breeding of CMS A‐lines with fi, and R‐lines with positive modifiers of Rf genes, may facilitate male fertility restoration in Rfrf fifi wheat hybrids.
Nitrogen Metabolism of Soybean Genotypes Selected for Seed Composition, Fasciated Stem, or Harvest Index
Authors: Leffel Robert C. , Cregan Perry B. , Bolgiano Amanda P.
Published: July 2010

Development of methodologies for genetically increasing the efficiency of N metabolism in soybean [Glycine max (L.) Merr.] requires the identification of desirable genetic variation. Two field experiments were conducted at Beltsville, MD, to determine the genetic variability for measures of N metabolism among soybean genotypes selected for diversity in chemical composition of seed, podding habit, and harvest index. Nitrogen accumulation and partitioning, and N2 fixation were determined, the latter by the difference method utilizing the nonnodulating ‘Clark’ rjl genotype. Genotypes were evaluated at R5 (beginning seed) and R8 (full maturity) reproductive stages, to provide comparisons among genotypes for agronomic and N characteristics, including plant maturity; seed yield and protein; seed filling interval (R5 to R8); total harvest and total N harvest indices; pod N partitioning; and N2 fixation, N remobilization efficiency, and remobilized N. Results indicated that in most comparisons, high‐protein soybean exhibited a shorter seed‐filling interval, R5 to R8, as compared to low‐protein soybean. Measures of N metabolism that can contribute to enhanced N metabolism and seed yield and protein were generally lacking among diverse germplasm. Current cultivars were equal or superior to plant introductions or fasciated lines for measures of N metabolism.
Comparison of Lines Derived by Anther Culture and Single‐Seed Descent in a Spring Wheat Cross
Authors: Mitchell Melinda J. , Busch Robert H. , Rines Howard W.
Published: July 2010

Anther culture has the potential to produce homozygenous lines from crosses more rapidly than most conventional breeding methods, but in wheat (Triticum aestivum L.) there have been only limited tests comparing the field performance of lines developed from crosses using these methods. This study was conducted to compare the performance of F1 anther culture‐derived doubled‐haploid (AC) lines and F4‐derived random lines obtained by single‐seed descent (SSD) from a cross of spring wheat. Forty AC lines and 40 SSD lines developed from ‘Chris’/MN7529 were evaluated for six traits (grain yield, grain protein, plant height, kernel weight, heading date, and harvest index) at two locations in 1988 and 1989. The mean of the SSD lines was consistently higher than the mean of the AC lines for plant height and for kernel weight. The SSD lines also had a higher mean grain yield than AC lines in 1988, under severe drought conditions, but not in 1989. The AC lines exhibited greater genetic variance for grain protein and had a larger proportion of high‐protein lines than SSD lines. No differences between methods for harvest index and heading date were found, with the exception of a slightly larger variance of the AC lines for harvest index in 1988. Upon comparison of the means of the highest 20% of the lines from each method for yield and protein, only the high‐protein AC lines were found to have a greater mean and this was in 1989 only. For all of the traits analyzed, an acceptable level of performance could be found among the AC‐produced lines, and selected lines were as agronomically desirable as those produced by SSD. However, there are often severe genotype limitations on the efficiency of doubled‐haploid line production via anther culture, resulting in smaller population sizes from which to select desireable lines than with the SSD method.
Inheritance of Slow‐Rusting Resistance to Leaf Rust in Wheat
Authors: Das Modan K. , Rajaram Sanjaya , Mundt Christopher C. , Kronstad Warren E.
Published: July 2010

Race‐specific resistance of wheat (Triticum aestivum L. emend. Thell.) to leaf rust (Puccinia recondita f. sp. tritici) is often short‐lived. Slow‐rusting resistance has been reported to be a more durable type of resistance. To exploit the advantages of this durability, genetic analysis of slow rusting is essential. Inheritance of slow‐rusting resistance to leaf rust was studied in F6 families of spring wheat in two field experiments. The F6 families resulted from two diallel crosses involving one fast‐rusting and either five or two slow‐rusting wheat genotypes. Parents and progenies were evaluated in replicated field trials under epidemics initiated by artificial inoculation. The area under disease progress curve (AUDPC) was used to measure rust severity over time. Significant differences in AUDPC were observed among crosses and among progeny within crosses. Mean AUDPC values of crosses ranged from 16 to 538. Predominantly additive genetic variance for slow rusting was detected, but additive × additive genetic variance also was present. Narrow‐sense heritability varied from 45 to 92%, depending on the cross. Correlation coefficients between slow rusting and plant maturity were negative and low. Positive but low correlation coefficients between plant height and slow rusting were observed. Results indicated that early‐generation selection for slow‐rusting resistance to leaf rust in wheat should be effective, and would not be significantly influenced by either plant height or plant maturity.
Genetic Effects Associated with Reciprocal Recurrent Selection in BSSS and BSCB1 Maize Populations
Authors: Keeratinijakal Vichien , Lamkey Kendall R.
Published: July 2010

Reciprocal recurrent selection (RRS) was designed to capitalize on both additive and nonadditive genetic effects for improvement of the cross between two populations by complementary changes in allelic frequencies between populations. Eleven cycles of RRS have been completed in the Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic No. 1 (BSCB1) maize (Zea mays L.) populations. The objectives of this study were to partition the response to selection into that due to additive and dominance genetic effects and to evaluate the effects of genetic drift. A population diallel of the CO, C4, C7, C9, and Cll cycles of BSSS(R) and BSCB1(R) the C8 and C10 inte rpopulation crosses of BSSS(R) and BSCB1(R) were evaluated. The populations per se selfed and interpopulation crosses selfed of the CO, C4, C7, C8, C9, CI0, Cll cycles also were included in the study. The study was evaluated at four locations in 1988 and three locations in 1989. The response of the interpopulation cross for grain yield was 0.28 ± 0.04 Mg ha‐1 cycle‐1 and was primarily due to dominance effects. Responses in the populations per se, adjusted for the effects of genetic drift, were similar to the direct effects in the interpopulation cross. Improvementin BSSS(R) was due to both additive and dominance effects, but only dominance ffects were important in BSCBI(R). The results showed that selection response occurred at loci with alleles with partial to complete dominance with no evidence for overdominant alleles contributing to selection response. There were no significant changes in grain moisture, and the responses for root and stalk lodging were in the desired direction. It is concluded that RPS was effective for improving the interpopulation cross and inbreeding depression from genetic drift limited the observed response in the populations per se.