bluuebunny/crossref_metadata_2025 huggingface dataset:
Cool‐Season Turfgrass Responses to Drought Stress1
Authors: Aronson L. J. , Gold A. J. , Hull R. J.
Published: July 2010

As the supply of water available for turf irrigation becomes limited, it is important to identify water‐efficient and drought‐tolerant turfgrasses. To establish the critical soil water potential at which cool‐season turfgrasses begin to experience drought stress, the growth and quality responses of Poa pratensis L. ‘Baron’, Lolium perenne L. ‘Yorktown II’, Festuca rubra var. commutata Gaud. ‘Jamestown’ and Festuca ovina var. duriuscula (L.) Koch ‘Tournament’ drought stress were compared in a greenhouse study. Evapotranspiration (ET) rates were measured using weighing lysimeters containing undisturbed cores of mature turf growing in a silt loams oil. Tensiometers and electrical resistance blocks were installed in a separate set of eight lysimeters containing L. perenne to determine the relationship between water loss due to ET and soil water potential. The ET rates of all grasses were unaffected until the soil water potential reached −50 to −80 kPa. During further soil water depletion, ET rates declined and drought stress symptoms became apparent. Leaf water potential of P. pratensis and L. perenne decreased by 50 to 75% when soil water potential declined to −80 kPa, while that of Festuca species remained relatively constant to a soil water potential of −400 kPa. Based on the parameters measured, P. pratensis and L. perenne exhibited a more rapid decline in ET rate, quality, and leaf growth under moisture stress than the two Festuca species, which demonstrated greater ability to thrive with limited soil moisture.
Nonstructural Carbohydrates and Nitrogen of Soybean Grown under Carbon Dioxide Enrichment
Authors: Allen L. H. , Vu J. C. V. , Valle R. R. , Boote K. J. , Jones P. H.
Published: July 2010

Carbon dioxide (CO2) concentration has been rising in the atmosphere for uver a century. This study was conducted to determine the effects of anticipated future levels of CO2 on nonstructural carbohydrates and N of soybean [Glycine max (L.) Merr. cv. Bragg]. Plants were grown at Gainesville, FL from seeding to maturity in six sunlit, controlled‐environment chambers that maintained CO2 at 330, 330, 450, 600, 800, and 800μmol (CO2) mol‐1 (air). Attached lysimeters contained Arredondo fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudult). Leaflet blades were sampled five times per day at 48 and 69 d after planting (DAP). At 48 DAP, average daytime starch conc. of leaflets increased with increasing CO2 from 85 g kg‐1 of dry wt at 330 μmol mol‐1 to 205 g kg‐1 at 800 μmol mol‐1. On each date, the daytime rate of starch accumulation combined over all CO2 treatments was 6 g kg‐1 h‐1. Specific leaf weight increased significantly throughout the day both at 48 (0.64 g m‐2 h‐1) and 69 DAP (0.29 g m‐2 h‐1). Total Kjeldahl N (TKN) conc., expressed on a g m‐2 basis, showed no change over the day. Total final dry wet increased 18, 34, and 54% at 450, 600, and 800 μmol mol‐1, respectively. The TKN harvested per plant increased 25, 26, and 45% in the 450, 600, and 800 μmol mo1‐1 CO2 treatments, respectively. Plants in the 450 μmol mol‐1 CO2 treatment partitioned more biomass to seed than the other CO2 treatments. With that exception, we saw no great differences among treatment partitioning at final harvest, and thus interpret the main effect of CO2 enrichment to be enhanced photoassimilation by soybean canopies while maintaining consistent allometric relationships of the plants.
Growth and Canopy Carbon Dioxide Exchange Rate of Spring Wheat as Affected by Nitrogen Status
Authors: Morgan Jack A.
Published: July 2010

Little information is currently available describing N nutritional effects on canopy CO2 exchange rate (CER). This field study was conducted to investigate how fertilizer N affects growth and photosynthesis of a dryland wheat (Tritlcum aestivum L.) stand in a Nunn clay loam (Aridic Argiustoll). Two tr eatments were imposed; an unfertilized (U) treatment, in which no fertilizer was applied, and an N‐fertilized (F) treatment, in which 100 kg fertilizer N ha‐1 was applied in the form of NH4NO3. Greater above ground growth and grain yield of fertilized wheat compared with unfertilized wheat were associated with greater CER and leaf area index throughout ontogeny and with greater crop growth rates early in development. Net assimilation rates, relative growth rates, and CER expressed on a leaf area basis either were unaffected by N or were reduced. However, greater leaf conductance to water vapor in the most recently fully expanded leaves of the F treatment during vegetative growth stages suggests that the upper leaves in the canopy may have had greater photosynthetic activity at that time compared with the U treatment. Utilization of intercepted photosynthetic photon flux density for CER by plants of the F treatment was equal to or greater than for plants of the U treatment despite more self‐shading in the former. Greater leaf photosynthetic capacity conferred by N fertilization apparently results in heavily shaded canopies using intercepted light as efficiently as open, better‐illuminated unfertilized canopies.
Sensitivity of Sorghum Grain Yield to Ontogenetic Changes in Respiration Coeffecients
Authors: McCree Keith J.
Published: July 2010

Only about 60% of the C taken up daily by crop photosynthesis contributes to yield. The remainder is lost during synthesis and maintenance. Previous estimates of losses have been based on the assumption that the synthesis efficiency (Yg) and the maintenance requirement per unit biomass (m) are constant. Recent controlled environment studies with sorghum [Sorghum bicolor (L.) Moench] have shown that after anthesis, the value of m decreases rapidly, while the value of Yg increases slowly. The consequences for grain yield are explored in this paper, using a new simulation model, McSorgSim. The model was first calibrated against field growth analysis data, then used to demonstrate possible advantages of selecting for high Ygand low m. To simulate the ontogenetic decrease in m for the plant as a whole, we assumed that the value of m for structural and storage tissue (stalk and panicle, including grain) was negligible in comparison with the value for metabolically active tissue (leaves and roots), and that the value of Yg for the storage and structural tissue was 18% higher than that of active tissue. Using these assumptions, simulations of daily C balance, standing biomass, and grain yield closely matched field data for sorghum growing in a warm, sunny, humid environment. The model indicated that reducing the night temperature by 10°C would increase the yield by only 4%. An assumption That values of m were uniform across plant organs led to a 35% underestimation of yield, while assuming that Yg also was uniform led to an additional decrease of 4%. If m for the panicle is already as low as these studies indicate, then it might not be possible to increase sorghum yield appreciably by selecting for a lower value.
Response of Alfalfa and Birdsfoot Trefoil to Shoot Removal and Root Anoxia
Authors: Barta A. L.
Published: July 2010

Shoot removal may accentuate potential plant injury when roots are under stress. Flood‐intolerant alfalfa (Medicago sativa L.) and flood‐tolerant birdsfoot trefoil (Lotus corniculatus L.) partition differing amounts of photoassimilate to roots during shoot regrowth, which may affect their ability to withstand stress. The objective of this study was to characterize plant response (growth and chemical composition) when root anoxia (severe hypoxia) and partial shoot removal were applied concurrently. Seedling plants (4–5 wk‐old) were grown in a growth chamber using nutrient solution. Alfalfa and trefoil roots were subjected to anoxia or O2 aeration (control) with shoots either clipped to 60‐ to 70‐mm stubble height or left unclipped. Root treatments were up to 5 d in duration. Alfalfa displayed greater damage (as measured by shoot dry matter accumulation) in response to root anoxia than did trefoil under both shoot treatments. Root anoxia significantly reduced root dry matter accumulation only in nonclipped plants, indicating that clipping had a more deleterious effect on root dry matter than did anoxia treatment. Both clipping and root anoxia had significant effects on root carbohydrates. A large increase in root sucrose concentration in response to anoxia was noted in alfalfa but not trefoil. Reducing sugar concentration declined in response to anoxia and clipping in alfalfa roots but only to clipping in trefoil roots. Root starch concentration increased in alfalfa and decreased in trefoil in response to root anoxia. There were no significant interactions between root aeration and shoot clipping in either species. Differential supply of photoassimilate did not appear to contribute to the differential tolerance to root anoxia displayed by these species. The data indicated that increased utilization of sugars may be important in trefoil's greater flooding tolerance.
Influence of Temperature on Heterosis for Maize Seedling Growth
Authors: Rood S. B. , Buzzell R. I. , MacDonald M. D.
Published: July 2010

Heterosis in crop plants may result partly from a superior ability of hybrids to tolerate environmental stress. The present study was conducted to investigate the influence of cool temperature on heterosis in maize (Zea mays L.). A four‐parent diallel including reciprocals, from maize inbreds A632, B73, CH607‐88, and CO109 was grown in controlled environment conditions under three temperature regimes: 20/10, 25/15, and 30/20°C (day/night). Leaf areas, heights and shoot dry weights were measured for growth analysis calculations. Potence ratios, representing the overall degrees of dominance, provided quantitative estimates of heterosis for the 12 hybrids. At all three harvests for all three temperatures, all hybrids had greater shoot dry weights and leaf areas and were taller than their parental inbreds. Consequently, potence ratios exceeded one for all parameters; considerable heterosis was observed in all hybrids at all temperatures. There were no general patterns of changes in potence ratios across the three temperatures. For example, mean potence ratios for leaf areas of the 12 hybrids over the three harvests were 16.7, 14.8, and 18.4, respectively, for the three temperature regimes. Thus, the level of heterosis in these hybrids was generally similar under favorable or unfavorable temperature conditions. This indicates that heterosis is not simply an ability of hybrids to better tolerate cool temperature stress. Rather, the hybrids from this group of elite inbreds displayed heterosis similarly under favorable or cool temperature conditions.
Influence of Cultivar and Seed Characteristics on Vertical Weight Displacement by Soybean Seedlings
Authors: Howle D. S. , Caviness C. E.
Published: July 2010

Emergence of soybean [Glycine max (L.) Merr.] seedlings often is erratic, especially when soil crusts form after heavy rains. Information is limited on traits that may affect the ability of soybean seedlings to emerge through compacted soils. The objectives of this study were to determine the effect of cultivars, position of pods on the plant, position of seeds in the pod, and number of seeds per pod on displacement of a 65‐g weight by soybean seedlings at 25°C. Vertical displacement of a 65‐g weight by individual seedlings in a controlled environment chamber was used to measure hypocotyl exertion force of individual seedlings. Seed size, weight, and density also were measured to determine the association of these seed traits with seedling weight displacement. Fifteen soybean cultivars of Group V maturity were grown under irrigated conditions on a Captina silt loam (fine‐silty, mixed, mesic Typic Fragiudult) at the Main Experiment Station, Fayetteville, AR. Seeds from these cultivars produced seedlings that had significantly different weight displacement values. Seeds produced on the upper one‐third of the plant produced seedlings that exhibited forces greater than those from the lower two‐thirds of the plants. Seedlings from seeds in two‐seeded pods had significantly higher weight displacement values than those from one‐seeded pods, and seeds from three‐seeded pods were intermediate in weight displacement. Cultivars differed significantly in mean seed size, weight, and density, but these seed parameters were not highly correlated with seedling weight displacement values. Coefficients of determination (r2) for the association between physical characteristics of seed and weight displacement by seedlings generally were <1.0%. Results indicate that genetic differences exist for seedling emergence potential in soybean, and that it may be possible to use this parameter to improve seedling emergence under compacted soil conditions.
Effects of Clipping Disposal, Nitrogen, and Growth Retardants on Thatch and Tiller Density in Zoysiagrass
Authors: Soper D. Z. , Dunn J. H. , Minner D. D. , Sleper D. A.
Published: July 2010

Accumulation of thatch is a cultural problem affecting managers of ‘Meyer’ zoysiagrass (Zoysia japonica Steud.). Research was undertaken to investigate the effects of clipping disposal, N fertilization, and growth retardants on thatch accumulation and resistance of plant tissue to decomposition. In a 2‐yr field study, clipping disposal (removed or left on plots); N fertilization (98.0 kg ha−1 yr−1); and the growth retardants mefluidide (N‐[2,4‐dimethyl‐5‐[[(trifluromethyl)‐sulfonyl]amino]phenyl]acetamide) applied twice each year at 0.4 and 0.8 kg a.i. ha 1, and flurprimidol (α‐(1‐methylethyl)‐α(4‐trifluromethoxy)phenyl)‐5‐pyrimidine‐methanol) applied at 1.7, and 2.2 kg a.i. ha−1 twice in each year were examined for their effects on thatch, tiller density, verdure, and stolon weight. Relative degradation of leaves and stolons was compared by in vitro digestion in a prepared cellulase solution. Returned clippings increased thatch by only 3.4% and decreased tiller density by 12% when N was applied. Nitrogen increased thatch and tiller density. Growth retardants did not affect thatch. Degradation of leaves (64%) by the cellulase solution exceeded that of stolons (60%). The reduction in tiller density associated with returned clippings may be due to shading from clippings in the turf canopy resulting in leaf etiolation and reduced tiller bud development. Leaf clippings contributed slightly to thatch accumulation, most likely due to their physical accumulation rather than indirect effects of N recycling. Both stolons and, to a lesser degree, leaves appear to contribute to thatch accumulation in Meyer zoysiagrass. Decreased use of N in the culture of Meyer zoysiagrass, within limits required for acceptable appearance, might help reduce thatch accumulation. Removal of clippings is not recommended for thatch control considering their small contribution to thatch cover and due to the benefit of recycled nutrients.
Genetic and Cytogenetic Variation in Plants Regenerated from Organogenic and Friable, Embryogenic Tissue Cultures of Maize
Authors: Armstrong C. L. , Phillips R. L.
Published: July 2010

Recent advances in maize(Zea mays L.) tissue culture methods permit reproducible establishment of rapid‐growing, friable, embryogenic (Type‐II) cultures from some genotypes. Although Type‐II cultures have replaced the more common Type‐I (relatively compact, organogenic) cultures for many applications, little information is available concerning somaclonal variation in plants regenerated from Type‐II cultures. This study was conducted to determine the relative frequency of genetic and cytogenetic variants in plants regenerated from Type‐I compared to Type‐II maize tissue cultures. Type‐I and Type‐II cultures were initiated from immature embryos of the inbred line A188, A188‐BC6 lines containing various genetic markers, and segregating progenies of an A188/B73 genetic background. Plants were regenerated 16 and 36 wk after culture initiation and were analyzed for pollen sterility, cytological abnormalities, and phenotypic variants in progeny generations. After 16 wk in culture, 33.3 and 20.8% of the regenerants from Type‐II and Type‐I cultures, respectively, possessed at least one abnormality. These values increased to 37.2 (Type‐II) and 24.2% (Type‐I) after 36 wk in culture. As expected, the frequency of chimeric plants was lower from Type‐II than from Type‐I cultures: however, culture age had a larger effect on the frequency of chimeric plants than culture type. Although reduced compared to Type‐I cultures, the frequency of chimerism in regenerants from Type‐II cultures was still quite high, ranging from 9.4 to 50.0% of the variant regenerants. The results demonstrate that genetic and cytogenetic abnormalities are frequently recovered in plants regenerated from both organogenic and friable, embryogenic maize tissue cultures.
Attributes of Tall Fescue Germplasm of Diverse Geographic Origin
Authors: Burner D. M. , Balasko J. A. , O'Brien P. M.
Published: July 2010

Foreign plant introductions (Pl) of tall rescue (Festuca arundinacea Schreb.) have not been adequately evaluated in the USA. Our objective was to determine whether variability in important agronomic characters exists among and within tall fescue accessions of different geographic origin. Twenty‐six foreign PI and three U.S. cultivars were compared in each of two space‐planted field experiments in different years and locations in West Virginia for water soluble carbohydrate concentration (WSC) of summer forage, yield, disease resistance, relative maturity, and winter injury. Accessions were grouped according to their geographic origin (three USA, 15 European, six Central Asian, and five Mediterranean). Data from the two experiments were combined because the same plant populations were evaluated in similarly designed studies. The USA and European groups yielded more first‐cat herbage (166 and 152 plant−1, respectively) than the Mediterranean group (110 g plant−1); they also yielded more regrowth herbage (51 g plant−1) than the Central Asian and Mediterranean groups (34 and 32 g plant−1, respectively). The European group was less diseased than the Central Asian and Mediterranean groups (P < 0.05). Geographic groups did not differ significantly in mean WSC, relative maturity, or winter injury. Substantial variation existed among accessions for all characters studied except winter injury. Among accessions, mean WSC ranged from 49 to 94 g kg−1, first‐cut dry matter yield ranged from 49 to 180 g plant−1, regrowth dry matter yield ranged from 11 to 58 g plant−1, and relative maturity ranged from 1.7 (boot) to 5.3 (half bloom). Accession means were not significantly different in winter injury score, but several North African and Israeli introductions, evaluated only in the first experiment, exhibited ≥42% winterkill. Genotypes markedly unadapted to the study environment were eliminated during the first winter, resulting in a population relatively homogeneous in winterhurdiness. ‘Kentucky 31’ was highest (P − 0.05) in WSC (94 g kg−1), but several European PI yielded more, were more disease resistant, or were earlier maturing. No foreign PI exceeded ‘Alta’ or ‘Fawn’ in yield (P < 0.05) although many had higher WSC. Central Asian and Mediterranean PI were generally undesirable in one or more characters. We conclude that breeding strategies for rapid development of tall fescue cultivars adapted to the temperate USA should concentrate on domestic cultivurs and European introductions as sources of superior germplasm.
Genetic Relationships among Soybean Plant Introductions for Resistance to Race 3 of Soybean Cyst Nematode
Authors: Rao‐Arelli A. P. , Anand S. C.
Published: July 2010

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a major pest of soybean, Glycine max L. Merr. Several plant introductions resistant to Race 3 have been identified, however the genetic relationships for resistance among them are not known. The F2 plants and F3 families from seven different crosses involving resistant parents were evaluated in the greenhouse to determine if the genes for resistance were identical or different from the genes in ‘Peking’ and/or PI 90763. Each seedling was inoculated with 1000 eggs and juveniles of SCN Race 3. Plant roots were washed after 30 d and white females enumerated. Based on the index of parasitism (IP) F2 plants and F3 families were categorized into resistant, segregating, or susceptible. The Chi‐square test was applied to determine goodness of fit between the observed and expected genetic ratios. Peking was found to have genes in common with PI 90763 and PI 438489B; whereas PI 90763 has genes in common with PI 438489BP, PI 404166, and PI 404198A. The cross between Peking and PI 88788 indicated segregation for one dominant and one recessive gene, and segregation in the cross PI 88788 × PI 438496B suggested two independent dominant genes. This information will assist soybean breeders in choosing additional resistant sources to SCN Race 3 in commercial cultivar development, thus providing a broader genetic base.
Changes in Viability, Germination, and Respiration of Freshly Harvested Soybean Seed During Development
Authors: Miles D. F. , TeKrony D. M. , Egli D. B.
Published: July 2010

As soybean [Glycine max (L.) Merr.] seeds develop and mature, they gradually desiccate to cause a switch in metabolic processes from a developmental to a germination phase. This investigation was conducted to determine when fresh (nondesiccated), immature soybean seeds acquire the ability to germinate and develop into normal seedlings. Soybean pods were detached from ‘DeSoto’ plants at four developmental stages ranging from full seed (first time the seed filled the locule) to yellow pod [physiological maturity (PM)] in 1981 to 1983. Freshly harvested seeds were immediately evaluated for seed moisture, dry seed weight, viability (radicle protrusion through the testa), germination (normal seedling development), and respiration. Seed and axis dry weight accumulation and moisture loss were nearly identical throughout development. Near maximum viability (93%) of freshly harvested seeds occurred when the seed first filled the locule (35% of final dry seed weight); however, maximum germination (development of normal seedlings) did not occur until maximum accumulation of dry seed weight (PM). Respiration during germination of fresh seed harvested before PM declined prior to radicle emergence without a concomitant decrease in seed moisture, followed by an increase in respiration typical of a germinating seed. Contrary to previous reports, freshly harvested immature soybean seeds did not need a desiccation period prior to expression of maximum viability and normal seedling development.
Analysis for Tannin Concentration in Sericea Lespedeza by Near Infrared Reflectance Spectroscopy
Authors: Windham W. R. , Fales S. L. , Hoveland C. S.
Published: July 2010

Near infrared reflectance spectroscopy (NIRS) has become widely accepted for the analysis of forage quality parameters. However, this technology has not been tested adequately for its capacity to analyze forages for antiquality parameters. Our objectives were to evaluate the utility of NIRS to determine the tannin concentration of sericea lespedeza [Lespedeza cuneata (Dum.‐Cours.) G. Don.] and to quantify the seasonal tannin fluctuations of various high‐ and low‐tannin entries. We assayed tannin concentration of nine sericea entries grown on a Cecil coarse sandy loam (clayey, kaolinitic, thermic Typic Hapludult) near Athens, GA, and harvested in June, August, and October in each of 3 yr. Calibration equations were obtained by regression of the vanillin‐HCl tannin values on NIR spectra from 100 randomly selected samples using a scanning NIR monochromator spectro‐computer system. Five wavelengths were required to derive the best equation with a standard error of calibration of 14.0 g kg−1 dry matter (DM). Analysis of the remaining samples gave a standard error of analysis of 15.0 g kg−1 DM, which was similar to the standard of the reference method in our laboratory (SE = 12.1 kg−1 DM). Differences in tannin concentration of sericea lespedesa were due to an entry ✕ season ✕ year interaction (P < 0.0001). Tannin concentrations increased in summer but returned to lower levels in autumn. These fluctuations were greater in the high‐ than low‐tannin entries (P < 0.05). We conclude that NIRS can analyze the tannin concentration of high‐ and low‐tannin sericea lespedeza with an accuracy similar to the reference method. Use of NIPS should allow breeders to screen larger numbers of sericea lespedeza lines than would otherwise be possible.
An Intermittent Aeroponics System
Authors: Peterson Lloyd A. , Krueger Armand R.
Published: July 2010

An intermittent aeroponic system was designed and tested for potential use in plant growth studies. Cucumber (Cucumis sativus L.) were grown in the system from the cotyledon stage to flowering and fruiting within 40 d on a misting schedule of 7 s at 10‐min intervals with about one half strength Hoagland's solution. The root environment was controlled at 20 ± 1.1 °C; however, other temperatures can be established. Root growth was rapid with good branching and root hair development. The proposed plant growth system provides the benefits of easy access to the root system and control of the misting solution composition as related to elemental concentration or to an application of a plant growth regulator at different stages in the developing root. It may also provide a system for testing short‐term water stress in relation to plant development. The system as described has been running continuously for 32 wk without an operational problem.
Application of an Optimization Model to Multi‐Trait Selection Programs
Authors: Johnson Blaine , Gardner C. O. , Wrede K. C.
Published: July 2010

Simultaneous multi‐trait selection involves making many separate decisions which ultimately reflect the total value of each genotype being considered. A linear index is frequently used to simplify these decisions. However, use of traditional selection indices has required knowledge of the relative genetic merit of each trait. The objective of this investigation was to devise a method which applied breeders could utilize in determining appropriate relative values for the genetic merits. A procedure was developed whereby approximate values could be derived from a ranking of genotypes. The procedure requires a subjective ranking made by the breeder based on simultaneous consideration of the traits of interest. The utility of the procedure in applied breeding situations was tested. The technique was used to determine the relative merit of each of three traits, grain yield, moisture content of grain at harvest, and percent standing plants at harvest, in six sets of selected and ranked S2 and S3 families of maize. The selections and rankings were subjectively made by two experienced maize breeders. The two breeders were unable to numerically express acceptable relative merits, or relative weights, for the three traits prior to the solution of the problem. They were able to state general selection goals and to subjectively rank the families accordingly. The two breeders had basic philosophical differences in selection goals and these differences were detected by the weights derived from the breeders' respective rankings. The method provides flexibility which is lacking in other procedures and has potential utility in applied breeding programs as a management and operational tool.
Forage Quality and Digestion Kinetics of Switchgrass Herbage and Morphological Components
Authors: Twidwell E. K. , Johnson K. D. , Cherney J. H. , Volenec J. J.
Published: July 2010

As switchgrass (Panicum virgatum L.) matures, whole plant nutritive value declines. In field studies, ‘Cave‐In‐Rock’, ‘Pathfinder’, and ‘Trailblazer’ switchgrass were seeded into a Blount silt loam soil (fine, illitic, mesic Aeric Ochraqualf) to determine the interaction between morphological components and maturation and its impact on forage quality. Herbage was initially harvested when the flag leaf was just visible with subsequent harvests occurring 14 and 28 d later. Cave‐In‐Rock had higher (25 g kg−1) in vitro dry matter disappearance (IVDMD) and lower (35 g kg−1) neutral detergent fiber (NDF) concentrations than the other cultivars (P < 0.05). Leaf blades, which comprised 47% of total forage at the first harvest and 26% at the last harvest, were highest in N concentration, IVDMD, and extent of NDF digestion for all harvest dates. Leaf sheaths and stems had similar N concentrations, but for IVDMD, NDF, lignin, and extent of cell wall digestion, leaf sheath values were intermediate between blades and stems. Lignin concentration of stems between the first and last harvest increased 38.8 g kg−1, while stem IVDMD and extent of stem NDF digestion declined 210 g kg−1 and 228 g kg−1 NDF, respectively. No significant whole plant cultivar differences were found for either rate or 96‐h extent of NDF digestion (P > 0.05). The in vitro rate constant for stem NDF declined 0.024 h−1 with maturation (P < 0.05), while leaf blade and sheath rate constants did not change. These results indicate that changes in the proportion and composition of the stem fraction and composition of the sheath fraction are the major factors causing a decline in switchgrass herbage quality and rate of NDF digestion with maturation.
Relationships between Laboratory Germination Tests and Field Emergence of Maize Inbreds
Authors: Martin B. A. , Smith O. S. , O'Neil M.
Published: July 2010

In the USA and Europe, maize (Zea mays L.) is often planted into soils that are or become cold and wet resulting in reduced field emergence, poor stands, and lower economic yields. This study was conducted to determine the relative merits of two germination tests, the cold and soak tests, for prediction of field emergence when soil temperatures are suboptimal for germination. The effects of initial seed moisture on field emergence were also investigated. Field emergence of 48 maize inbred lines was measured in eight locations in 1986 and 1987. The seeds of each inbred were also cold and soak tested. Seeds taken directly from conditioned storage and seeds dried to 80 g kg−1 moisture were used in these studies. In 1986, the cold and soak test were equally correlated with field emergence r = 0.43** (significant at the 0.01 level of probability) and 0.40** respectively. In 1987, the cold test was more highly correlated with field emergence (r = 0.74**) than the soak test (r = 0.43**). These correlations between laboratory germination tests and field emergence were affected by both location and year. Drying seeds to 80 g kg−1 moisture resulted in an overall 5% decrease in field emergence in both years. There was a significant inbred line‐by‐year interaction, but only one inbred was significantly affected in both years. The value of these germination tests as a tool to aid selection was also investigated and both tests were equally accurate (60% agreement) at predicting those inbreds with field emergence in the lower 30% in both years. The soak test may be considered a rapid, inexpensive, and effective selection tool for elimination of those inbreds with poor field emergence, however, the cold test was superior for prediction of the field emergence of a wide range of inbred lines in a number of environments.
Analysis of Differences in Sink Activity among Soybean Genotypes Based on Dry Matter Accumulation Rates per Unit Seedcoat Area
Authors: Hanson W. D.
Published: July 2010

This study tested the hypothesis that genetic differences for sink activity, a component of sink strength, affect assimilate flux to seeds in soybean [Glycine max (L.) Merr.]. Dry matter accumulation rate per unit seedcoat area (SDMAR) was selected to investigate sink activity. The capacity to maintain high SDMAR under limiting and nonlimiting assimilate availability was used to identify those genotypes having high sink activity. The ellipsoid served as the model to determine seedcoat area and seed volume. Four soybean genotypes differing in accumulation rates and 24 genotypes reflecting divergent selection for seed yield were evaluated in the greenhouse under three treatments: control, side leaflets removed, and pods removed except for selected pods. Highly significant mean squares for SDMAR were found for genotypes and for the genotype‐by‐treatment interaction. The SDMARs for genotypes with high and with low SDMAR were proportionately affected under treatments that decreased or increased SDMAR. High SDMAR imparted no advantage for maintaining assimilate utilization under limiting assimilates. Further, genotypes selected for high and for low seed yields had similar SDMARs. The results do not support the concept of major differences in sink activity among genotypes. The pod‐removed treatment increased SDMAR 16% and reduced the increase in seed dry weight per unit volume associated with maturation, or it delayed the maturation process. High yielding genotypes had lower dry weight per seed volume than low yielding genotypes. The capacity to maintain sink activity may be a component for high seed yield.
A Procedure for One Cycle of Recurrent Selection per Year with Spring‐Sown Small Grains
Authors: Frey K. J. , McFerson J. K. , Branson C. V.
Published: July 2010

The objective was to combine a set of crossing and evaluation techniques into a regime that permits a breeder to conduct one cycle of recurrent selection for protein or grain yield of oats (Avena sativa L.) per year. Parental strains are crossed in the greenhouse during September to December, S0 plants are propagated in the greenhouse during December to March, S0.1 lines are evaluated in a replicated multilocation experiment in the field during April to July, and data summary and selection of parental lines for a new cycle occur during August. The schedule is repeated for each cycle. Over three cycles, the gain per cycle (and per year) was 4.7% for protein yield and 5.4% for grain yield. Techniques employed to permit completion of a cycle of recurrent selection in 1 year were: (i) approach method of crossing, (ii) evaluating S0.1 lines, (iii) hill plots for field evaluation, (iv) infrared analyzer for N determinations, and (v) computer data analyses and line selection.
Pollen Selection for Heat Tolerance in Cotton
Authors: Rodriguez‐Garay Benjamin , Barrow Jerry R.
Published: July 2010

Pollen from cotton (Gossypium hirsutum L.) cultivars, which demonstrate heat tolerance in the field, generally express higher fertility after heat treatment than pollen from heat sensitive cultivars. The objective of this study was to determine, if pollen could be heat treated to eliminate all but those grains with genetic heat tolerance. Genes for heat tolerance could then be selected in the pollen and effectively transferred by the backcross method. A highly heat tolerant breeding line, 7456, of G. barbadense L. was used as the donor parent and ‘Paymaster 404’, a heat sensitive cultivar, as the recurrent parent and all crosses were made with pollen treated 15 h at 35 °C to generate F1, F2 and first and second backcross populations. Increased heat tolerance, as measured by fertile pollen after heat treatment, was observed in plants from all populations. Similar heat tolerance patterns were observed in the parents, F1, F2, and first backcross populations, when plants were grown to maturity at high temperatures in a growth chamber. Pollen selection through heat treatment allows screening for large numbers of genetic combinations in pollen and may be a valuable method of breeding for heat tolerance and possibly other stress tolerance characteristics.
Non‐Nodulating Mutants in Common Bean
Authors: Davis J. H. C. , Giller K. E. , Kipe‐nolt J. , Awah M.
Published: July 2010

Estimates of nitrogen fixation by common bean (Phaseolus vulgaris L.) have been made using non‐nodulating soybean or other nonfixing plant species to measure soil nitrogen because non‐nodulating bean lines are not available. Such lines are also needed for studies on the genetic control of nodulation. The objective of this study was to obtain (using induced matagenesis) nodulation mutants of the bean lines ‘RIZ 30’ and ‘RIZ 36’. One hundred and twelve nonnodulated plants were identified in the M2 generation following treatment of imbibed seeds with 0.08 M ethyl methane sulfonate for 4 h. Screening was carried out in perlite with a nitrogen‐free nutrient solution, and seeds were inoculated with a mixture of Rhizobium strains CIAT 632 and CIAT 899 before emergence. Plants were uprooted 3 wk after planting, and those without nodules were transferred to soil for seed production. The absence of nodulation by eight lines was confirmed in the M3 and M4 generations following inoculation with several other strains of Rhizobium, and in the M5 generation two mutant lines were evaluated in soil. Seed set in these lines is poor, though improved by applying nitrogen.
Distribution of Sugar and Soluble Solids in the Maize Stalk
Authors: Widstrom N. W. , Carr M. E. , Bagby M. O. , Black L. T.
Published: July 2010

Limited worldwide energy sources have encouraged the search for energy alternatives such as stalk sugar in maize, Zea Mays L. Information on the distribution and amount of sugars and soluble solids found in maize stalks will be important if the maize plant is to be exploited for its total energy production. The objective of this study was to determine the distribution of soluble solids in the stalks of three maize hybrids. Three field plantings of five replicates were made at 4‐wk intervals in 1981,1982, and 1983. Juice was sampled from each of the first ten internodes of two plants from each plot and a Brix reading taken by hand‐held refractometer. In 1983, internode samples from each node in each plot were bulked and analyzed for sugar content using High Performance Liquid Chromotography (HPLC). Significant variation for soluble solids occurred among years, hybrids, and nodes. An older hybrid, developed for the South, had stalks that tended to increase in soluble solids concentration from bottom to the top of the plant. Two more recently developed hybrids decreased in soluble solids concentration from soil level upward toward the ear node, but increased from the ear node upward. The change or difference in pattern of soluble solids gradients for the more recently developed hybrids was attributed in part to selection for increased resistance to stalk rot, which is positively correlated with sugar content.
Photosynthesis and Stomatal Conductance of Selected Root Crops as Related to Leaf Age
Authors: Bhagsari Ajmer S.
Published: July 2010

Single leaf net photosynthesis (Pn), canopy photosynthesis (CPn) and stomatal conductance of sweet potato (lpomoea batatas L.), cassava (Manihot esculenta Crantz) and yam (Dioscorea alata) were determined under field conditions in full sunlight (above 1500 gmol m−2s−1) between 1100 and 1500 h EST during 1983 and 1984. Canopy photosynthesis was determined with a portable plexiglass photosynthesis chamber in a closed system under ambient conditions. Single leaf net photosynthesis was determined at 30± 2 °C by enclosing attached fully mature leaves in an acrylic plastic chamber in an open system. The mean Pn for sweet potato, cassava, and yam were 1.10, 0.70, and 0,30 mg CO2 m−2s −1, respectively. Mean CPn rates, expressed on leaf area basis, for sweet potato, cassava, and yam were 0.18, 0.38, and 0.17 mg CO2 m−2s−2, respectively. Abaxial stomatal conductances for cassava and sweet potato were almost similar, but both were three to five times higher than for yam. Adaxial stomatal conductance ranged from 0.007 to 0.010 m s&1 for sweet potato and was less than 0.001 m s& for both yam and cassava, indicating the lack of stomata or their poor development on the adaxial surface. With increase in leaf age from about 20 to 60 d, both Pn and stomatal conductance declined faster in sweet potato than in cassava and yam. Single leaf photosynthetic rates were higher for sweet potato than cassava. However, CPn comparisons involving complete plant foliage indicated that photosynthetic efficiency of cassava was superior to that of both sweet potato and yam. Cassava also partitioned more photosynthate to storage roots than the other two species. The lesser decline in cassava Pn with aging (and consequently of CPn) than sweet potato partially explains why cassava productivity is similar to sweet potato even when sweet potato Pn is 50.0% more than that of cassava.
Evaluation of S2 Maize Lines Reproduced for Several Generations by Random Mating within Lines. I. Comparisons between the Original and Maintained S2 Lines
Authors: Carlone M. R. , Russell W. A.
Published: July 2010

Most parents used in single‐cross maize (Zea mays L.) hybrid seed production are highly inbred lines that have been developed through many generations of selfing and evaluation. Many times, lines with good combining ability are identified in the first few generations of inbreeding, but after additional generations of selfing they become less vigorous and too weak (Le., reduced seed yield and pollen production) to be economically used. One way to overcome the problem of severe inbreeding depression and reduced vigor is to use lines that have been only partly inbred and are maintained by random‐mating within lines (sib‐mating). The primary objective of this study was to compare original S2 lines with their maintained S2‐line counterparts to determine if the genetic integrity was maintained after several generations of sib‐mating. We evaluated the performance of 14 original S2 maize lines and their progenies reproduced by sib‐mating for several generations There were 14 original S2 lines, each S2 line maintained by using 10 plants per generation for six generations, each S2 line maintained by using 20 plants per generation for six generations, and four lines were maintained by using mild selection for five generations. The S2 lines were evaluated in a randomized complete‐block design in four environments. Significant (P < 0.05) or highly significant (P < 0.01) differences were found among S2‐line groups for all traits except kernel row number and ear length. When compared as groups, the S2 lines maintained by using 10 and 20 plants yielded 3.66 and 3.63 Mg ha−1, respectively, significantly less than did the original S2 lines (3.83 Mg ha−1). Conversely, the S2 lines maintained by using mild selection yielded the same as their original S2‐line group. Individual comparisons between each original SI line and its maintained S2‐line counterpart showed that significant changes in the maintained S2 lines occurred in both the positive and negative directions for 50% of the traits. The S2 lines maintained by using 10 plants per generation tended to be less stable than if they were maintained by using 20 plants when compared with their original S2‐line counterparts. Also, data from electrophoretic assays showed results similar to those observed in field evaluation. It was concluded that the genetic integrity of the original S2 lines was not maintained by using sample sizes of 10 or 20 plants for grain yield. The changes in the lines' performances were small, however, compared with changes that would have occurred if the lines had been further inbred by conventional pedigree methods.
Agronomic Performance of Trianzine‐Resistant and Susceptible Reciprocal Spring Canola Hybrids
Authors: Beversdorf W. D. , Hume D. J. , Daonnelly‐Vanderloo M. J.
Published: July 2010

Triazine‐resistant (TR) spring rapeseed (canola) (Brussica napus L.) cultivars have been developed that permit selective chemical control of weeds but TR cultivars generally yield 20 to 30% less than triazine‐susceptible (TS) cultivars. This lower yield in TR cultivars has been attributed to impaired electron flow between photosystems I1 and I. The objective of this experiment was to use reciprocal TR and TS hybrids to assess the effects of the TR trait in the same nuclear genetic background. The TR canola cv. OAC Triton was handcrossed with two TS cv., Topas and Hanna, to create reciprocal hybrids from each cross. The TR trait was cytoplasmically inherited so reciprocal hybrids were either TR or TS. Each cultivar plus the four hybrids were field tested in 1984 and 1985. The TR hybrids exhibited 21 and 25% lower yields than TS hybrids, flowered an average of 2 d later and had 8% lower mature plant heights. Days to maturity in the reciprocal hybrids were the same. The two TS hybrids exhibited an average of 14% high‐parent heterosis for seed yield (2.96 vs. 2.60 Mg ha−1). The TR hybrids yielded less than midparent averages and not significantly more than the TR parent (2.27 vs. 2.11 Mg ha−1). The results suggest that TR hybrids will not perform well unless TR parental genotypes with more normal photosynthetic capabilities are found.
DNA Homology Group and the Identity of Bradyrhizobial Strains Producing Rhizobitoxine‐Induced Foliar Chlorosis on Soybean
Authors: Devine T. E. , O'Neill J. J. , Kuykendall L. D.
Published: July 2010

A distinctive foliar chlorosis of soybean, Glycine max (L.) Merr., has been traced to nodulation by certain strains of bradyrhizobia that produce the substance rhizobitoxine in the root nodules. Strains of Badyrhyzobiurn nodulating soybean have been classified into three groups by relative DNA homology. To define the possible relationship between chlorosis induction and DNA homology group, 25 bradyrhizobial strains identified by DNA homology group were tested for chlorosis induction on the chlorosis susceptible soybean Line N53‐ 3494. Stationary‐phase broth cultures of bacterial strains were inoculated onto surface‐sterilized seeds planted in vermiculite in Leonard jars. Plants were scored visually for expression of rhizobitoxineinduced foliar chlorosis 35 d after planting. None of the 16 strains in DNA homology Groups 1 and la produced rhizobitoxine‐induced foliar chlorosis. Only strains in DNA homology Group 2 induced chlorosis, but not all of the strains of this group induced chlorosis. Five of the nine strains examined in Group 2 produced chlorosis symptoms in this test. Of the four remaining strains one was previously reported by another investigator to produce mild chlorosis symptoms and another strain was reported to produce rhizobitoxine in vitro. These results indicate that bradyrhizobial strains isolated from soybean in the USA that induce foliar chlorosis are of a distinct DNA group.
Presence of the Transposable Element Uq in Maize Breeding Material
Authors: Cormack Jean B. , Cox D. F. , Peterson Peter A.
Published: July 2010

The insertion and excision of transposable elements often lead to alterations in the base pair sequence of a gene. This could contribute to polymorphism and genetic variation in maize (Zea mays L.) germplasm. The objective of this experiment was to establish whether or not breeding material that showed genetic variability contained the transposable element Uq. Populations and inbred lines were crossed with a genetic tester containing c‐ruq, the receptor for Uq. Populations that contained the element Uq include Iowa Stiff Stalk Synthetic, Burrs White, Hays Golden, Iowa Long Ear, Lancaster, Kolkmeier, and Bsll. The inbred I159 also contained Uq. This study screened for only one of nine genetically characterized elements. The absence of Uq does not indicate the absence of other known or unknown elements.