bluuebunny/crossref_metadata_2025 huggingface dataset:
Sugar Metabolism during Growth and Development in Sugarcane Internodes
Authors: Lingle Sarah E.
Published: July 2010

Development of sugarcane (Saccharum spp. hybrids) genotypes with higher sucrose concentrations is desirable. Activities of sucrosemetabolizing enzymes during development of internodal storage tissue may determine the rate of total sugar accumulation and final sucrose concentration. Internodes of seven commercial cultivars were tagged prior to elongation and sampled at intervals from July until December during two growing seasons. Internode elongation was completed by about 380°C d (base temperature 18°C). Dry matter accumulated until about 800°C d. Water content decreased from about 920 to about 720 g kg−1 fresh weight (FW). Soluble acid invertase and sucrose synthase (sucrose cleavage direction) had peaks of activity during elongation, then declined to lower levels. Neutral invertase and sucrose‐phosphate synthase activities increased during development. Sugar accumulated, and the sucrose to total sugar ratio approached 1.0 as internodes developed, although the combined sucrose cleavage activity of the invertases and sucrose synthase in most internodes was greater than the synthetic activity of sucrose‐phosphate synthase. Sugar accumulation rate was not consistently correlated with activity of any enzyme assayed. Sucrose content during internode development was correlated with sucrose‐phosphate synthase activity and the difference between sucrose‐phosphate synthase and acid invertase activities. Sucrose content of mature internodes was not correlated with any enzyme activity. The data do not support the hypothesis that sucrose synthase activity is related to the rate of sugar accumulation, but do support the hypothesis that sucrose‐phosphate synthase and acid invertase play key roles in determining sucrose concentration during maturation in sugarcane internodes.
Heritabilities of Water‐Use Efficiency Traits and Correlations with Agronomic Traits in Water‐Stressed Alfalfa
Authors: Ray Ian M. , Townsend M. Shaun , Muncy Cherokee M. , Henning John A.
Published: July 2010

Inadequate supplies of surface water limit forage production in the southern Great Plains and western United States. Alfalfa (Medicago sativa L.) production in this region may benefit from improvements in water‐use efficiency (WUE), the amount of forage and root biomass produced per unit of water transpired. If benefits from improved WUE are to be realized, correlations between important agronomic traits and key physiological traits associated with WUE must be determined under water‐limited conditions. This study characterized genetic correlations among C isotope discrimination (Δ), canopy temperature, ash concentration, dry‐matter yield, forage maturity, and leaf‐to‐stem ratio (LSR) in alfalfa grown under water‐stressed field conditions. Heritabilities of the traits on a progeny mean basis were also determined. Thirty semidormant half‐sib families were evaluated in seeded plots that were irrigated every 30 d during 2 yr near Las Cruces, NM. Carbon isotope discrimination was negatively correlated with canopy temperature and ash content. An increase in dry‐matter yield was associated with higher Δ, lower canopy temperatures, low ash concentration, taller shoots, earlier maturity, and reduced LSR. Carbon isotope discrimination, ash concentration, and yield were moderately heritable (h2 = 0.4–0.56) indicating that these traits could be altered through breeding and selection. The positive relationship between Δ and shoot yield suggests that germplasms should be evaluated for both Δ and yield when characterizing alfalfa for high WUE to minimize potential yield reductions that may result from selection based only on Δ. Moderate correlations between Δ and canopy temperature or ash content indicated that neither trait provided highly reliable estimates of Δ in water‐stressed alfalfa.
Genetic Similarity Indices for Ancestral Cotton Cultivars and their Impact on Genetic Diversity Estimates of Modern Cultivars
Authors: Van Esbroeck G. A. , Bowman D. T. , May O. L. , Calhoun D. S.
Published: July 2010

The accuracy of pedigree‐derived genetic‐distance estimates depends on the availability of breeding records and on the validity of a number of assumptions. Pedigree analysis for cotton (Gossypium hirsutum L.) indicates a wide genetic base, which conflicts with other types of distance estimates indicating a narrow genetic base. The objectives of this study were to determine genetic similarity indices from agronomic and morphological traits for ancestral cotton cultivars and to determine their impact on the coefficient of parentage (CP) of recent cultivars. Twelve ancestral and two recent cultivars were grown at three locations (Clayton, NC; Florence, SC; and Stoneville, MS) during 1995 and evaluated for agronomic and fiber properties. Multivariate analysis of agronomic and fiber properties was used to create genetic similarity indices (s). There was little agreement between CP and s. Several ancestral cultivars developed from the earliest (pre‐1800) introductions into the USA were very similar to the most recent (post‐1900) introductions from Mexico. This suggested that all the original Mexican introductions were genetically very similar. Changing the assumptions in pedigree analysis to assume the original introductions were related by the average s among the ancestral cultivars (s = 0.38) decreased the level of diversity in frequently grown modern cultivars from CP = 0.16 to CP = 0.46 but had little effect on the relative ranking of cultivars. This occurred because effects of possible erroneous pedigree assumptions in distant generations became diluted. The high degree of similarity among ancestral cultivars suggests that pedigree‐derived genetic distance estimates have overestimated the genetic diversity among today's cultivars but not relative relationships.
Molecular Marker‐Assisted Dissection of Genotype × Environment Interaction for Plant Type Traits in Rice (Oryza sativa L.)
Authors: Yan Juqiang , Zhu Jun , He Cixin , Benmoussa Mebrouk , Wu Ping
Published: July 2010

A doubled haploid (DH) population of 123 lines from IK64/Azucena was used to analyze the genotype × environment (GE) interaction for eight plant type traits in rice (Oryza sativa L.). The total genetic effects were partitioned into genetic main effects and GE interaction effects. These two kinds of predicted effects were used in mapping quantitative trait loci (QTLs). Four to nine QTLs affecting different plant type traits were detected. Results indicated that all common QTLs detected in both environments were controlled by genetic main effects and some also by GE interaction effects. Some genomic regions identified significant QTL in only one environment; some also showed genetic main effects. Those QTLs with genetic main effects could be used in marker‐assisted selection across environments. For some other map regions, QTLs were controlled by only GE interaction effects without genetic main effects. Those QTLs could be included in marker‐assisted selection only for specific environments. In most cases, the pairs of traits with a high genetic correlation shared more common QTL regions than those pairs of traits with a lower genetic correlation.
Minimum Sample Size and Optimal Positioning of Flanking Markers in Marker‐Assisted Backcrossing for Transfer of a Target Gene
Authors: Frisch Matthias , Bohn Martin , Melchinger Albrecht A.
Published: July 2010

In recurrent backcrossing designed for introgression of a target allele from a donor into the genetic background of a recurrent parent (RP), molecular markers can accelerate recovery of the recurrent parent genome (RPG). The objectives of this study were to determine in marker‐assisted backcrossing (MAB) (i) the optimum distances (d1, d2} between the flanking markers and the target locus and (ii) the minimum number of individuals (n) required for obtaining with a certain probability a given number of individuals that carry the donor allele at the target locus and have a minimum proportion of donor genome on the carrier chromosome. Analytical solutions and tabulated results are given for relevant parameters (d1, d2, n) required to obtain, with a specified probability of success, at least one desired individual. They depend on the length of the carrier chromosome, the chromosomal position of the target locus, its distance to the flanking marker loci, and the number of individuals evaluated. Our approach can increase the efficiency of MAB by reducing the number of individuals and marker data points required.
Inbreeding Method Effects on Genetic Mean, Variance, and Structure of Recurrent Selection Populations
Authors: Jannink J. ‐L. , Abadie T. E.
Published: July 2010

Devising an optimal recurrent selection program within autogamous crops requires knowledge of which inbreeding method will provide the biggest short‐term and long‐term gains. We compared genetic gains using either doubled haploid (DH) or single seed descent (SS1)) methods by computer simulation of recurrent selection for high phenotypic value. The first simulation assumed an additive model with homogeneous recombination frequencies and allele effects. Genetic means and variances, number of fixed alleles, and linkage disequilibrium were modeled over 15 cycles of selection in a factorial of the two inbreeding methods, recombination frequencies between adjacent loci of 0.05, 0.15, 0.50, and environmental variances corresponding to initial heritabilities of 0.58, 0.26, and 0.13. The second simulation allowed for heterogeneity of recombination frequencies and allele effects. Short‐term gain determined by DH was superior. However, the difference in gain between DH and $SD declined as recombination frequency decreased from 0.50 to 0.05. At the two lower recombination frequencies, more (‐) alleles were fixed, and long‐term gain determined by DH was inferior compared with SSD. The recombination frequency heterogeneity treatment did not affect the response variables. The allele effect heterogeneity treatment increased short‐term and decreased long‐term gain but did not affect the relative performance of the two inbreeding methods. These results suggest that inbreeding method should be chosen on the basis of knowledge or assumptions about recombination frequencies between loci affecting the trait of interest.
Genetic Analysis of Frogeye Leaf Spot Resistance in PI54610 and Peking Soybean
Authors: Baker William A. , Weaver David B. , Qui Jiansheng , Pace Patrick F.
Published: July 2010

Frogeye leaf spot (FLS) of soybean [Glycine max (L.) Men.] is caused by the fungus Cercospora sojina Hara. The fungus is ubiquitous, but only problematic in hot humid soybean‐producing regions such as Brazil, China, Nigeria, and the southern USA. Significant yield losses (10–50%) are commonly associated with FLS epidemics. The quantification of unique alleles for resistance within the southern germplasm pool is an essential step toward developing a more usable set of differential genotypes and thereby clarifying the race situation within the C. sojina‐soybean interaction. Our objective was to determine the inheritance of resistance to FLS in PI54610 and Peking and their allelic relationship to Res,. ‘Lee’ soybean was used as a susceptible parent for crosses and control in all experiments. Parents and F2 seedlings were inoculated with a C. sojina spore suspension in the greenhouse or field and then rated for disease development 14 to 21 d later. On the basis of segregation ratios (3:1 resistant/susceptible in Peking × Lee and PI54610 × Lee, and 15:1 in ‘Davis’ × Peking and PI54610 × Peking), we found resistance in Peking was determined by a single dominant gene nonallelic to Rcs3. We also found, based on nonsegregation of resistance within the Davis × PI54610 population, that PI54610 has the same gene as in Davis (Rcs3). Resistance in Peking should be considered unique for the purpose of race differentiation and as a commercial source of resistance to FLS should Rcs3 fail.
Photosynthate and Dry Matter Partitioning in Short‐ and Long‐Season Cotton Cultivars
Authors: Pace P. F. , Cralle Harry T. , Cothren J. Tom , Senseman Scott A.
Published: July 2010

Differences in source‐sink relationships between short‐ and long‐season cotton (Gossypium hirsutum L.) cultivars, the contribution of main stem leaves to boll growth, and the distribution of nonstructural carbohydrates late in the season are not well understood. This study compared the cultivars Tamcot CAMD‐E (a short‐season type) and Stoneville 213 (a long‐season type) for two seasons in the field. To study photosynthate partitioning, the uppermost fully expanded leaf on the main stem subtending a reproductive axillary branch was pulsed with 14CO2 at the onset of reproductive growth (ORG) and at early reproductive growth (ERG), and sampled 48 h later. To study nonstructural carbohydrate partitioning, 14C‐starch was injected into the base of the main stem just above the soil surface durifig late reproductive growth (LRG). At ORG in 2 yr and ERG in the year with poor growing conditions, there were no cultivar differences in partitioning of accumulated dry matter throughout the plant or recent 14C‐photosynthate. However, at ERG in a year with good growing conditions, Tamcot CAMD‐E distributed a greater percentage (45%) of its dry matter to reproductive growth than did Stoneviile‐213 (30%). Tamcot CAMD‐E also partitioned 85% of its 14C‐photosynthate to the reproductive structures compared with only 60% in Stoneville‐213. Main stem leaves were an important source of photosynthate to the developing bolls in both cultivars and years. The total nonstructural carbohydrates of the main stem and root contained from 20 to 90% of the 14C‐photosynthate from the main stem leaves partitioned to the main stem or root at ORG and ERG. Both cultivars partitioned more than one‐half of the injected 14C‐starch to the main stem and its vegetative branches in both years at LRG. At this later stage of reproductive growth, cotton production could benefit from a different pattern of partitioning that favored the distribution of stored carbohydrates to reproductive structures.
Sink Characteristics of Reproductive Organs of Dwarf Bean in Relation to Likelihood of Abscission
Authors: Binnie R. C. , Clifford P. E.
Published: July 2010

In common with other grain legumes, dwarf bean (Phaseolus vulgaris L.) exhibits premature abscission of reproductive organs and concomitant reduction in harvestable yield potential. This problem was investigated by mapping 14C‐photosynthate partitioning to individual buds, flowers, and pods of dwarf bean plants growing in a controlled‐ environment cabinet. Experimental plants bore a single raceme for which probabilities of abscission at each reproductive site were determined beforehand with a separate batch of plants. Reproductive organs at proximal sites on the raceme had low probabilities of abscission and always received greater proportions of 14C‐photosynthate than did reproductive organs at distal sites with high abscission probabilities. The activity of reproductive organs as sinks in relation to their developmental stage and position on the raceme was also examined. Sink activity of reproductive organs was determined in this study as the percentage of total 14C‐activity imported by reproductive organs per dry weight of the organ expressed as a percentage of total dry weight of reproductive organs. Sink activities of reproductive organs could be ranked in the order buds > pods > flowers. Most importantly, it was clear that pods likely to abscise had reduced sink activity when at both the flower and bud stages compared with those likely to be retained. It is proposed that loss of sink activity by reproductive organs is a key event leading to their eventual abscission and an essential feature of the mechanism whereby pod number is controlled in grain legumes.
Temporal Shade on Creeping Bentgrass Turf
Authors: Bell G. E. , Danneberger T. K.
Published: July 2010

Creeping bentgrass (Agrostis palustris Huds.) turf exposed to shade during morning hours may decline more readily than similar turf exposed to afternoon shade. This study compared the quality and physiological responses of creeping bentgrass turf exposed to morning shade with turf exposed to afternoon shade and evaluated responses of the same species exposed to varying shade densities during the same period. Semipermanent shade structures were placed on a creeping bentgrass range maintained at a 6.4‐mm height. Structures provided 6 h of morning shade or 6 h of afternoon shade during the summer solstice. Each structure was covered with either 80 or 100% shade cloth and replicated three times. Control treatments of full sun and perpetual shade were also included. Treated turf was evaluated monthly for color, density, root mass, pigment concentrations, and total nonstructural carbohydrates (TNC). Regardless of response tested, no significant variation was found between plots receiving morning shade and afternoon shade or between plots in 80 and 100% shade. Canopy temperature, in comparison with air temperature, was 7% greater in morning shade than in afternoon shade, but the relationship between canopy temperatures in full sun and shade did not change during the day. Perpetual shade caused a 38% decrease in color and a 33% decline in density but treatments receiving 6 h of shade did not vary from the full sun treatment. Concentrations of chlorophyll a (46%) and b (50%), neoxanthin (31%), violaxanthin (44%), lutein (34%) declined in perpetual shade compared with full sun. Violaxanthin concentration was influenced by photosynthetic photon flux, suggesting its potential use as a shade stress indicator.
Quantitative Trait Locus Mapping of Ovicidal Responsein Rice (Oryza sativa L.) against Whitebacked Planthopper (Sogatella furcifera Horváth)
Authors: Yamasaki Masanori , Tsunematsu Hiroshi , Yoshimura Atsushi , Iwata Nobuo , Yasui Hideshi
Published: July 2010

The ovicidal response in rice (Oryza sativa L.) to whitebacked planthopper (WBPH), Sogatella furcifera Horváth, is characterized by the formation of watery lesions which result in the death of WBPH eggs. To determine the genetic mechanism of this ovicidal response, a set of 71 rice recombinant inbred (RI) lines (F8, F9, and F10) derived from a cross of japonica cultivar Asominori and indica cultivar IR24, the two parents, and the F1 were phenotyped for percentage of watery lesions (PWL) and WBPH egg mortality (EM). PWL and EM showed significant positive correlations (P < 0.001) and transgressive segregation was observed for both traits. A total of 10 quantitative trait loci (QTLs) for ovicidal response were detected with 292 RFLP markers in the F6 and F7 populations by composite interval mapping (LOD ≥ 1.5). Four of 10 QTLs coincided for PWL and EM and each three QTLs were only detected for PWL and EM. The QTL on chromosome 6 (R1954‐L688) was most significantly associated with the ovicidal response and accounted for 69.9% of phenotypic variance for PWL (F8) and 46.0% of phenotypic variance for EM (F8). Positive alleles for ovicidal response came from Asominori on chromosomes 1, 3, 6S (short arm), 8, and 12 and from IR24 on chromosomes 2, 6L (long arm), and 10. QTL accumulation from both parents was the genetic basis of the transgressive segregation in the RI population. No epistatic interaction was detected. The Asominori allele on the chromosome 6S QTL was essential to the ovicidal response, and R1954 was found to be a target marker for marker assisted selection.
Efficiency Gained by Screening Segregating Soybean Progenies with Soybean Cyst Nematode Race 2 versus Race 5
Authors: Young Lawrence D.
Published: July 2010

Soybean cyst nematode(SCN)(Heterodera glycines Ichinohe) is a major pest of soybean [Glycine max (L.) Merr.] in the USA and has many races. The use of SCN resistant cultivars effects changes in the ability of H. glycines field populations to parasitize these cultivars. The objective of this experiment was to determine if screening for race 2 resistance alone was sufficient to identify resistance for both races 2 and 5. Progenies of crosses involving ‘Hartwig” soybean were tested for resistance to either SCN race 2 or 5 in the F2 generation and for resistance to both races in the F2:3 generation in greenhouse studies. Individual plants were grown in soil infested with 1000 eggs of the appropriate race. Resistant plants were transplanted to the field for seed production. Progenies from the harvested plants were tested with both races in separate tests. All F2:3 progenies resistant to race 2 were also resistant to race 5. Only 64% of F2:3 progenies resistant to race 5 were also resistant to race 2. These results indicate that it is more efficient to screen for race 2 resistance alone than to screen for resistance to either race 5 or both races when resistance to both races is sought from crosses involving Hartwig.
Survival Characteristics of Corn Seed during Storage: I. Normal Distribution of Seed Survival
Authors: Tang Shande , TeKrony Dennis M. , Egli Dennis B. , Cornelius Paul L. , Rucker Marcy
Published: July 2010

Understanding the survival characteristics of hybrid corn (Zea mays L.) seed during storage is necessary to predict seed deterioration. This investigation tested one key assumption of the Ellis and Roberts viability equation, namely, that seed survival is normally distributed. Eleven corn seed lots (six hybrids) with little mechanical injury and a wide range in initial vigor were stored in various combinations of constant temperatures (20, 30, 40, and 50°C) and seed moisture contents (100, 120, 140, and 160 g kg−1, fresh weight basis). Seed‐survival curves were constructed by conducting successive germination tests at frequent intervals during storage. The χ2 goodness‐of‐fit test was used to evaluate the normality of survival curves constructed from either full or truncated (germination between 95 and 5%) data sets. When the data were truncated, the majority (79%) of the 187 survival curves analyzed were classified as normal (P > 0.05) or near‐normal [P < 0.05 but relatively small χ2, heterogeneity factor (H = χ2/df) < 10]. Only 57% of the curves from the full data set followed a normal or near‐normal distribution. Seed moisture and storage temperature had no consistent effect on the shape of the survival curves. Survival of low‐vigor seed lots was more likely to be normally or near‐normally distributed than was survival of high vigor seed lots. The assumption that seed survival is normally distributed was generally valid for truncated data sets of hybrid corn seed in constant storage environments.
Kentucky Bluegrass Seed and Vegetative Responses to Residue Management and Fall Nitrogen
Authors: Lamb P.F. , Murray G.A.
Published: July 2010

Open‐field burning to remove post‐harvest residue from Kentucky bluegrass (Poa pratensis L.) seed fields was essentially eliminated in Washington in 1998, and may be banned in Idaho and Oregon because of health concerns. Regulations banning burning necessitated exploring non‐thermal residue management. Seed and vegetative responses of six Kentucky bluegrass cultivars to three post‐harvest residue removal methods, and three timings of fall applied N in second‐ and third‐year seed crops were evaluated. Residue removal methods were burn, vacuum, and rake. Split fall timings of N applications were 70% September, 30% October; 30% September, 70% October; and 100% October. Post‐harvest residue management did not significantly influence second‐year seed crop yields; however, with mechanical residue removal, third‐year seed crop yields of ‘Glade’, ‘Huntsville’, and ‘South Dakota’ were 42 to 62% of seed yields with open‐field burning. Seed yield of ‘Baron’, ‘Limousine’, and ‘Georgetown’ was not affected by residue management in the third‐year seed crop. As larger portions of N were October applied, second‐year seed yields of Georgetown and Huntsville were higher. Third‐year seed crop yields were not influenced by timing of N application. Overall, seed production was correlated with panicle number , but not with above ground biomass, rhizome biomass, or weight per 100 seeds. These data suggest that seed yield of relatively short‐statured, small‐seeded cultivars producing modest amounts of above ground biomass may be sustained by mechanical residue removal through three seed crop years when 70 or 100% the N is applied in October.
Identification of suitable seed regeneration sites for photoperiod‐sensitive cowpea germplasm
Authors: Gillaspie A.G. , Goenaga R.J. , Torres S. , Peregrine E.
Published: July 2010

To determine an appropriate location to regenerate photoperiod‐sensitive cowpea [Vigna unguiculata (L.) Walp.], seed production and virus contamination data were measured at Isabela, PR, St. Croix, VI, and Griffin, GA for six photoperiod‐sensitive cowpea accessions. The results indicate that Isabela was best suited for seed regeneration of photoperiod‐sensitive cowpea. Seed production at Isabela was equal to or greater than that at either of the other two locations for these accessions. Virus infection of plants and of seeds was high at Griffin. However, little virus infection occurred at Isabela and at St. Croix. The systematic approach used in these tests can be used as a model for curators in the National Plant Germplasm System and others to determine the best environment in which to regenerate germplasm.
A device to measure turfgrass load bearing capacity under field conditions
Authors: Erusha K.S. , Shearman R.C. , Wit L.A.
Published: July 2010

Turfgrasses can bear some weight before they are crushed. This load bearing capacity (LBC) provides a cushioning effect that protects crown tissue from a certain degree of traffic injury and its subsequent stress. The more LBC a turf has, the less potential traffic injury may be expected. A device was designed, constructed, and tested under field conditions to measure turfgrass LBC. The LBC device was constructed to be lightweight and easy to handle. Operator‐applied pressure compressed the turfgrass canopy to a predetermined endpoint. The resistance required to reach this endpoint was measured as force (N 45 cm−2) by a load transducer. Values were converted to kN m−2 The device was used to measure LBC of mature turfs of ‘Texoka’ buffalograss [Buchloë dactyloides (Nutt.) Engelm.], ‘Parade’ Kentucky bluegrass (Poa pratensis L.), ‘Kentucky 31’ and ‘Mustang’ tall fescue (Festuca arundinacea Screb.), and ‘Meyer’ zoysiagrass (Zoysia japonica Steud.). The LBC device successfully separated turfgrasses species and cultivars. Zoysiagrass and buffalograss had the highest and lowest LBC values for the species tested, 10.7 and 1.19 kN m−2, respectively. Intraspecific differences of tall fescues were successfully separated; Mustang at 3.28 kN m−2 had a greater LBC than Kentucky 31 at 2.27 kN m−2 More testing is needed to assess the ability of the LBC device to detect potential differences among cultural practice treatments, like mowing heights and nutritional rates, and screening turfgrass selections for stiffness and rigidity.
Soybean Yield Potential—A Genetic and Physiological Perspective
Authors: Specht J. E. , Hume D. J. , Kumudini S. V.
Published: July 2010

Soybean [Glycine max (L.) Merr.] yields in the USA have risen 22.6 kg ha−1 yr−1 from 1924 to 1997, but in the last quarter century (1972–1997) have risen 40% faster, 31.4 kg ha−1 yr−1 This upward trend in on‐farm yield is fueled by rapid producer adoption of technologies emerging from agricultural research. Published estimates of the annual gain in yield attributable to genetic improvement averaged about 15 kg ha−1 yr−1 prior to the 1980s, but is now averaging about 30 kg ha−1 yr−1 in both the public and proprietary sectors. Periodic advances in agronomic technology, and a relentless rise in atmospheric CO2 (currently 1.5 μL L−1 yr−1), also contribute to the upward trend in on‐farm yield. In Nebraska, irrigated yield averages 800 kg ha−1 more than rainfed yield, and is improving at a 40% faster annual rate (35.1 vs. 24.9 kg ha−1). About 36% of the annual variation in the irrigated‐rainfed yield difference is attributable to annual variation in absolute rainfed yield. Inadequate water obviously limits absolute crop yield, but also seems to be an obstacle in terms of the rate of yield improvement. Several physiological traits changed during six decades of cultivar releases in Ontario that led to a genetic gain in yield of about 0.5% yr−1 Changes in some traits were obvious (improved lodging), but more subtle in others (greater N2‐fixation, greater stress tolerance). In terms of photosynthate supplied to sinks across a wide range of environments, recent cultivars seem to be superior to obsolete ones. To sustain and enhance soybean yield improvement in the future, technological innovation must be continually injected into the agricultural enterprise.
Yield Improvement in Temperate Maize is Attributable to Greater Stress Tolerance
Authors: Tollenaar M. , Wu J.
Published: July 2010

A retrospective analysis of the physiological basis of genetic yield improvement may provide an understanding of yield potential and may indicate avenues for future yield improvement. Rate of yield improvement of maize (Zea mays L.) hybrids in Ontario, Canada has been ≈1.5% yr−1 during the last five decades. Comparison of short‐season hybrids representing yield improvement from the late 1950s to the late 1980s showed that genetic yield improvement was 2.5% per year and that most of the genetic yield improvement could be attributed to increased stress tolerance. Differences in stress tolerance between older and more recent hybrids have been shown for high plant population density, weed interference, low night temperatures during the grain‐filling period, low soil moisture, low soil N, and a number of herbicides. Yield improvement is the result of more efficient capture and use of resources, and the improved efficiency in resource capture and use of newer hybrids is frequently only evident under stress. Improved resource capture has resulted from increased interception of seasonal incident radiation and greater uptake of nutrients and water. The improved resource capture is associated with increased leaf longevity, a more active root system, and a higher ratio of assimilate supply by the leaf canopy (source) and assimilate demand by the grain (sink) during the grain‐filling period. Improvements of resource use under optimum conditions have been small, as leaf photosynthesis, leaf‐angle distribution of the canopy, grain chemical composition, and the proportion of dry matter allocated to the grain at maturity (i.e., harvest index) have remained virtually constant. Genetic improvement of maize has been accompanied by a decrease in plant‐to‐plant variability. Results of our studies indicate that increased stress tolerance is associated with lower plant‐to‐plant variability and that increased plant‐to‐plant variability results in lower stress tolerance.
Nine Cycles of Recurrent Selection for Increased Groat‐Oil Content in Oat
Authors: Frey K. J. , Holland J. B.
Published: July 2010

Increases in the groat (caryopsis)‐oil content of oat (Avena sativa L.) raise the energy value of oat grain. Nine cycles of recurrent phenotypic selection for high groat‐oil content were conducted in a genetically broad‐based oat population that included germplasm from the wild relative A. sterilis L. Our objectives in this experiment were to determine if selection for high groat‐oil content was effective and if selection reduced genetic variation for oil content; to identify agronomically acceptable lines with high groat‐oil content; and to document the indirect effects of selection on grain yield, groat fraction, and oil yield. We evaluated 100 random lines from the base (C0) population and each of the nine selection cycle populations in three environments. Mean groat‐oil content increased linearly during nine cycles of selection at a rate of 6.6 g kg−1 cycle−1 (equivalent to 6.7% of C0 population mean cycle−1) from a mean of 98.2 g kg−1 in C0 to 158.5 g kg−1 in C9. The rate of gain from selection did not decrease in later cycles. Oil yield increased at a rate equivalent to 1.9% of C0 population mean cycle−1, while mean groat fraction did not change and mean grain yield decreased at a rate equivalent to 3.2% of C0 population mean cycle−1 For all traits, genetic variation did not decrease during selection cycles. Selected S0‐derived lines from the population with groat‐oil contents >150 g kg−1 exhibited lower yield, greater lodging, and greater disease susceptibility compared with the best check cultivar.
Molecular Mapping of the Rcs3 Gene for Resistance to Frogeye Leaf Spot in Soybean
Authors: Mian M. A. Rouf , Wang Tianyuan , Phillips Daniel V. , Alvernaz Jennie , Boerma H. Roger
Published: July 2010

Frogeye leaf spot (FLS) (caused by Cercospora sojina Hara) is a foliar disease of soybean [Glycine max (L.) Merr.] that causes significant yield loss in southeastern USA. The Rcs 3 gene in soybean has been reported to condition resistance to all known races of C. sojina. Molecular mapping of the Rcs3 gene will be helpful in breeding soybean for resistance to FLS. The objective of this study was to map the Rcs3 gene with DNA markers. The parents, 123 F2 plants, and the F2:3 families from the cross of ‘Blackhawk’ (susceptible) × ‘Davis’ (resistant and original source of the Rcs3 gene) were scored for FLS reaction in the greenhouse after inoculation with race 5 of C. sojina. In addition, ‘Wright’ and the Wright6‐Rcs 3 (near isoline of Wright) were also scored for FLS by the same protocol. A resistant and a susceptible DNA bulk were created by pooling the DNA of 15 resistant and 15 susceptible F2 plants, respectively, from the Blackhawk × Davis population. The two bulks and resistant–susceptible near isolines (NILs) of Wright were screened with simple sequence repeat (SSR) markers from soybean linkage groups with known disease resistance gene clusters. The bulks and the NILs of Wright both showed a putative association between the Rcs 3 locus and a SSR marker Satt244 from linkage group (LG) J. A molecular map of the relevant segment of the LG J for the Blackhawk × Davis population was then created by screening the DNA of 95 F2 plants with the available polymorphic SSR and RFLP markers. We have mapped the Rcs3 gene for resistance to FLS in soybean near a previously known disease resistance gene cluster on LG J. The gene was closely linked to SSR markers Satt244 and Satt547. Close proximity of this gene with these SSR markers provides soybean breeders with an opportunity to use these markers for marker assisted selection (MAS) for FLS resistance in soybean.
Growth of White Clover Ecotypes, Cultivars, and Germplasms in the Southeastern USA
Authors: Brink G. E. , Pederson G. A. , Alison M. W. , Ball D. M. , Bouton J. H. , Rawls R. C. , Stuedemann J. A. , Venuto B. C.
Published: July 2010

Naturalized populations, or ecotypes, of white clover (Trifolium repens L.) are found in many southeastern U.S. pastures, often persisting despite adverse environmental and cultural conditions. Our objective was to compare the growth, morphology, and vegetative persistence of white clover ecotypes (small‐ to medium‐leaf) with selected cultivars (large‐leaf) and improved germplasm under grazing in four southeastern states. Seed or stolons of white clover ecotypes were collected primarily from grazed pastures in spring 1994 in Louisiana, Mississippi, Alabama, and Georgia, and increased by intercrossing. Plots of seven ecotype collections, ‘Osceola’, ‘Regal’, ‘Louisiana S‐1’, ‘Grasslands Huia’, ‘Grasslands Prestige’, Brown Loam Synthetic No. 2 germplasm, and Southern Regional Virus Resistant germplasm were established in October 1995 in each state. Plots were stocked continuously with cattle (Bos taurus) (5‐cm stubble) from January 1996 to January 1998. Stolon length and axillary bud viability, and number of stolon apices, rooted nodes, and seedlings were measured every 3 mo. Stolon length of the ecotypes usually exceeded that of the cultivars and germplasm at all locations, particularly in the winter and spring. By the end of the experiment, the ecotypes also exhibited greater stolon branching than the cultivars and germplasm (1580 vs. 320 branches m−2). Superior vegetative growth of the ecotypes was attributed to a greater proportion of the stolon nodes being both branched and rooted, particularly during the summer. White clover ecotypes represent a valuable source of germplasm to incorporate into breeding programs or to develop directly into more persistent cultivars.
A Comparison of Winter Cereal Species and Planting Dates as Residue Cover for Cotton Grown with Conservation Tillage
Authors: Bauer Philip J. , Reeves D. Wayne
Published: July 2010

Winter cereals are often used as cover crops before planting cotton (Gossypium hirsutum L.). Black oat (Avena strigosa Schreb.) is the predominate cereal cover crop for cash crops in southern Brazil and Paraguay, but limited information is available on the suitability of black oat as a cover crop in the southeastern USA. The objectives of this study were to compare black oat with adapted winter cereals for this region and to determine the effect of cereal residue species and amount on cotton growth, N status, and lint yield. In a greenhouse study in which black oat and rye (Secale cereale L.) residues were mixed with soil, tap root elongation of both cotton and radish (Raphanus sativa L.) was inhibited more by black oat residue than by rye residue. In a field experiment on a Goldsboro loamy sand (fine‐loamy, siliceous, thermic Aquic Kandiudult), cotton was grown in 1995 and 1996 following black oat, oat (Avena sativa L.), rye, and wheat (Triticum aestivum L.) that were planted at three different times (October, November, and December). All four winter cereals had similar biomass production at each planting date in 1995. In 1996, rye was the only species not visibly damaged by a low temperature of −12.2°C that occurred during the winter. Black oat biomass was comparable to wheat in all planting dates but averaged 60% less than rye over all three planting dates and was 37% less than oat in the October planting date in that year. Black oat tended to have a higher N concentration than the other cereal species. Cotton plant density was lowest following black oat and rye. Cotton growth, leaf blade N, and petiole NO3‐N were more dependent on residue amount than on residue species. Cotton lint yield following black oat was 120 kg ha−1 higher than lint yield of cotton following rye. Cotton following black oat, wheat, and oat had similar lint yield. Black oat may be a promising cover crop for the southeastern USA, but evaluations of other cultivars and/or improvement programs to improve cold hardiness are needed to improve the utility of this species.
Leaf Reflectance Spectra of Cereal Aphid‐Damaged Wheat
Authors: Riedell Walter E. , Blackmer Tracy M.
Published: July 2010

The efficiency of field monitoring for insect pests would be improved with knowledge of reflected solar radiation from crop canopies during insect outbreaks. The objectives of this greenhouse study were to characterize leaf reflectance spectra of wheat (Triticum aestivum L.) damaged by Russian wheat aphids (Diuraphis noxia Mordvilko) and greenbugs (Schizaphis graminum Rondani) and to determine those leaf reflectance wavelengths that were most responsive to crop stress imposed by these aphid pests. When the ligule was visible on second oldest leaf, wheat plants were infested with four wingless adult Russian wheat aphids, four wingless adult greenbugs, or left uninfested (four replicate plants per treatment). Plants and aphid populations were allowed to grow under greenhouse conditions for 3 wk, after which leaf‐reflected radiation (from the adaxial surface across the 350–1075 nm range), dry weight, area, and chlorophyll concentrations were measured. When compared with the control, greenbug feeding damage caused general necrosis in oldest (first) leaves and dramatically lowered the dry weight, leaf area, and chlorophyll concentration of the second, third, and fourth leaves. Russian wheat aphid feeding resulted in a reduction in leaf dry weight and area in the third and fourth leaves, and a reduction in total chlorophyll concentration in all leaves. Leaf reflectance in the 625‐ to 635‐nm and the 680‐ to 695‐nm ranges, as well as the normalized total pigment to chlorophyll a ratio index (NPCI), were significantly correlated with total chlorophyll concentrations in both greenbug‐ and Russian wheat aphid–damaged plants. Thus, both of these wavelength ranges, as well as this reflectance index, were good indicators of chlorophyll loss and leaf senescence caused by the aphid feeding damage.
Nitrogen Fertilization and Supplementation Effects on Performance of Beef Heifers Grazing Limpograss
Authors: da C. Lima G. F. , Sollenberger L. E. , Kunkle W. E. , Moore J. E. , Hammond A. C.
Published: July 2010

Seasonally low N concentrations in ‘Floralta’ limpograss [Hemarthria altissima (Poir.) Stapf & C.E. Hubb.] limit intake and weight gain of growing animals. This research evaluated management alternatives for increasing summer weight gains of beef replacement heifers (Bos spp.) on limpograss pastures in Florida. Soils were sandy, siliceous, hyperthermic, aeric (Smyrna series) or ultic (Pomona series) Haplaquods. During 1992 and 1993, a factorial arrangement of two pasture N fertilization rates (50 and 150 kg ha−1) and three diet supplements (NONE, corn [Zea mays L.] plus urea [CU], and CU plus rumen undegradable protein [CUUP]) were studied in two replications of a completely randomized design. Supplementation with CU increased average daily gain (ADG) from 0.06 (NONE) to 0.41 kg on pastures fertilized with 50 kg N ha−1, but there was no ADG response to CU when N rate was 150 kg ha−1 When no supplement was fed, increasing pasture N fertilization from 50 to 150 kg ha−1 increased ADG from 0.06 to 0.36 kg. Grass crude protein (CP; 73 vs. 56 g kg−1) and in vitro organic matter digestion (IVOMD; 542 vs. 509 g kg−1) were greater at the higher N rate. Heifer plasma urea N (PUN) concentration was low (4.2 mg dL−1) when no supplement was fed and pastures received 50 kg N ha−1, suggesting that low CP was limiting ADG. These data indicate that N deficiencies of cattle grazing limpograss can be overcome by increasing rate of pasture N fertilization or by providing N supplements.
Factors Affecting Groat Percentage in Oat
Authors: Doehlert Douglas C. , McMullen Michael S. , Baumann Robert R.
Published: July 2010

The groat percentage represents an important quality characteristic of oat (Avena sativa L.). Our objectives were to characterize mechanical factors of the oat dehulling process and the physical characteristics of the oat grain that affect groat percentage. Mechanical factors were determined with a compressed air dehuller. Physical characteristics of oat grain were evaluated from 10 genotypes grown at three locations with digital image analysis. Groat percentage as determined by hand dehulling was compared with mechanical dehulling. The strength and duration of mechanical stress required to separate the hull from the groat and the strength of the aspiration required to remove free hulls from the groats had significant effects on groat percentage results. Insufficient mechanical stress resulted in ineffective dehulling, but excessive stress resulted in groat breakage. Excessive aspiration removed groats as well as hulls, but insufficient aspiration left excessive hulls with groats. Groat percentage values obtained by hand dehulling or by mechanical means correlated well. Hand sorting of mechanically dehulled groats to remove hulls remaining after dehulling improved their correlation, indicating the importance of hand‐sorting mechanically dehulled oats. Test weight and oat size uniformity were highly correlated with groat percentage. Negative correlation between hulls remaining after dehulling with groat percentage suggested that heavier hulls, associated with lower groat percentage, were more difficult to remove by aspiration. Positive correlations between groat breakage during dehulling and groat percentage suggest that thin hulls provide less protection to the groat during dehulling, resulting in higher levels of breakage.
Selection and Evaluation of Smooth Bromegrass Clones with Divergent Lignin or Etherified Ferulic Acid Concentration
Authors: Casler Michael D. , Jung Hans‐Joachim G.
Published: July 2010

Lignin and etherified ferulic acid (EthFA) are cell wall constituents believed to have important negative impacts on digestibility of forage cell walls. Our objective was to identify genotypes of smooth bromegrass (Bromus inermis Leyss) with unconfounded divergence in lignin and EthFA, such that their independent effects could be determined on in vitro fiber digestibility (IVFD). Eight clones were selected from each of four populations (‘Alpha’, WB19e, ‘Lincoln’, and WB88S). Selection was successful for EthFA in all populations except WB88S, creating repeatable divergence of 11.2 to 12.5%. Selection was unsuccessful for lignin concentration per se, most likely because of large genotype × environment interactions. Nevertheless, the resulting clones showed significant variation for both EthFA and lignin concentrations and these two variables were nearly independent among the selected clones. Both lignin and EthFA had significant negative effects on 96‐h IVFD, regardless of the statistical estimation method used. Across estimation methods, there was not a clear difference in the magnitude of the lignin and EthFA effects on IVFD. Both the total amount of lignin in the cell wall and the amount of ferulic acid cross‐linking lignin to polysaccharides via ether bonds appear to be under genetic control, and both components play a role in regulating the genetic potential for rumen degradation of cell walls in smooth bromegrass. These clones are a potential tool for conducting animal feeding trials using forages with relatively unconfounded differences in a single cell wall characteristic.
Genetic Diversity in Cotton Assessed by Variation in Ribosomal RNA Genes and AFLP Markers
Authors: Pillay M. , Myers G. O.
Published: July 2010

Variation in the ribosomal RNA genes (rDNA) and amplified fragment length polymorphism (AFLP) markers has been used to establish the extent of genetic diversity and relatedness in plants. The utility of these methods to detect inter‐ and intra‐specific variation in cotton (Gossypium spp.) has not been reported and could be useful in cultivar identification and in marker assisted selection. The objectives of this study were to: (i) determine the molecular organization of the rDNA genes by restriction enzyme mapping and (ii) assess the level of AFLPs in Old and New World species of cotton. A restriction site map of the rDNA gene structure of G. hirsutum L. cv. TM1 was constructed from DNA digested with 12 restriction enzymes and hybridized to heterologous probes. Four EcoRI‐MseI primer‐pair combinations were used for the AFLP analysis. The rDNA gene structure in cotton was found to be similar to that of most higher plants. The rDNA repeat size was 9.4 kbp in G. hirsutum and G. barbadense L., and 9.6 and 9.8 kbp in G. arboreum L. and G. herbaceum L., respectively. No intraspecific polymorphism was detected in the spacer. The presence of two SspI sites in G. arboreum and G. herbaceum and a single site in G. hirsutum and G. barbadense separated Old and New World cottons. The AFLP method produced a 10‐fold increase in the number of DNA bands per plant, compared with random amplified polymorphic DNA (RAPD) methods. The AFLP data assigned the species–genotypes into groups that corresponded with their origin and/or pedigree relationships.