| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
To examine the mechanism of resistance to soybean cyst nematode in resistant soybean germplasm PI 437654, Nelsen et al. (265–273) hybridized BAC clones associated with the Rhg4 locus to genomic DNA from germplasms displaying different responses to soybean cyst nematode. A specific genomic polymorphism involving a novel soybean subtilisin-like protease, GmSUB1, was identified. Sequences for promoter and full coding region were obtained (GenBank AY277949). GmSUB1 shows increased gene copy number and increased levels of expression in PI 437654. GmSUB1 is believed to be secreted into the extracellular matrix, and may be involved in cell wall reorganization and activation of signal transduction pathways.
High Oleic Acid Castor
Castor (Ricinus communis L.) is an oil crop whose seed oil is very rich in ricinolic acid and poor in oleic acid. Rojas-Barros et al. (76–80) report the isolation of a natural high oleic castor mutant with 780 g kg–1 of oleic acid vs. 40 g kg–1 of the standard castor oil and decreased levels of ricinoleic acid, 140 vs. 870 g kg–1. The isolation of high oleic/low ricinoleic mutations signifies an important advance in the development of ricinoleic acid free/very high oleic acid castor oil lines with potential industrial and food applications requiring very high oxidative stability. The trait can be very useful for genetic and biosynthetic studies.
Nutritional Quality of Wild Jerusalem Artichoke
Knowledge of the nutritional quality of wild Jerusalem artichoke (Helianthus tuberosus L) forage is essential to breed for improved quality. Seiler and Campbell (289–292) determined the genotypic variability for N, P, K, Ca, and Mg in the forage of nine populations of wild Jerusalem artichoke. N, Ca, Mg, and K levels were adequate, but P was low. Genotypic variance components for N, Ca, and K were sufficiently high for improving forage quality, but P and Mg were low indicating that it would not be possible to increase the concentration of these elements.
Single-Achene Sunflower Selection Procedure
The recent development of a sunflower (Helianthus annuus L.) mutant with a high stearic acid concentration nonuniformly expressed along the seed suggests the need for a single-achene selection procedure alternative to traditional half-seed analysis. Velasco et al. (93–97) evaluated the potential of near-infrared reflectance spectroscopy (NIRS) for analyzing the fatty acid composition of single husked achenes of sunflower. Calibration equations for stearic acid, oleic acid, and linoleic acid were developed from a wide spectrum of breeding materials. The evaluation of the performance of the calibration equations within a selection program revealed a close relationship between the results provided by NIRS and gas-liquid chromatography, with r2 of 0.83 for stearic acid, 0.92 for oleic acid, and 0.93 for linoleic acid concentration. It was concluded that NIRS can be used for nondestructive selection for these major fatty acids at a single-achene level.
White-Flowered Wild Soybean Accession
All wild soybean [Glycine soja (Sieb. and Zucc.)] accessions in the USDA Soybean Germplasm Collection have purple flowers. There are a few white-flowered G. soja accessions in the Chinese germplasm collection, but most of these accessions have a 100-seed weights of more than 3.0 g, indicating that these accessions may be descended from recent hybridizations with soybean [Glycine max (L.) Merr.]. There is no explanation for why white flowers could not occur in G. soja, but there has been skepticism that such a type does exist. Chen and Nelson discovered a white-flowered plant within wild soybean accession PI 424008A and demonstrated (339–342) that it originated from a natural mutation.
Glycine Genetic Diversity
Some annual Glycine accessions are intermediate between the standard phenotypes of G. max (L.) Merr. and G. soja Sieb. & Zucc. and have been labeled semiwild. Both phenotypic measurements and RAPD markers were able to distinguish among these three groups and among the accessions analyzed; unique RAPD markers were found for each taxonomic type. Chen and Nelson (316–325) found that on the basis of the analysis of RAPD data, G. soja accessions have the greatest genetic diversity and semiwild accessions the least. Glycine max and semiwild accessions are more closely related to each other than to the G. soja accessions.
Genetic Relationship among Smooth Bromegrass Cultivars
The genetic relationship among smooth bromegrass (Bromus inermis Leyss.) cultivars belonging to the northern, southern, and intermediate were analyzed by means of 176 AFLP markers by Ferdinandez and Coulman (241–247). Cluster analysis and principle component analysis grouped the cultivars according to their pedigrees rather than by ecotypes. The older southern cultivars grouped distantly from recently developed cultivars of the same ecotype. The northern type cultivars grouped with the recently developed southern and intermediate cultivars. Higher molecular variations observed in the recently developed southern and some northern cultivars reflect the diverse genetic backgrounds of the source populations. AFLP markers differentiated phenotypically similar smooth bromegrass cultivars according to their breeding history.
Increased Sunflower Stearic Acid
Sunflower (Helianthus annuus L.) genotypes with increased stearic acid (C18:0) content in their seed oil are useful for food and industrial applications. Pérez-Vich et al. (70–75) report the development and characterization of two midstearic sunflower lines by isolating genotypes homozygous recessive for single genes from the high stearic acid mutant CAS-3 (stearic acid content 250 g kg–1, genotype es1es1es2es2). The lines were named CAS-19 (168 g kg–1; es1es1Es2Es2) and CAS-20 (83 g kg–1; Es1Es1es2es2). The new genotypes expressing midstearic acid levels represent a further advance toward the development of sunflower lines for specific edible purposes, and constitute a unique source for agronomic and genetic studies.
U.S. Hard White Winter Wheat Production
The production of hard white winter (HWW) wheats (Triticum aestivum L.) in the USA is expected to increase in the future and to replace partially the traditional hard red winter (HRW) wheats. To monitor the effects of this change, Pike and MacRitchie (173–176) evaluated HWW wheat lines for protein composition and functional quality and compared them with HRW wheat lines. The percentages of the different classes of proteins, measured by size exclusion-HPLC, were similar in HWW lines to those of the HRW lines. Quality characteristics of the white wheat lines as measured by lactic acid solvent retention capacity, mixograph dough development times, and bake-test bread volume also equaled those for the red wheats. These data should serve as a benchmark for HWW wheats as more cultivars are released.
Improving Nutritive Value of Timothy
Improving nutritive value is an important breeding objective in timothy (Phleum pratense L.). Forage digestibility can be improved either by selecting for reduced fiber concentration or by increasing the digestibility of the cell wall, which is composed primarily of lignin, cellulose, and hemicellulose. Claessens et al. (81–88) applied divergent phenotypic selection to 78 high yielding timothy genotypes for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose (HEM), and cellulose (CEL) and for ratios of ADL/HEM, ADL/CEL, ADL/(HEM+CEL). Selection based on NDF, ADF, HEM, and CEL concentrations did not consistently result in higher in vitro true digestibility and dry matter (DM) yield. However, ADL/(HEM+CEL) and ADL/CEL ratios seemed to be promising selection criteria to increase digestibility while maintaining or increasing DM yield.
Accurate Assessment of Forage Nitrate
Timely and accurate assessment of nitrate in forage can be used to limit risks of excessive nitrate intake by livestock. To determine the suitability of nitrate field-tests, MacKown and Weik (218–226) evaluated laboratory and quick-test nitrate assays and compared nitrate extractions of fresh field samples to oven-dried and ground forage samples. Among the quick-test nitrate assays, a small hand-held test strip reflectance meter was easiest to use and nearly as accurate as measurements following enzymatic nitrate reduction. Nitrate extraction was less efficient from fresh forage than from oven-dried forage and must be improved or properly calibrated with dry tissue before making accurate field estimation of forage nitrate levels.
Spring Wheat Resistance to Imidazolinone Herbicides
The imidazolinone herbicides are an attractive alternative for weed control in spring wheat (Triticum aestivum L.). However, spring wheat is sensitive to most imidazolinone herbicides. Using seed mutagenesis, Pozniak and Hucl (23–30) were success in isolating six mutants with moderate to high levels of resistance to imazamox. Resistance in all lines was simply inherited. Allelism studies indicated the presence of three independently segregating resistance genes. Resistance was additive with higher levels of resistance noted in lines with more than one resistance gene.
Genetic Diversity of Barley Landrace in Oman
Subsistence farmers in the Batinah region of Oman grow a local landrace of barley (Hordeum vulgare L.) in a mixture with alfalfa (Medicago sativa L.) for fodder in a unique irrigated farming system. Jaradat et al. (304–315) characterized seven subpopulations of the landrace for 26 seed and spike quantitative and qualitative traits, quantified phenotypic diversity, and explored significant variation for selection and breeding. Most diversity was partitioned within subpopulations, and the hierarchical, nonrandom trait associations indicate adaptive responses to environmental and human selection. The long history of in situ conservation of this landrace in a multitude of irrigated farming systems contributed to its high diversity.
New Transgenic Cottons
Cotton (Gossypium hirsutum L.) cultivars engineered to resist glyphosate [N-(phosphonomethyl)glycine] herbicide are reproductively resistant to topical glyphosate applications before the four-leaf stage. Growers may apply two glyphosate treatments as long as two nodes of growth and 10 d elapse between sprays before the four-leaf stage. May et al. (234–240) tested new transgenic cottons putatively reproductively resistant to glyphosate later in crop development by topically spraying glyphosate four times between the four- and 14-leaf stages. They demonstrated through yield, fruit weight, and fruit distribution that the new transgenic cotton yields and fruits the same with or without glyphosate treatment and better than the transgenic control cotton representing current commercial glyphosate resistant cotton cultivars.
Increased Soybean Oil Content
Increasing oil in seeds of soybean [Glycine max (L.) Merr.] may add value to the crop. Feng et al. (63–69) used two recurrent half-sib selection systems devised for soybean to select for increased oil content, one using a high-oil tester and one using a low-oil tester. Cycles of half-sib selection using the high-oil tester successfully increased oil content, while using the low-oil tester did not. Evidence of heterosis indicated that dominance effects on oil content were present. A high-oil tester and high-oil breeding populations may have common alleles resulting in less dominance and more additive effects in their hybrids. Consequently, a high-oil tester can potentially provide better evaluation and selection precision.
Phytochrome-B-Overexpressing Potatoes
Arabidopsis thaliana (L.) Heynh. phytochrome-B-overexpressing transgenic potatoes (Solanum tuberosum L.) have been reported to exhibit greater leaf physiological potential and increased yield. To elucidate the physiological basis for this yield superiority, Schittenhelm et al. (131–143) compared transgenic (Dara-5) and wild-type plants under different light levels in a greenhouse and a growth chamber experiment. The transgenic plants showed consistently greater leaf C exchange rate, leaf conductance, chlorophyll concentration, and Rubisco activity than the wild-type plants. However, only at low light levels in the growth chamber did the transgenic plants produce slightly greater tuber and total biomass yield. Transgenic overexpression of phytochrome B does not appear to be a promising strategy to improving potato yield.
AFLP Variation in Four Blue Grama Seed Sources
Development of adaptive germplasm of native plants for reclamation and groundcover is challenging, not only in improvement of seed production but also in maintenance of the genetic diversity sampled from natural populations. Fu et al. (283–288) showed that a balanced composite of multisite blue grama [Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths] germplasm representing 11 natural populations in Manitoba, Canada, not only had more variation revealed by amplified fragment length polymorphism than the ecotype Bad River, a Minnesota ecotype, and a Manitoba seed harvest, but also maintained the diversity with little genetic shift in the first two generations of seed multiplication.
Spatial Analyses Across Locations And Years
Spatial analyses of yield trials are a powerful method of adjusting treatment means for spatial variation and improving statistical precision of mean estimation. Because yield trials are typically repeated across multiple locations and years, spatial analysis methods must be adapted for combined analyses across locations and years. Smith and Casler (56–62) described three methods of conducting spatial analysis of forage yield trials across locations and years. They found that the most flexible method, which resulted in potentially different adjustments for each harvest, location, and year, gave the greatest improvements in trial precision. They also showed that full-season single-harvest trials may be less sensitive to the effects of spatial variation than multiple-harvest trials. Their results provide a mechanism for researchers to conduct spatial analyses across multiple locations and years of a single yield trial.
Latitudinal Adaptation of Switchgrass Populations
Switchgrass (Panicum virgatum L.) is a potentially important and widely adapted crop for use in biofuel production. Casler et al. (293–303) demonstrated that much of the inconsistency in biomass yield of switchgrasses across diverse locations can be explained by information on population origin and site characteristics. Upland and lowland types of switchgrass are distinctly adapted to northern and southern latitudes, respectively. Furthermore, there are northern- and southern-adapted populations within both upland and lowland types. Differential adaptation probably derives from photoperiodism, genetic variation for cold and heat tolerance, and the accumulated effects of evolutionary processes including mutation, migration, and natural selection. There appears to be sufficient genetic variability within switchgrass to extend the adaptation zones of both upland and lowland types.
Untimely Fall Harvest and Alfalfa Yield
Dhont et al. (144–157) assessed the impact of the timing of a fall harvest (two harvests only, or a third harvest at 400, 500, or 600 growing degree days [GDD] after the second one) on persistence, dry matter yield (DMY), and root organic reserves of field-grown alfalfa (Medicago sativa L.). The DMY of the first harvest was significantly reduced by fall harvests taken at 400 or 500 GDD, but seasonal DMY remained advantageous with the regrowth intervals of 500 or 600 GDD. Root dry weight and amounts of root carbohydrate and N reserves were significantly reduced by harvesting at 400 or 500 GDD.
Survival of Legumes in Pastures
How landscape position affects emergence and survival of legumes seeded into pastures is not well known. Guretzky et al. (227–233) conducted an experiment that examined the influence of landscape position, N fertilizer, and sward height on emergence and survival of legumes seeded into pastures. On summit landscape positions, poor survival of seedlings limited establishment of legumes. The reduction of grass competition enabled successful establishment of legumes on backslopes. In pastures varying in landscape position, legumes should be seeded on backslopes, N fertilizer should not be applied, and grass competition should be reduced before seeding legumes.
Soybean Aphid Resistance
In 2000, the soybean aphid (Aphis glycines Matsumura) migrated into North America from Asia, posing a new threat to soybean [Glycine max (L.) Merr.] production. Resistance to the soybean aphid in North American soybean germplasm was unknown, and a project by Hill et al. (98–106) to identify resistance in soybean germplasm began in 2001. More than 1600 soybean cultivars and germplasm accessions were screened for resistance to the soybean aphid with an efficient greenhouse screening method. Resistance was found in nine germplasm accessions. There was strong antibiosis in two resistant sources characterized, while in another, antixenosis was important. These resistance sources will be used to develop soybean cultivars resistant to the soybean aphid.
Niger Seed Yield in the U.S. Northern Great Plains
Niger [Guizotia abyssinica (L. f.) Cass.] is imported into the USA for use as birdseed. Seeding rates, ranging from 0.56 to 16.8 kg ha–1, of the cultivar EarlyBird were evaluated in seven northern Great Plains environments by Kandel et al. (190–197). Maximum yields across all environments corresponded to a seeding rate of 284 seeds m–2 and a plant stand of 157 plants m–2. For production purposes, a seeding rate of 6.7 kg ha–1 provided high yields with early canopy closure and uniform seed maturation.
Hybrid and Pureline Hard Winter Wheat Yield and Stability
Pureline wheat cultivars dominate production fields despite large investments and numerous attempts to introduce hybrids during the past 28 yr. Koemel et al. (107–113) analyzed yield trends and yield stability in both hybrid and pureline entries that were evaluated during a 21-yr period at four locations in Oklahoma, USA. The yield of hybrids increased at a greater rate than that of purelines. No differences in stability between hybrids and purelines were found. Hybrid wheat will not be commercially viable in the southern Great Plains of the USA until the yield advantage is further increased and seed costs reduced.
C-Banding Analyses of Smooth Bromegrass
Smooth bromegrass (Bromus inermis Leyss.) has both tetraploid and octaploid forms. It has been difficult to characterize its chromosomes because of their similarity. Tuna et al. (31–37) used the Geimsa C-banding chromosome staining method and chromosome morphology cytogenetically to characterize tetraploid and octaploid smooth bromegrass. Ideograms or graphic representations of the sets of chromosomes (karyotypes) of each ploidy level of were developed. Comparisons of the karyotypes indicate that the octaploid form is not simply a doubled form of the tetraploid. At least one of its genomes or parent sets of chromosomes is differentiated from the genomes of the tetraploid form. This information will enable bromegrass breeders to efficiently structure their breeding programs.
Related articles in Crop Science:
| ||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
