bluuebunny/crossref_metadata_2025 huggingface dataset:
Alfalfa Growth Response to a Zone‐Production System. I. Forage Production Characteristics1
Authors: Rechel E. A. , Carter L. M. , De Tar W. R.
Published: July 2010

In extant agricultural systems there is no long‐term predisposition to discriminate between trafficked and nontrafficked areas. The zoneproduction system, where all tractor traffic is confined to specific tracks or zones, offers a plausible alternative for improving crop productivity. This study was undertaken to compare how these two agricultural systems affect basic growth parameters of alfalfa (Medicago saliva L.). For two harvest cycles examined in 1984, final dry matter production in the zone‐production system was 687 g m−2, compared with 385 to 329 g m−2 for alfalfa subjected to various degrees of tractor traffic. In 1985 final dry matter production was 396 g m−2 in the zone‐production system, and 353 to 282 g m−2 when subjected to traffic. Maximum growth rate was 38.8 g m−2 day−1 in the zone‐production system and 26.6 to 16.0 g m−2 day−1 when subjected to traffic. The results from 1985 were similar with 27.1 g m−2 day−1 compared with 25.0 to 4.5 g m−1 day−1. The effect of traffic on alfalfa growth was not transitory, but it altered crop growth parameters for the whole harvest cycle. The zone‐production system created an environment more conducive to greater crop productivity by reducing alfalfa crown and shoot regrowth damage and soil compaction caused by traffic.
Honeycomb Design for Selection among Homozygous Oat Lines1
Authors: Robertson L. D. , Frey K. J.
Published: July 2010

The honeycomb design has been proposed for evaluating the yielding ability of single plants of small grains. The objective of this study was to assess the effectiveness of selection for grain yield via grain, adjusted grain, and biomass yields of single plants grown in a honeycomb design. Materials were 236 F10‐derived lines of oats from a broad‐based bulk population. They were tested as individual plants in two replicates of the honeycomb design in each of five environments and as lines in a hill‐plot experiment with three replicates in each of three environments. Mean yields from the latter experiment were used as the standard for measuring selection effectiveness. Pooled correlations for grain, adjusted grain, and biomass yields of single plants with grain yield of oat lines measured in hill plots were 0.29 ± 0.06, 0.27 ± 0.06, and 0.37 ± 0.06, respectively. With a 10% selection intensity, the actual gain in grain yield (expressed as a percentage of the hill‐plot population mean) of oat lines averaged 9.8 ± 0.05, 8.3 ± 0.06, and 11.0 ± 0.05, respectively, when grain, adjusted grain, and biomass yields of single plants were the selection criteria. Discarding of the lowest 10, 25, and 50% of plants for grain, adjusted grain, and biomass resulted in the average retention of 97, 90, and 70%, respectively, of the top decile of oat lines for grain yield. Our results suggest that selecting for grain or biomass yield of oat plants grown in a noncompetitive field arrangement can identify higher yielding oat lines. Selection for biomass gave about one‐seventh more gain than did selection for grain yield. Adjustment of grain yield of a plant according to the mean of six neighboring plants in the honeycomb design reduced the predicted gains from selection.
A Procedure to Identify Genes Affecting Maturity Using Soybean Isoline Testers1
Authors: McBlain B. A. , Bernard R. L. , Cremeens C. R. , Korczak J. F.
Published: July 2010

Maturity genes in soybean [Glycine max (L.) Merr.] have been discovered through accidental cotransfer during backcrossing of other traits. This study evaluated a test for identification of maturity genes in soybean strains that does not require backcrossing such genes into a common genetic background. All eight maturity isolines with homozygous combinations of the genes E1 el, E2 e2, and E3 e3 have been developed by backcrossing with the cultivar ‘Clark’. These isolines were used in testcrosses with Clark, ‘Harosoy’, or ‘Mukden’. Maturity dates (R8) for single field‐grown plants of parental and populations were taken in 1982. In 1983, flowering dates (RI) were also recorded, and pod‐picked bulk F3 populations were included for the Harosoy testcrosses and Clark isolines. Genotypes were proposed after examining the changes in ranges and variances between testcrosses, and by comparison with the Harosoy and Clark testcross progenies in which the segregating loci were known. Harosoy and Clark were confirmed to have the alleles el e2 E3 and el E2 E3, respectively. The genes El and E2 could be detected singly or together using either flowering or maturity data. The gene E3 could not be reliably detected unless a photoperiod sensitivity follow‐up test was utilized. Mukden had the genotype e1e2e3. This test will allow the maturity genotype of unrelated soybean strains to be determined, and make discovery of other genes possible without backcrossing into a common genetic background.
Recurrent Selection for Reduced Tassel Branch Number and Reduced Leaf Area Density above the Ear in Tropical Maize Populations1
Authors: Fischer K. S. , Edmeades G. O. , Johnson E. C.
Published: July 2010

Tropical maize (Zea mays L) is characterized by large tassels, broad, long leaves above the ear, and by a low harvest index. This study was conducted to evaluate direct and correlated responses to selection for reduced tassel primary branch number and for reduced leaf area density above the ear (LADAE). Leaf area density above the ear was defined as (number of leaves above the ear ✕ mean area of leaves EL + 1, EL + 3)/(plant height — ear height) ✕ land area occupied per piano, where EL refers to the position of the ear leaf. Six cycles of full‐sib recurrent selection for each of these traits was conducted in each of two populations (‘Tuxpeño‐l’ and ‘Antigua‐República Dominicana’). In a third population, ‘ETO Blanco’, there was simultaneous selection for both traits. Evaluation of Cycles 0 and 6 of single trait selections and Cycle 0,2,4, and 6 of combined trait selection, plus checks, was at several plant densities at three locations in Mexico over 2 yr. Significant (P = 0.05) mean gains per cycle for tassel branch number, LADAE, grain yield, and harvest index were: (i) Tuxpeño‐l: selection for reduced tassel branch number:−7.4, not significant (NS), 2.2, and 2.4%; selection for reduced LADAE: −1.2, −3.8, NS, and 3.8%; (ii) Antigua‐República Dominicana: selection for reduced tassel branch number: −8.6, −1.6, 2.4, and 2.2%; selection for reduced LADAE: −5.7, −2.6, 2.0, and 2.2%; and (iii) ETO Bianco, selection for reduced tassel branch number and LADAE: −6.8, −1.8, 2.5, and 2.9%, respectively. The correlation between LADAE and mean maximum leaf width, after removing the population effect, was 0.95**, significant at the 0.01 probability level (13 df. In all populations, selections resulted in significant increases in the predicted optimum plant density for grain yield, significant decreases in the anthesis‐to‐silking interval, and a shorter interval from planting to 50% silking.
Isolation of Soybean Lines Capable of Nodulation and Nitrogen Fixation under High Levels of Nitrate Supply1
Authors: Betts J. H. , Herridge D. F.
Published: July 2010

Results from numerous studies indicate that the proportion of soybean [Glycine max (L.) Men.] crop N derived from N2 fixation ranges between 25 and 50% and rarely exceeds 75%. The remainder is taken up as NO−3 from the soil and the net effect of soybean cropping is depletion of the soil N pool. Therefore, a program was commenced to identify genotypes of soybean which were capable of high levels of nodulation and high rates of N2 fixation in the presence of NO−3. In the first year of screening, 489 genotypes of diverse origin were grown in sand, free of Bradyrhizobium japonicum prior to inoculation with effective strain CB 1809 (USDA136), in unreplicated, 14‐L free‐draining pots in a glasshouse and supplied with nutrients containing either zero or 2.5 mMNO−3. Plants were sampled at R2 for plant growth (shoot mass), for nodulation, and for the proportion of plant N derived from N2 fixation (relative abundance of ureides in xylem exudate and extracts of shoot axes and nodulated roots). From the original 489 genotypes, 66 “NO−3‐tolerant”, 9 “NO−3‐sensitive” and 12 others were selected for a second year of screening on the basis of an overall ranking index which related nodulation and N2 fixation (relative ureides) activity at 2.5 mMNO−3 to activity at zero NO−3. In year two, treatments were replicated twice; plant culture and sampling procedures were otherwise identical to those used in the first year. Variation in symbiotic activity at high NO−3 supply was again evident with between 5‐ and 13‐fold differences in the nodulation and ureide indices recorded. In both screenings, genotypes of Korean origin ranked first overall and provided three of the top 10 lines. Of the original 19 Korean genotypes, 15 (80%) were screened in year 2 and nine (47%) were identified for future evaluation. Only 5% of the other 470 genotypes were selected as “NO−3‐tolerant” after two years of screening. Isolation of genotypes, superior in nodulation and N2 fixation in the presence of NO−3 under both glasshouse and field conditions, should be achieved with further screening in a high‐NO−3 field soil.
Genetic Analysis of Different Amylose Levels in Rice1
Authors: Kumar Ish , Khush G. S.
Published: July 2010

Amylose content has a pronounced effect on the cooking and eating quality of rice (Oryza sativa L.). Inheritance of amylose content in five crosses of rice and their reciprocals involving low, intermediate, and high amylose parents was studied. The analysis was based on single grains in the parent, F1, F2, B1F1 and B2F1 generations. The genes for high amylose content were found to be completely dominant over those for low or intermediate amylose content. Low or intermediate amylose content in the crosses tested was found to be governed by a single gene having a major effect. Evidence that amylose content was also influenced by genes of minor effects, or modifiers, was also noted. The role of dosage effects in influencing segregation was stated and breeding strategies are discussed.
Ozone and Soil Moisture Deficit Effects on Nitrogen Metabolism of Soybean1
Authors: Flagler R. B. , Patterson R. P. , Heagle A. S. , Heck W. W.
Published: July 2010

Ozone can interfere with nitrogen metabolism of soybean [Glycine max (L.) Merr.], but the effect of O3 on nitrogen metabolism of field‐grown soybean has received only limited attention. A two‐year field study was conducted to determine the effects of soil moisture deficit and O3 on nitrogen metabolism of ‘Davis’ soybean. Two soil moisture regimes, well‐watered and water‐stressed (WS), were established using different irrigation frequencies. Ozone treatments ranged from 0.025 to 0.107 μL L−1 (7‐h day−1 seasonal means) and were charcoal filtered, nonfiltered, and two (1983) or four (1984) levels of 03 addition to nonfiltered ambient air entering open‐top field chambers. Growing conditions were quite different between the two years. The 1983 season was dry and hot throughout vegetative growth. In contrast, 1984 was wetter and cooler, with no requirement for irrigation during vegetative growth. Effects due to WS were more pronounced than those due to O3. Nitrogen fixation, estimated by the acetylene reduction (AR) technique, was decreased by both O3 and WS treatments in both years. As O3 concentration increased, there was a decrease in total AR activity and a more rapid decline of activity during reproductive growth. Water deficit decreased AR activity significantly both years. The activity of nitrate reductase (NR) was also decreased by WS treatments. Ozone effects on NR activity varied between years. Rates of N accumulation were generally lower in higher O3 and WS treatments. The partitioning of N among various plant parts and concentrations of N within plant parts were altered in WS treatments during all stages of growth and to a far lesser extent by O3 treatments during reproductive growth. While there were no significant O3 ✕ water regime interactions, the results demonstrate that soil water status has a pronounced effect on plant response to O3.
Feasibility Studies on Planting Corn Trials to a Stand1
Authors: Bowman D. T.
Published: July 2010

Researchers have historically stressed uniformity of plant stands in corn (Zea mays L.) yield trials to reduce variability. This has mandated that all trials be over‐planted and later thinned. For this study, field trials were conducted in seven environments to determine the feasibility of planting corn yield trials to a stand by planting at a seeding rate of 110% of desired stand; this was compared to the standard practice of overplanting and thinning. Ten hybrids in each of three maturity groups were randomly selected for the study. A split plot arrangement was used with whole plots consisting of hybrids and subplots consisting of thinning vs. no‐thinning of stands. Soil types were a Portsmouth sandy loam (fine‐loamy over sandy or sandy‐skeletal, mixed, thermic Typic Umbraquults) and a Goldsboro loamy sand (fine‐loamy siliceous, thermic Aquic Paleudults). Variables analyzed included yield, percentage of desired stand, and standard deviation of distance between adjacent plants. Planting to a stand (no‐thin) resulted in less uniform stands for all maturity groups; however, this did not produce significantly lower yields. Percentage of desired stand was equivalent between the two treatments for early and medium‐maturing hybrids but the no‐thin treatment produced significantly greater than 100% stands for the late‐maturing hybrids. Error variances and F values for analyzing yield among entries were comparable between the two treatments. Nonsignificant entry‐treatment and environment‐entry‐treatment interactions and equivalent stands suggest that planting to a stand is feasible.
Development and Characteristics of a Kleingrass Population with Reduced Post‐Harvest Seed Dormancy1
Authors: Tischler C. R. , Young B. A.
Published: July 2010

Kleingrass (Panicum coloratam L.) seed has a period of postharvest dormancy lasting approximately 0.5 yr. Six cycles of recurrent selection (selecting seedlings germinating within 3 days) for reduced post‐harvest dormancy were used to generate a plant population (LD‐6) in which germination of freshly harvested seed was approximately 90%, compared to 5 to 20% for unselected material. Four germination treatments (light, light‐acid, dark, dark‐acid) were applied to LD‐6, fresh dormant (non‐afterripened), and 1‐year‐old dormant seed (afterripened) at three temperature regimes (35/25°C, 25/15°C, and 40°C). Germination counts for the light treatments were continued for 27 days. Germination counts for the dark treatments were made only at 6 days. Comparisons of data from light‐ and dark‐grown treatments were based on total germination percentages at Day 6 only, while comparisons of light treatments were based on data for the entire 27‐day counting period. The LD‐6 seed performed similarly (but with higher germination percentages) afterripened seed (27‐day count) at all germination temperatures. Rankings of the three seedlots were the same at all temperatures in the light, with germination of LD‐6 being the highest and that of non‐afterripened being the lowest. Rankings were also consistent across temperatures for the acid treatments. Acid treatments significantly improved germination in all cases except for the afterripened seedlot at the alternating temperatures and LD‐6 at 25/15°C. In most cases for the light and light‐acid treatments, germination of seedlots was highest at 35/25°C and lowest at 40°C. Germination was uniformly low in darkness, but germination of dark‐acid treatments was normally higher than that of light treatments (6‐day counts). Coefficients of velocity (data from 27 days) were calculated as an index of rapidity of germination. In all cases, acid treatments had higher coefficients of velocity. Coefficients of velocity for LD‐6 were similar to those for the afterripened seedlot, indicating that selection for reduced dormancy did not increase speed of germination.
Aflatoxin, Zearalenone, and Deoxynivalenol in North Carolina Grain Sorghum1
Authors: Hagler W. M. , Bowman D. T. , Babadoost M. , Haney C. A. , Swanson S. P.
Published: July 2010

Reports of aflatoxins and zearalenone in grain sorghum (Sorghum bicolor L.) and their deleterious effects on swine prompted an investigation of grain sorghum grown in North Carolina. Studies were conducted from 1981 to 1985 to determine the effects of location, cultivar, grain moisture at harvest, and rainfall pattern on the presence of aflatoxins, zearalenone, and deoxynivalenol at harvest. Aflatoxin levels were very low in all studies. Significant location effects were detected for zearalenone in 1981, 1982, 1984, and 1985, and for deoxynivalenol in 1981,1984, and 1985. The location effect may be a function of rainfall wherein heavy rainfall during anthesis and early grain fill predisposes the crop to Fusarium mycotoxin contamination. Hybrid effects were significant at P <0.10 in 42% of the environments for zearalenone and in 17% for deoxynivalenol. Hybrid effects were significant for deoxynivalenol across environments in 1982 and 1984. Based on data collected in 1983 and 1984, there was no correlation between grain moisture at harvest and Fusarium‐induced mycotoxin levels. A survey of 17 grower bins in 1983 revealed zearalenone in all samples with an average concentration of 443 ng/g, while deoxynivalenol was found in five samples.
Quantification of Acremonium coenophialum in Tall Fescue Seed Using Near Infrared Reflectance Spectroscopy1
Authors: Hill N. S. , Petersen J. C. , Shelby R. A. , Dalrymple L. W. , Barton F. E.
Published: July 2010

Near infrared reflectance spectroscopy (NIRS) can be used to evaluate major feed quality components of forage. Our objective was to determine whether NIRS could measure a minor quality component, the endophyte (Acremonium coenophialum Morgan‐Jones and Gams) in tall fescue (Festuca arundinacea Schreb.) seed. Two‐hundred seed lots were assayed for endophyte content using two procedures: the enzyme‐linked immunosorbent assay (ELISA) and an aniline blue mycelium stain. From the 200 seed lots, 74 were selected to obtain an even distribution of sample numbers over a range of endophyte infection from zero to high. Calibration equations for predicting endophyte content were obtained by multiple linear regression of NIRS spectral data and laboratory values for each procedure from 56 of the 74 seed lots. Calibration equations were verified on the remaining 18 seed lots. Five wavelengths were necessary to obtain the best equations for endophyte concentrations for each laboratory assay. The squared correlation coefficients (R2) for the calibration equations were low for both assays (R2 = 0.53 and 0.74). Correlation coefficients for verification data were also low (r2 = 0.31 and 0.54). Adding the 18 verification samples to the calibration set increased r2 for the mycelium stain assay but decreased R2 for ELISA. We conclude that laboratory methods used to assay the endophyte in tall fescue seed do not have the precision and accuracy necessary to calibrate NIRS instrumentation for routine analysis.
Identification of Two Dominant Genes Conditioning Brown Stem Rot Resistance in Soybean
Authors: Hanson P. M. , Nickell C. D. , Gray L. E. , Sebastian S. A.
Published: July 2010

Brown stem rot (BSR), caused by Phialophora gregata (Allington and Chamberlain) W. Gains, is an important disease of soybean [Glycine max (L.) Merr.] especially in the North Central USA. This study was conducted to provide an additional generation of data to confirm the presence of a single dominant allele for BSR resistance in L78‐4094, to determine the number of alleles conditioning BSR resistance in PI437833, and to study the relationship between BSR resistant alleles in PI437833 and L78‐4094. Plants (F2) of LN78‐2714 BSR‐susceptible (S) × L78‐4094 BS R‐resistant (R), F2plants and F,2:3 families of crosses PI437833 (R) × ‘Century’ (S) an PI437833 (R) × L78‐4094 (R) were inoculated in the greenhouse and evaluated for BSR resistance. Plants were classified as resistant or susceptible based on the presence or absence of leaf necrosis 5 weeks after inoculation. The BSR resistance in L78‐4094 is conditioned by a dominant allele, designated Rbs1, and the BSR resistance in PI437833 is governed by a dominant allele different from, Rbs1, designated Rbs2.
Inheritance of Stripe Rust Resistance among Near‐Isogenic Lines of Spring Wheat
Authors: Griffey C. A. , Allan R. E.
Published: July 2010

Increased range of virulence of stripe rust (Puccinia striiformis West.) on wheat (Triticum aestivum L.) in the northwestern USA has required assemblage of a broad genetic base of resistance. This study genetically differentiated among 14 sources of stripe rust resistance represented by near‐isogenic lines developed in stripe rustsusceptible ‘Lemhi 53.’ Plant reactions of the lines were evaluated in F1, F2, and BC1 populations from resistant by susceptible crosses and in F1 and F2 populations from resistant by resistant crosses. Greenhouse‐grown seedlings and field‐grown adult plants were tested for their reactions to the fungus. Most lines had resistance believed to be race‐specific, and the same gene(s) probably governed both their seedling and adult‐plant reactions. Other lines expressed only adult‐plant resistance, and some may have had different genes for each type of resistance. Segregation patterns from resistant by susceptible parent crosses suggested monogenic or digenic control of plant reaction to the fungus with digenic expression more common in the field. Some lines with resistance from ‘Brevor’ and ‘Alba’ and other lines with resistance from Alba, ‘Webster’, ‘Giza 139’/‘Gabo’ and ‘Ministre’ probably had gene(s) in common for reaction to the fungus. Some lines derived from Webster, Giza 139/Gabo, and ‘Soissonais’ had gene(s) in common for their adult‐plant reactions. The cross ‘Magnif 27’/5*Lemhi 53/3/T. spelta/‘Coastal’//6*Lemhi 53 expressed novel seedling resistance; wherein the F2 progeny derived from susceptible parents expressed digenic control of resistance. Genetic diversity was modest among the various lines, especially for seedling resistance.
Evaluation of Three Cycles of Recurrent Selection for Fruit Yield within a Population of Virginia‐Type Peanut
Authors: Monteverde‐Penso E. J. , Wynne J. C.
Published: July 2010

Recurrent selection with minimal crossing and single‐seed descent of S0 plants has been proposed as a breeding procedure for selfpollinated crops where hybridization is difficult. Three cycles of recurrent selection for fruit yield using a low selection intensity and little crossing were conducted in a genetically broad‐based population of Virginia‐type peanut (Arachis hypogaea L. ssp. hypogaea var. hypogaea). This study was conducted to (i) evaluate progress from selection for yield and (ii) estimate the realized heritability for yield as a function of the additive genetic variance in the population. Progress from selection was estimated using bulked seed of all selected lines within each parental group (BC experiment) and the mean of 20 randomly chosen lines from each parental group (EM experiment) to represent each of the cycles. The response to selection for fruit yield was linear across cycles with positive regression coefficients that were significantly different from zero for both experiments. Estimates of the progress of selection were 135 and 117 kg ha−1 per cycle for the BC and EM experiments, respectively. The proportion of selected individuals was 51, 43 and 50% for Cycles 0, 1, and 2, respectively. Selection based on fruit yield did not affect pod weight, pod length, seed weight, and seed count. Predicted progress was greater than observed progress in both experiments. The difference is an indication of possible nonadditive genetic variance as well as genotype ✕ environment interaction variance that inflated the estimate of heritability. Realized heritability, an estimate of narrow sense heritability in the base population computed by two different procedures, was about 30%. The recurrent selection procedure is simple, cost‐effective, and increased the mean yield of the population. The small differences in the results of the evaluation observed between the two experiments suggest that there is no advantage in using individual lines per plot to evaluate the response from selection in peanut.
Oxygen Requirements for Germination and Growth of Flood‐Susceptible and Flood‐Tolerant Corn Lines
Authors: VanToai T. , Fausey N. , McDonald M.
Published: July 2010

This study determined the oxygen requirement for germination and growth of flood‐susceptible and flood‐tolerant corn (Zea mays L.) lines. Such information is necessary for the establishment of more efficient drainage design criteria. In addition, the role of adenylate energy charge (AEC) in corn tolerance to anoxia was also evaluated. Two seed lots of five corn inbreds and five corn hybrids were germinated at constant (0, 2.5, 4.8, 10.5, 14.5, and 20.9 kPa) or fluctuating (daily fluctuations between either 0 and 20.9 kPa, or 2.5 and 14.5 kPa) O2. Percent seed germination, the number of adventitious roots, and shoot and root dry weight were determined after 96 h of treatment. The adenylatenergy charge (AEC) of inbred seeds germinated under constant O2 concentration was assessed by luciferin‐luciferase assay. The results indicated that flood‐tolerant corn lines could germinate at lower O2 concentrations than flood‐susceptible lines. The fluctuation between high and low O2 levels proved to be more damaging to germination and seedling growth than the compatible constant low O2 treatment. Corn plants apparently can tolerate prolonged anaerobic stress better than alternating periods of stress and nonstress. The germinated seeds from both flood‐tolerant and flood‐susceptible lines possessed similar adenylate energy charge (0.70 to 0.84). At low O2 concentrations, the number of seeds which possessed sufficient energy charge for germination was higher in the flood‐tolerant than in the flood‐susceptible lines. The positive correlation of adenylate energy charge and flooding tolerance indicated that flooding tolerance in corn is probably related to its ability to produce, or to conserve, metabolic energy under stress.
Herbage Growth and Carbohydrate Metabolism of Diploid and Tetraploid Alfalfa
Authors: Volenec J. J.
Published: July 2010

Polyploidy influences growth of alfalfa (Medicago sativa L.), but its impact on shoot and root carbohydrate metabolism and subsequent herbage regrowth rate remains unclear. This study related differences in herbage growth between isogenic diploid (2x) and tetraploid (4x) alfalfa populations to concentrations of root total nonstructural carbohydrates (TNC) and nonstructaral carbohydrate pools and dark respiration rates (RD) of meristematic shoot tissues. Leaf area, herbage weight, and taproots of plants were obtained weekly during 4 wk of regrowth in a controlled environment. Leaf area per plant and relative leaf area growth rate were approximately 100 and 33% greater, respectively, in the 4x population than in the 2x population. Although more herbage accumulated on 4x plants, herbage relative growth rates of populations were similar between Days 7 and 14, averaging 0.27 kg kg−1 d−1. Differences in shoot growth were not related to RD of shoot tip tissues, which averaged 55.2 ümol O2 mkg−1 s−1, or concentrations of glucose, sucrose, and starch in shoot tips. Root TNC concentrations of 2x and 4x populations were similar, initially averaging 360 g kg−1 dry wt. Concentrations of TNC increased in a linear fashion in roots of both populations during regrowth. The greater amount of shoot tissue present in the crown immediately following defoliation, along with the larger mass of individual growing shoot tips, contributed to more rapid leaf area development and faster herbage regrowth of the 4x population than the 2x population.
Mitochondrial DNA Diversity in Oat Cultivars and Species
Authors: Rines H. W. , Gengenbach B. G. , Boylan K. L. , Storey K. K.
Published: July 2010

Electrophoretic gel patterns of endonuclease restriction digests of mitochondria! DNA (mtDNA) isolated from oat (Arena sativa L.) cultivars and other Avena spp. were examined for banding pattern differences indicative of cytoplasmic diversity. A knowledge of oat cytoplasmic diversity would he useful for assessing vulnerability of cultivars to pathogens, for elucidating phylogenetic relationships among Avena spp., and in testing for nuclear‐cytoplasmic interactions favorable to increased plant growth. The restriction enzymes Xhol, Pstl, BamHl, and HindIII were used to digest mtDNA isolated from 7‐d‐old etiolated oat seedlings. Among eight cultivars, variations in mtDNA patterns were observed for one band in Xhol, Baml, and HinDall digests and two in PST digests. Exploit wild oat lines, including three A. sterilis L. and two A. fatua L. accessions, had mtDNA patterns very similar or identical to the cultivars. Patterns of two AABB genome tetraploids, A. abyssinica Hochst. and A. barbata Pott, and two AA genome diploids, A. strigosa Schreb. and A. canariensis Baum, Rajhathy et Sampson, differed from A. sativa ‘Victory’ by two to six bands, depending on the species and endonuclease. The CC diploid A. ventricosa Bal. cytoplasm mtDNA digest differed in at least 10 to 12 bands from the Victory mtDNA pattern. The AA and CC results are consistent with the idea that the cytoplasms of the hexaploid and tetraploid oats are derived from an AA‐genome and not a CC‐genome Avena diploid progenitor. The different mtDNA banding patterns of the diploids and tetraploids compared to the hexaploids indicate that the lower ploidy species may serve as a source for introgressing increased cytoplasmic diversity into hexaploid cultivated oats.
High Temperature Effects on Seedling Emergence and Embryo Protein Synthesis of Sorghum
Authors: Ougham H. J. , Peacock J. M. , Stoddart J. L. , Soman P.
Published: July 2010

High soil temperatures (>45°C) inhibit the field emergence of sorghum [Sorghum bicolor (L.) Moench] in the semiarid tropics. The objective of this study is to demonstrate that the measurement of embryo protein synthesis (EPS) is convenient an d rapid technique for the assessment of sorghum emergence at high soil temperatures. Two experiments were conducted, one using four landrace accessions and another using 14 commercially available lines. Seedling emergence was measured in a large water bath containing a series of soil‐filled clay pots. The temperature of the soil in the pots could be regulated (35–50°C) using infrared lamps. Protein synthesis was measured by incubating embryo‐containing half‐seeds with 14C‐labeled amino acids at different temperatures (35–40°C); the resulting labeled proteins were extracted for counting. The relative rankings of the landraces with respect to EPS and emergence demonstrated that the EPS technique clearly distinguished between lines that were able or unable to emerge at 50°C. However, with the commercially available lines, despite the agreement between the ranking of EPS and emergence, two lines diverged from this relationship, which is attributed to the greater complexity of the overall emergence process.
Ozone Treatment of Forage: Structure and Digestibility of Different Types of Lignified Cell Walls
Authors: Akin D. E. , Morrison W. H.
Published: July 2010

Ozone has been reported to reduce the lignin concentration in forages and to improve cell wall digestibility. The objective of this work was to evaluate the effect of ozonolysis on cell wall structure of various lignified tissue types in forages. In vitro digestibility was evaluated gravimetrically and by scanning electron microscopy for leaf blades and stems of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] and for leaf blades of ‘Kentucky‐31’ tall fescue (Festuca arundinacea Schreb.) and ‘Booneo’ orchardgrass (Dactylis glomerata L.). Ozonolysis of bermudagrass increased the in vitro digestibility by 12.5 percentage units over control material, and further showed that the epidermis, parenchyma bundle sheath, and lignified xylem cells of the vascular bundles in leaf blades were made more available for microbial degradation. Ozonated bermudagrass stems showed greater degradation of the parenchyma tissue, and cell wall widths of the more recalcitrant xylem and sclerenchyma ring were reduced in width. Ozone affected the most resistant tissues, i.e., xylem cell walls, and increased their susceptibility to microbial degradation at the surface of cut ends of sections. Ozonolysis of leaf and stem sections cut at 20‐, 10‐, and 5‐mm lengths usually did not significantly (P > 0.05) increase in vitro digestibility of various lengths of leaves and stems of forages, indicating the inability to penetrate and improve tissue digestibility within intact sections. The ability of O3 to oxidize lignin without substantial losses of tissues may provide a means to elucidate the phenolic‐carbohydrate interaction in cell walls.
Genetics of Resistance to Aphid in Cowpea
Authors: Pathak R. S.
Published: July 2010

Aphid (Aphis craccivora Koch) is a major insect pest of cowpea [Vigna unguiculata (L.) Walp.] particularly in Africa and Asia, causing direct damage by removal of plant sap and indirect damage by transmitting mosaic viruses. The objectives of this study were to determine the inheritance of resistance to aphid in four resistant cultivars of cowpea and to determine if the genes for resistance were independent. The parental, F1, F2, and BC1 populations involving resistant × susceptible and resistant × resistant cultivars were evaluated in the screenhouse. Three‐day‐old seedlings were each infested with 10 apterous adult aphids and injury reactions were recorded 8 to 10 d after infestation by counting dead (susceptible) and surviving (resistant) seedlings in each population. The reactions of F1, F2, and BC1 populations arising from the crosses of four resistant cultivars, ‘ICV10’, ‘ICV12’, and ‘Tvu 310’ with susceptible cultivar ‘ICV1’, revealed that resistance in each of these cultivars was governed by a single dominant gene. Tests for allelism in the F1 and F2 populations from crosses between resistant cultivars indicated that the resistance of ICV10 and Tvu 310 is controlled by a common locus as are those of ICV11 and ICV12. The locus of the resistance gene in ICV10 and Tvu 310 is not linked to the locus of the resistance gene in ICV11 and ICV12. Thus, the resistance gene common to ICV10 and Tvu 310 was nonalletic to, and independent of the resistance gene of cultivars ICV11 and ICV12. The gene symbols Rac1 and Rac2 (resistance to A. craccivora were assigned for the nonallelic and independent loci controlling this trait.
Measurement of Genetic Diversity among Popular Commercial Corn Hybrids
Authors: Troyer A. F. , Openshaw S. J. , Knittle K. H.
Published: July 2010

Genetic vulnerability of corn (Zea mays L.) has increased repeatedly since the growing of hybrid corn, single cross hybrids, and popular hybrids. We definite genetic vulnerability as the potential susceptibility of a crop to future attack by some biological or environment stress due to growing large numbers of a uniform biotype over large geographical areas. Genetic diversity, which usually decreases genetic vulnerability, has lacked a good method for measurement. The purpose of this study was to develop and test a method for measuring genetic diversity of corn and to assess genetic vulnerability in the U.S. Corn Belt by comparing genetic diversity of popular hybrids between two major and seed companies. Genetic diversity was estimated by the formula: GD = 1‐[(H‐C)/(H‐S)], where GD equals genetic diversity, H equals the average performance of the two hybrids, C equals the hybrid‐by‐hybrid cross, and S equals the average of the selfed hybrids. The method assumes heterosis is caused by some degree of dominance and epistasis is absent. A higher than average performing cross of two hybrids (less inbreeding depression) indicates more genetic diversity between the hybrids while lower than average performance of the cross (more inbreeding depression) indicates less diversity. Data were collected for grain yield, time to flower, grain moisture, and plant height on five popular hybrids from each of two major seed companies. Results for yield provided more precise estimates of GD than other performance traits measured. Genetic diversity averaged 0.74 and ranged from 0.17 to 1.37 and 0.28 to 1.12 among hybrids within companies. The GD estimate for the two most popular hybrids of 1985, 3732 and T1100 was 0.94. Our results help those needing a method to measure genetic diversity and should also encourage those concerned about genetic vulnerability in corn.
Soybean Plant Introductions with Resistance to Races 4 or 5 of Soybean Cyst Nematode
Authors: Anand S. C. , Gallo K. M. , Baker I. A. , Hartwig E. E.
Published: July 2010

Soybean cyst nematode (1Heterodera glycines Ichinohe) (SCN) is a serious pest of soybean [Glycine max (L.) Merr.) in the southern USA. A major portion of the U.S. soybean collection has not been screened for races of SCN. Approximately 9000 soybean plant introductions (PIs) were screened for their reaction to SCN races 4 and 5 in the greenhouse. The seedlings were grown in soil infested with SCN, and white females on the roots were counted. We found 21 PIs with some level of resistance to either race 4 or 5. A total of seven resistant, three moderately resistant, and two moderately susceptible PIs for race 4 were identified. Two PI's were heterogeneous for resistant and moderately resistant reactions. For race 5, seven PIs were resistant, two showed moderate resistance, two were moderately susceptible, whereas one segregated for resistant and moderately resistant reactions. All PIs showing resistance to races 4 or 5 were earlier reported to be resistant to race 3 and are in either Maturity Group II, III, or IV. PI 437654 was resistant to both races 4 and 5. In additional tests, it was found to be resistant to five races (races 1 through 5) of SCN. PI 437654 is the only PI resistant to all five recognized races of SCN and would be a good source in resistant cultivar development. These PIs are available to the researchers from the USDA soybean germplasm collection.
Heritability of Tolerance to Soybean Cyst Nematode in Soybean
Authors: Reese P. F. , Boerma H. R. , Hussey R. S.
Published: July 2010

Tolerance to Heterodera glycines Ichinohe, soybean cyst nematode (SCN), has recently been identified as an additional control strategy to limit yield losses in soybean, Glycine max (L.) Merr. Heritability estimates are necessary for determining breeding strategies to increase tolerance to SCN. The objectives of this study were to determine the heritability of tolerance in three soybean crosses and determine the degree of association between tolerance and seed yield in untreated and nematicide‐treated plots. A tolerance index (TI) was calculated using the formula: (seed yield of untreated subplot ÷ seed yield of nematicide‐treated subplot) ✕ 100. Fifty‐four F2‐derived lines in the F4 and F5 generations and parents were evaluated for TI in SCN‐infested soil for 2 yr at two locations. The Athens, GA location was infested with SCN Race 3 and Waynesboro, GA with SCN Race 4. Heritability for TI averaged 19% based on variance component estimates (three replications and two locations) and 26% for realized estimates (selection of top 11% of lines based on two‐location means). There was a positive association between TI and seed yield in untreated subplots (r = 0.78 to 0.90), but there was an inconsistent association between TI and seed yield in nematicide‐treated subplots. The variance component estimates of heritability for seed yield in untreated subplots averaged 31% (three replications and two locations). These results indicated that susceptible genotypes can be evaluated for seed yield without nematicides in SCN‐infested soil in the early phases of a breeding program to increase tolerance.
A Whole Plant Microculture Selection System for Kentucky Bluegrass
Authors: Pieper M. A. , Smith M. A. L.
Published: July 2010

Breeding advances in turfgrasses are constrained because environmental variation makes it difficult to identify and select useful traits in conventional field plots. A continuous whole plant microculture system for Kentucky bluegrass (Poa pratensis L.) was therefore developed as a practical selection and testing tool, consistent source of explants, and rapid means of propagation for new clonal selections. Stable, fully differentiated grass plant microcultures were readily produced on hormone‐free medium and maintained indefinitely by nodal subculture with greater efficiency than those produced by seed or greenhouse node explants. Advantages of these whole plant microcultures over test plants grown in vivo (highly regulated environment, compact and portable vessels, root systems that can be observed over time without intruding the growth environment) were illustrated in two different experimental applications. Osmotic potential adjustments in response to environmental stress were effectively demonstrated under strictly regulated conditions using bluegrass leaves from microculture, and time course evaluations of root rot pathogen symptoms allowed quantitative assessment of disease progression in vitro. Microcultures were transplanted successfully into greenhouse conditions, allowing parallel in vitro and in vivo tests and multiplication of selection lines. The methodology is especially valuable because it results in continuous maintenance of stable, uniform, differentiated plants, and their direct use in research analysis. This experimental system has potential as a vehicle for directed research on turf and pasture grasses.
Gene H16 in Wheat for Resistance to Hessian Fly
Authors: Patterson F. L. , Foster J. E. , Ohm H. W.
Published: July 2010

PI 94587 durum wheat, Triticum durum Desf., has resistance to biotype L of Hessian fly, Mayetiola destructor (Say) that has not been genetically characterized. Two genes, H6 and H11 from PI 94587, have been transferred into separate lines and characterized previously. Lines with H6 or H11 do not have resistance to biotype L that PI 94587 has. Our objectives were to transfer the gene(s) responsible for resistance to biotype L from PI 94587 to a susceptible line, and to determine if the gene(s) was different from known genes providing resistance to biotype L. We used standard greenhouse and growth chamber methods of analysis to determine resistance of seedling progenies to biotypes D and L of Hessian fly. A single partially dominant gene pair providing resistance to biotype L was transferred from PI94 587 to a previously susceptible durum wheat line ND D6647. Genetic studies indicated the new gene was not H9, H14, or H15. Reactions to biotypes B, C, D, and L indicatyed it was not H10, H12, or the ‘Marquillo’ gene. The newly isolated gene is designated H16.
Comparison of Genes Controlling Race 1 Anthracnose Resistance in Arc and Saranac AR Alfalfa
Authors: Elgin J. H. , O'Neill N. R.
Published: July 2010

Resistance in ‘Arc’ alfalfa, Medicago sativa L., to anthracnose caused by race 1 of Colletotrichum trifolii Bain is conditioned by a single dominant gene, An1. A single gene with gene action like An1 conditions resistance to race 1 anthracnose in ‘Saranac AR’. This tudy was conducted to determine whether or not the gene in Saranac AR coding for resistance to race 1 of C. trifolii is the same An1 gene operating in Arc. Crosses between three simplex race 1 C. trifolii‐resistant clones each of Arc and Saranac AR were made, progeny were evaluated for resistance to race 1 of C. trifolii, and susceptible progeny discarded. Resistant progeny were testcrossed to a susceptible male sterile clone. Those progeny whose testcross lines segregated 1:1 were discarded and those that appeared to segregate as a 3:1 or 5:1 were evaluated further. Ultimately the actual segregation ratio was determined to be 5:1, thus indicating the gene in Saranac AR coding for resistance to race 1 of C. trifolii to be the same An1 gene occurring in Arc.
Nitrogen Stress Effects on Growth and Seed Yield of Nonnodulated Soybean Exposed to Elevated Carbon Dioxide
Authors: Cure Jennifer D. , Israel Daniel W. , Rufty Thomas W.
Published: July 2010

Limitations in nutrient availability apparently can restrict plant response to CO2 enrichment; however, the alterations in physiological processes associated with such restrictions have not been defined. This experiment was conducted to investigate certain physiological responses of N‐limited soybean [Glycine max (L.) Merr. cv. Lee] plants growing in a CO2 enriched environment and to examine their role in determining growth and yield. The nonnodulating soybean plants were grown to maturity in controlled environment chambers at 350 or 700 μL L−1 CO2 and at 0.05, 1.0, 2.5, 5.0, or 10.0 mM KNO−3 supplied in nutrient solution. Substantial increases in whole‐plant growth and seed yield occurred in both CO2 treatments with increasing nitrate levels; the increases were greater, however, at high CO2. At all NO−3 levels except the lowest, exposure to high CO2 resulted in increased total leaf area, mean net assimilation rate, NO−3 uptake, and N utilization efficiency. Increased NO−3 uptake was associated with larger root systems, as uptake per unit of root mass was lower than controls. Carbon dioxide enrichment had little effect on dry matter partitioning among plant parts or harvest index. Alterations in partitioning were related to differences in NO−3 supply. The results suggest that atmospheric CO2 enrichment can stimulate seed yield of soybean even when the availability of N in the rhizosphere is limited.
Measurement of Instantaneous Nitrogen Use Efficiency among Pearl Millet Genotypes
Authors: Alagarswamy G. , Gardner J. C. , Maranville J. W. , Clark R. B.
Published: July 2010

Nitrogen is often a limiting factor in pearl millet [Pennisetum glaucum (L.) R. Br.] production. Genotypes are known that differ their response to N. In this study four pearl millet genotypes, which were previously identified as extremes in N use efficiency (total above ground biomass/unit of N absorbed) in the field, were compared in nutrient solution culture for their response to N supply and the instantaneous measurement of photosynthetic N efficiency (μmol CO2 g−1 N s−1). The latter component possibly contributes to N use efficiency. N‐efficient genotypes, ‘Souna B’ and 700112, and N‐inefficient genotypes, ‘BK560’ and ‘BJ104’, were grown at four N levels containing 60, 120, 180, and 240 mg N plant−1. Specific leaf area (cm2 g−1) was calculated from an accompanying growth analysis. Leaf CO2 exchange rate was measured on several leaves as they became fully expanded. Photosynthetic N efficiency was derived using values of leaf N concentration. Nitrogen‐efficient genotypes maintained thicker leaves (316.1 vs. 332.5 cm2 g−1) and were generally less responsive in terms of leaf N concentrations and leaf CO2 exchanger ate (CER) to the N available in solution as compared to the N‐inefficient genotypes. Souna B, the most efficient genotype, maintained a stable CER across all N levels. Photosynthetic N efficiency was similar for all genotypes except BK560, which was 10 to 15% less efficient. The small difference in photosynthetic N efficiency among genotypes coupled with relatively high photosynthetic N efficiency values of BJ104 (N‐inefficient genotype) suggests that differences in instantaneous measures of N use efficiency occurring during photosynthesis offer little explanation for overall differences in N use efficiency among these genotypes in a previous field study. Nitrogen use efficiency was more related to the partitioning of N resources available into additional leaf area.