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Soybean seed protein is deficient in the essential sulfur containing amino acids, methionine and cysteine. Naeve and Shibles (2540–2551) studied sulfur mobilization by pulsing hydroponic soybean plants with 35S labeled SO4 at several discrete stages during the reproductive phase of development. Sequential harvest of plants indicated where and how S is stored and mobilized during reproduction. This study demonstrates that developing soybean seeds are dependant on S that has been mobilized from other plant tissues. Increasing storage of sulfur in vegetative tissues may result in soybean plants that produce seed with higher concentrations of S-amino acids.
Amino Acids and Ureides in Chickpea
The metabolic products of N fixation in a legume can be amides (asparagine, glutamine) or ureides (allantoin and allantoic acid), which are then exported to the shoot via the xylem. The objectives of Thavarajah et al. (2497–2502) were to determine the free amino acids and ureides and to quantify differences in N2 fixation among chickpea cultivars in the field by 15N natural abundance. Two chickpea cultivars had significantly higher N2 fixation compared with the other cultivars. On the basis of the concentration of both types of N product found in the shoot, chickpea should be classified as both an amide and ureide exporter.
Grazing Evaluation of Improved Big Bluestems
Limited information is available concerning livestock response to improvements in forage yield and digestibility. Mitchell et al. (2288–2292) compared the big bluestem ‘Pawnee’ and ‘Kaw’ to ‘Pawnee C3’ and ‘Kaw C3’, the parent populations improved through three cycles of selection for increased yield and digestibility. Averaged over the 3 yr, Pawnee C3 and Kaw C3 produced 16 and 7% greater average daily gain than their parent populations. Pawnee C3 pastures produced 14% more livestock gain per hectare than Pawnee pastures, and Kaw C3 pastures produced 5% more livestock gain per hectare than Kaw pastures. Pawnee C3 and Kaw C3, released as ‘Bonanza’ for Plant Hardiness Zone 5 and ‘Goldmine’ for Plant Hardiness Zone 6, represent the first big bluestem cultivars developed for increased animal performance by increasing forage yield and digestibility.
Targeting Cultivars onto Rice Growing Environments
Genotype (G) and genotype x environment (GE) interaction should be considered when recommending a cultivar for a specific environment. Samonte et al. (2414–2424) demonstrated the interpretation of multienvironment rice grain-yield data using additive main effects and multiplicative interactions (AMMI) model and GGE biplot analyses. The magnitude and significance of GE interaction effects and its principal components were estimated, and stability and adaptability of cultivars were assessed through AMMI model analysis, while the relative performance of cultivars at specific or different environments were compared, and ideal cultivars and test locations were identified through GGE biplot analyses. The highest yielding cultivar in each megaenvironment was identified through both AMMI model and GGE biplot analyses.
Temperature, Nitrogen, and Light Effects on Bermudagrass
Currently, very little research data are available concerning the combined effects of temperature and light on the developmental morphology of ‘Tifdwarf’ bermudagrass. Stanford et al. (2491–2496) conducted growth chamber experiments at three different day/night temperature regimes, three N application rates, and three photosynthetic photon flux density (PPFD) levels. Results showed a positive correlation between phyllochron and day/night temperature. Increasing N increased internode length, leaf length, and shoot weight. After exposure to daytime temperatures of 27°C or less and a PPFD of 600 µmol m–2 s–1 or less, the growth form of Tifdwarf bermudagrass changed dramatically, resulting in plants with longer internode spacing and longer leaves.
Water Use Efficiency in Rice
Drought is the major constraint for productivity in agricultural crops, including rice. Enhancing the water use efficiency (WUE) is a plausible approach to improve drought tolerance in rice. Impa et al. (2517–2522) showed that carbon isotope discrimination (
13C) is a powerful estimate of season-long WUE and is a stable trait across environments. The stable isotope approach can therefore be effectively used in exploiting the variability in WUE for crop improvement.
Genome Mapping of Dioecy in Texas Bluegrass
Dioecy promotes cross-pollination and would be of value in the breeding and improvement of economically important self-pollinated crops; however, little has been done to investigate dioecy in the Poaceae. Renganayaki et al. (2529–2539) constructed an AFLP-based linkage map of dioecious Texas bluegrass. More than 75% of the Texas bluegrass genome was covered in the map. In addition, two male-specific AFLP markers mapped to a genomic region on the paternal map. This genome map and the male-specific markers provide tools for conducting marker-assisted breeding and studying the genetics of dioecy in Texas bluegrass.
Tillage Effects on Corn Yield and Labor and Fuel Inputs
Lithourgidis et al. (2523–2528) investigated the effects of three tillage systems on corn emergence and silage yield and on wheat grain yield in a double cropping sequence. Labor and fuel consumption required for corn production was calculated. The results indicate that there was no significant effect of conservation tillage practices on corn and wheat yield compared with conventional tillage, whereas these practices provided significant saving in labor and fuel consumption required for corn production. Furthermore, the level of soil moisture at sowing may affect corn emergence and establishment, particularly with no-tillage.
Differential Adaptation of Wheat to High Temperature Environments
Understanding the target environments and G x E interaction is essential in plant breeding. Lillemo et al. (2443–2453) analyzed differential adaptation of bread wheat to various heat-stressed environments around the world by cumulative cluster analysis of CIMMYT's High Temperature Wheat Yield Trial. A clear distinction was observed between sites with heat stress and more temperate locations, and between heat environments with high temperature throughout the season and sites with terminal heat stress. Specific adaptation of genotypes to the various heat environments was apparent, but lines were identified that performed well across all types of heat stress.
Timothy Leaf and Stem Fiber Traits
Improved dry matter digestibility of herbage can be caused by changes in fiber composition of leaves and/or stems and/or to changes in the proportion of leaves and stem in the herbage. Claessens et al. (2425–2429) applied divergent selection for the ratio of acid detergent lignin (ADL) to cellulose (CEL) in timothy. Selection for low values of ADL/CEL reduced ADL and neutral detergent fiber concentrations in stems and increased the in vitro true digestibility of stems but had no consistent direct effects on plant morphology or leaf characteristics. Thus, the observed changes in the overall herbage digestibility due to selection for this ratio can be attributed mainly to modification of stem digestibility.
Tall Fescue Seed Production
Effective weed control is a critical component of high quality grass seed production systems. Recent transition by Oregon tall fescue seed growers from field burning to mechanical methods of managing postharvest residues greatly increased reliance on herbicides. Mueller-Warrant and Rosato (2614–2628) evaluated the performance of promising herbicide and residue management treatments reapplied to the same plots during four growing seasons. Most treatments effectively controlled volunteer tall fescue seedlings, but had varying impact on crop yield. Proliferation of the perennial weed roughstalk bluegrass in some treatments became a major cause of yield loss by the study's termination.
Heterosis and Breeding Strategies for Maize in Acid Soils
Breeding programs have produced maize populations adapted to tropical acidic soils. Welcker et al. (2405–2413) evaluated the potential of these populations to generate new breeding germplasm by a series of diallel crosses, including six acid soil-tolerant and five susceptible populations, on acidic, Al-toxic soils in Guadeloupe, Cameroon, and Colombia. Heterosis markedly increased grain yield (32%). Genes had strong additive effects on performance of the crosses. The development of variety crosses between tolerant populations of various origins could be used to increase the yields of maize grown on acid soils.
Barley Gene Confers Salt Tolerance in Oat
A major cause of oat yield loss worldwide is osmotic stress due to salinity. Oat was genetically transformed with barley HVA1 gene using Biolistic bombardment of differentiated multimeristems from shoot apex. Stable integration and expression of transgene was confirmed in R3 progenies. Compared with nontransgenic control, transgenic lines exhibited significant increase tolerance under 200 mM NaCl, and greater growth and yield performance (Oraby et al., 2218–2227). The results suggest that expression of barley HVA1 gene in transgenic plants can improve agronomic performance and reduce yield loss under osmotic stress.
Rapid Prediction of Total Dietary Fiber in Barley
High dietary fiber is undesirable in barley used for brewing and animal feed and desirable in barley used for food production. Because total dietary fiber (TDF) is extremely laborious to measure, Kays et al. (2307–2311) used near-infrared spectroscopy as a rapid method of predicting dietary fiber in barley cultivars. Near-infrared reflectance spectroscopy was an accurate method for the termination of TDF in ground barley samples. Near-infrared transmission spectroscopy of polished barley grains is less accurate, but appears to provide sufficient accuracy for selecting or rejecting high dietary fiber cultivars from large numbers of progeny and requires less sample preparation.
Whole-Farm Perspectives of Grassland Agriculture
Nutrient cycling in grassland agriculture is fundamentally different from that in row-crop agriculture. Rotz et al. (2139–2159) review the principles of nutrient cycling in grassland agriculture, discuss examples of grassland farming systems research, and demonstrate the usefulness of whole-farm simulation for integrating economic and environmental components. In many areas of North America and Europe, grasslands are managed along with annual crops such as maize, forming very complex livestock farming systems. A whole-farm approach is needed to develop more efficient nutrient management strategies that reduce nutrient losses to the environment while maintaining profitable production systems.
Cuphea Yield in the Corn Belt
In temperate regions, cuphea (Cuphea viscosissima Jacq.) seeds may substitute for tropical palm seeds for production of medium chain length fatty acids, but the extent of latitudinal adaptation of cuphea is not known. Forcella et al. (2195–2202) established planting date trials at seven experiment stations from southwestern Iowa to northwestern Minnesota (41–49° N latitude) in 2002 and 2003. Cuphea was able to produce high biomasses along most of this transect, but high seed, oil, and capric acid yields occurred only above 44° N latitude. Currently available cuphea varieties (e.g., ‘PSR23’) appear adapted only for northern states such as Minnesota.
Wind Effect on Corn Leaf Azimuth
Stalk breakage, greensnap, in pretassel corn increases when leaf azimuths are parallel to extreme thunderstorm winds, yet wind effect on leaf azimuth is unknown. Elmore et al. (2598–2604) recorded leaf azimuths north of east–west windbreaks for both wind sheltered and unsheltered plants. Early-season wind altered leaf placement. In a spring with strong winds, leaves of sheltered plants were oriented in north–south patterns, while unsheltered plants had few leaves pointing southward. Understanding the critical role early-season wind has on leaf azimuth may lead to improved management programs and increased tolerance to greensnap.
Plantain Freezing Tolerance
Use of narrow-leaf plantain (Plantago lanceolata L.) as a forage crop in the northeastern USA has been limited because of its poor winter survival. Skinner (2330–2336) compared growth rates at near-freezing temperatures and freezing survival of three cultivars to determine if reducing fall growth could improve freezing tolerance. However, reduced growth at low temperature did not reduce freezing injury. In fact, the cultivar with the greatest shoot growth rate at low temperature also had the greatest survival after freezing to –12°C. This research suggests that cultivars can be developed with improved freezing tolerance without sacrificing fall productivity.
Water Stress Effects on Cotton Photosynthesis
Water stress may decrease photosynthesis by increasing both diffusional (e.g., stomatal) and nondiffusional (biochemical) limitations to CO2 assimilation. Ennahli and Earl (2374–2382) used combined measurements of leaf gas exchange and chlorophyll fluorescence to differentiate between these two types of limitations in cotton leaves. Mild water stress increased diffusional limitations, but severe water stress also increased nondiffusional limitations, which were not reversed completely even 48 h after relief of the stress, indicating lasting injury at the level of the chloroplast. Combined gas exchange–fluorescence measurements can provide meaningful information about limitations to photosynthesis under conditions where gas exchange techniques alone are unreliable.
Nutritive Value and Morphology of Bothriochloa spp
Introduced forages offer alternatives to traditional cropping systems in the semiarid Texas High Plains, but effects of irrigation on nutritive value are not well known. Philipp et al. (2258–2268) surface drip-irrigated three old world bluestem [Bothriochloa caucasica (Trin.) C.E. Hubbard, ischaemum (L.) Keng., and bladhii (Retz) S.T. Blake)] and showed that irrigation likely affected nutritive value through effects on plant morphology and physiological age. Dry matter digestibility (DMD) of all species was higher at a low irrigation level than at dryland, medium, or high irrigation levels. Bothriochloa bladhii was higher in crude protein than B. ischaemum and B. caucasica during the growing season. In all species, total nonstructural carbohydrates and DMD declined, while neutral detergent fiber and acid detergent fiber increased with increasing irrigation.
Cotton Yield Potential and Suppression Caused by the Southern Root-Knot Nematode
Davis and May (2312–2317) measured the yield potential and percentage loss to the southern root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, in 12 cotton (Gossypium hirsutum L.) genotypes in 2002 and 2003. Percentage yield suppression was not consistently related to genotype, so cultivar selection is unlikely to be useful for minimizing nematode damage. However, the percentage yield suppression increased as yield potential increased regardless of genotype. Therefore, nematode management becomes increasingly important as yield potential increases.
Genetic Relationships of the RWA Resistance Genes
Resistant wheat cultivars provide good control of Russian wheat aphid (RWA), and genetic characterization is critical to the continual use of resistance genes. In this study, Liu et al. (2273–2280) report the chromosome location and the genetic relationships of the RWA resistance genes Dn1, Dn2, Dn5, Dn6, Dnx, and several uncharacterized Dn genes by molecular mapping and allelism tests. All analyzed Dn genes are clustered and linked to markers Xgwm111 and Xgwm44 on the short arm of wheat chromosome 7D. The linked markers and genetic relationships of these Dn genes will greatly facilitate their use in wheat breeding and deployment of aphid-resistant cultivars.
Soybean Pubescence Color Gene
The T locus of soybean controls pubescence and seed coat color, and it encodes a flavonoid 3'-hydroxylase (F3'H). Alleles at the locus are associated with chilling tolerance. Toda et al. (2212–2217) cloned the entire F3'H gene and exhibited that it consists of three exons and two introns distributed in a 8500-bp DNA segment. The promoter contains a G-box, two MYB-binding domains, and TA-repeats. The structure and number of the TA repeats was cultivar dependent and polymorphic. A pair of SSR primers was developed to flank the repeats. The SSR marker is applicable even among cultivars with similar pubescence color. This work may be useful for investigations on the transcriptional control and transgenic experiments to clarify the relationship between F3'H gene and chilling tolerance.
Antioxidant Metabolism in Cotton Seedlings
Exposure of cotton seedlings to unfavorable temperatures is thought to result in diminished performance. In this experiment, Mahan and Mauget (2337–2345) monitored the role antioxidant metabolism plays in protection of plants against damage. Antioxidant metabolism was monitored in cotton seedlings that experienced both high and low temperatures in the field. Antioxidants varied in the plants, but the variation was not associated with either high or low temperatures. It is suggested that seedling antioxidant metabolism may be sufficient to prevent oxidative damage.
Cemetery Collections of Smooth Bromegrass
Smooth bromegrass is poorly adapted to management-intensive rotational grazing because of slow and limited regrowth potential. To find existing germplasm with tolerance to frequent cutting, Casler and Brummer (2510–2516) evaluated smooth bromegrass germplasm from fence and sod habitats of 30 rural cemeteries in Iowa, Minnesota, and Wisconsin. Populations were tested under three harvest frequencies. Although most cemetery populations had lower forage yield than cultivars, there were a few cemetery sod populations with high forage yield potential, more stable forage yield across harvest managements, and greater regrowth percentage under the more frequent harvest management. Smooth bromegrass germplasm from some cemetery sods appears to have potential value for developing cultivars with tolerance to frequent defoliation.
Isolation of Maize by Time and Distance
Management of pollen-mediated gene flow (PMGF) is crucial to the development of new genetic products in maize. Halsey et al. (2172–2185) studied the effect of time and distance isolation together on PMGF in California and Washington, using kernel color to measure outcrossing from source plots 0.4 to 1.2 ha in size. Genetic isolation at the level of <0.01% outcrossing was achieved at 500 m when source and receptor plot flowered together, and at 62 m or less when 2 wk of temporal separation was employed. No outcrossing was seen at 750 m and 2 wk of temporal separation.
Iron-Deficiency Chlorosis Resistance in Soybean
Breeding for soybean resistant to iron-deficiency chlorosis (IDC) is slowed by the impact of environment on resistance expression. Molecular marker-assisted selection (MAS) has been proposed to expedite breeding for IDC resistance. After examining molecular markers located in previously identified quantitative trait loci for IDC resistance, Charlson et al. (2394–2399) identified Satt481 in a breeding population to be consistently associated with IDC resistance. If lines were to be derived from the same population, this marker could be used in the future, to test efficacy of MAS for IDC resistance in soybean.
Genetic Diversity among CIMMYT Maize Inbred Lines
CIMMYT maize inbred lines, useful for the formation of hybrids and synthetic populations bred for subtropical, tropical midaltitude, and highland megaenvironments, were assayed by Xia et al. (2573–2582) using 79 microsatellite markers. High levels of diversity were encountered, with a total of 566 alleles, an average of 7.2 alleles per locus, and average polymorphic information content values of 0.64 per locus scored in this study. The modified Roger's distance (MRD) between pairs of inbreds averaged 0.78, with a range of 0.45 to 0.93. Discrete clusters were difficult to identify within and often between megaenvironments. Exceptions included highland adapted flint and dent lines and subtropical lines derived from Populations 501 and 502. Specific recommendations for nontemperate hybrid maize breeding were made.
Leaf Area Estimate of White Clover
The relationship between length of midrib of the central leaflet and whole area of trifoliate leaves in white clover (Trifolium repens L. cv. Milkanova) was analyzed by Gamper (2552–2556) to nondestructively estimate the leaf area of clonal propagates of nine plant genets. A simple predictive log-linear relationship is introduced to estimate the area of trifoliate leaves from the lengths of the corresponding middle leaflets. Genet-specific coefficients are reported for the predictive linear correlation between the logarithms of leaf area and length. Differences among plant genets suggest that separate coefficients should be determined for the analyses of leaf-area formation in experiments, which involve clonal propagates of different genets.
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