| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
A natural high oleic acid castor (Ricinus comunis L.) mutant line with 20-fold increase in oleic acid (
780 g kg–1) and a 6-fold decrease in ricinoleic acid content (140 g kg–1) compared with standard castor oil (40 g kg–1 and 870 g kg–1, respectively) has been obtained. In this research, Rojas-Barros et al. (157–162) investigated the inheritance of this trait. Results revealed that the high oleic content is determined by an interaction between a recessive allele, ol, at one locus and a dominant allele, Ml, at a second locus. The information provided by this genetic study will facilitate the transfer of the high oleic trait to castor cultivars.
Durum Wheat Quality Studies
Detailed agronomic and quality studies of durum wheats carrying glutenin subunits 1Dx5 and 1Dy10 on a translocated chromosome segment have not been completed. Klindworth et al. (77–84) conducted yield trials and quality tests of 14 translocation lines to determine if the translocated segment would have a detrimental effect on agronomic traits and determine if baking quality of the lines was improved. Yields of translocation lines were only slightly lower than that of check cultivars, but dough mixing characteristics were inconsistent and loaf volumes were not significantly improved. The results suggest that inserting subunits 1Dx5 and 1Dy10 into durum will, by itself, not result in durum with acceptable baking quality.
Organelle Genome Inheritance in Buffalograss
Diversity and mode of organelle genome inheritance are unknown in buffalograsses [Buchloë dactyloides (Nutt.) Engelm.]. Gulsen et al. (186–192), using universal chloroplast and mitochondrial primer pairs, amplified by polymerase chain reaction six cpDNA and three mtDNA noncoding regions from 56 genotypes collected from diverse locations in the North American Great Plains. Each amplified fragment was then digested with two to six different restriction enzymes. Out of the 56 genotypes studied, nine (16%) were discriminated from the other buffalograsses. The cpDNA was determined to be maternally inherited in buffalograss. These results suggest that low levels of organelle DNA PCR-RFLP are present in naturally occurring buffalograss populations and cytoplasmic incompatibility within ploidy level crosses is unlikely.
Salinity Assessment of Halophytic Grasses
Assessment and classification of salt tolerance within ecotypes of a halophytic grass species requires realistic criteria. Direct selection criteria based on growth data must be used before potential indirect selection criteria can be determined. However, the growth response curves to increasing salinity of halophytic plants differ from glycophytes, which traditional classification criteria are based on. Lee et al. (251–258) used growth responses of seashore paspalum (Paspalum vaginatum Sw.) ecotypes to illustrate issues that arise in development of salinity assessment and classification criteria for halophytic grasses. Minimum screening criteria are suggested based on the reliability of various criteria to distinguish salinity tolerance among ecotypes.
Determining Available Nitrogen by Anion Exchange Membranes
The potential of anion exchange membranes (AEMs) for determining available nitrogen in soils of turfgrass systems has not been extensively researched. Mangiafico and Guillard (259–265) found significant linear response plateau models between turfgrass reflectance meter measurements and NO3–N desorbed from AEMs. These models suggest that critical levels of soil NO3–N could be determined to maximize turfgrass color measurements without excessive N application. This study also found significant relationships among measurements from two hand-held reflectance meters and chlorophyll concentration in turf leaves. These findings suggest both AEMs and hand-held reflectance meters could be useful tools for N management in turfgrass.
Medicago sativa subsp. falcata and subsp. sativa Testcrosses
Riday and Brummer (8–17) evaluated a broad range of Medicago sativa subsp. falcata germplasm to identify those that produce the best hybrids in testcrosses with elite subsp. sativa genotypes. The highest yielding sativa–falcata hybrids were derived from European falcata germplasm. Preselection of parental falcata genotypes for autumn growth resulted in higher yielding testcross progeny. Narrow sense heritabilities for yield measurements were very low (0.12–0.33). Expected genetic gain per selection cycle was greater using progeny testing than simple recurrent phenotypic selection.
Overexpression of Polyphenol Oxidase
Color intensity of raw sugar is an important quality parameter affecting its market value. Color in raw sugar is partly a result of reactions affected by the enzyme polyphenol oxidase (PPO). Vickers et al. (354–362) attempted to reduce PPO activity, and hence color intensity, by constitutive expression of a full-length polyphenol oxidase cDNA in sense or antisense orientation. PPO activity was measured in transformed plants grown in the field and correlated significantly with the color of juice and raw sugar. PPO activity was nonspecifically elevated and juice color darker in all types of transgenic plants. Sense transformed plants, however, had higher levels of PPO mRNA and higher activity in the stem than other clones. This is the first targeted manipulation of an endogenous gene in sugarcane leading to altered enzyme activity. Sugar crystals made from the juice of plants differing in PPO activity showed corresponding differences in color. This observation and the positive correlation between juice color and PPO activity support the hypothesis that lowering PPO activity could reduce the color intensity of juice and raw sugar.
Phenotypic Variation in Switchgrass Populations
Switchgrass (Panicum virgatum L.) is a widely adapted warm-season perennial that has considerable potential as a biofuel crop. Casler (388–398) characterized phenotypic variation of 49 switchgrass populations from a wide geographic section of the USA. Little of the phenotypic variability among populations could be attributed to systematic climatic, edaphic, or geographic factors. There was a trend toward phenotypic differentiation between ecoregions and hardiness zones of the eastern USA, suggesting that these classifications can be useful in characterizing switchgrass germplasm. Most switchgrass populations can be utilized for conservation and restoration projects throughout a combined ecoregion and hardiness zone without undue concern over contaminating, diluting, or swamping the local switchgrass gene pool.
Markers for NDF
Intake potential is the most important quality component of a forage crop, accounting for up to 70% of the variation in animal performance. Neutral detergent fiber (NDF) concentration is the most important laboratory predictor of intake potential in forage crops. Diaby and Casler (27–35) set out to identify molecular markers that could be used to increase the efficiency of breeding smooth bromegrass (Bromus inermis Leyss.) for decreased NDF concentration. The found several DNA markers that showed strong correlations with NDF within individual populations and one marker that showed strong correlations with NDF across all populations of plants. They concluded that marker selection or marker-assisted selection may improved the efficiency of breeding for reduced NDF concentration in smooth bromegrass.
NDF Concentration Is Linked to Reductions in Forage Yield
Selection for reduced neutral detergent fiber (NDF) concentration has been used as a mechanism of improving intake potential of perennial grasses by ruminant livestock. However, reduced NDF concentration is typically associated with reduced forage yield. Casler (36–43) determined that these responses are due mainly to genes that affect both traits and partly to two other phenomena: linkage of genes affecting the two traits independently and inbreeding. Natural selection among smooth bromegrass genotypes within sward plots also appears to reduce the magnitude of this correlation over time. Nevertheless, the magnitude and consistency of this genetic correlation suggests that it will be extremely difficult to reduce NDF concentration without concomitant reductions in forage yield.
Breeding Reduced NDF Concentration in Smooth Bromegrass DNA
Voluntary intake is generally considered to be the single most important factor limiting animal performance on high-forage diets. Neutral detergent fiber (NDF) is the laboratory variable most closely associated with voluntary intake potential. Casler et al. (44–50) used several clones of smooth bromegrass (Bromus inermis Leyss.) and their progenies to measure the genetic correlation between forage yield and NDF. They determined that the high and positive genetic correlations observed between these two traits are mostly due to a physiological relationship between the traits, that high NDF confers, in part, high forage yield. However, the relationship was partly broken by crossing and selection, indicating that plant breeders can devise selection schemes to simultaneously improve forage yield and decrease NDF.
Creeping Bentgrass Tolerance to Snow Mold Fungi
Creeping bentgrass (Agrostis stolonifera L.) is one of the most important cool-season grasses for golf courses. Wang et al. (399–406) evaluated a large population of creeping bentgrass clones for their tolerance to snow mold fungi. Clones were selected from putting greens and fairways of old golf courses in Wisconsin. Clones from fairways were more tolerant of snow mold, most likely due to long-term natural selection in the absence of fungicide applications. Snow mold tolerance in creeping bentgrass appears to be non-specific with respect to race and species of snow mold isolates. Selection for increased tolerance to snow mold fungi should be successful, but must be based on evaluations over multiple inoculation runs.
Population Structure and Breeding Patterns in U.S. Rice Cultivars
Information on population structure and breeding patterns of U.S. rice (Oryza sativa L.) varieties is important for genetic improvement of this crop. Lu et al. (66–76), using microsatellite markers, analyzed by genetic distance-based and model-based cluster analysis varieties representing U.S. rice production from 1900 to 2000. Their study showed that population structure in U.S. rice was established before 1930 and has remained fairly intact to the present. This information provides the foundation for novel methods of exploiting the genetic potential in rice for developing improved varieties.
Glyphosate Tolerant Transgenic Corn
5-Enol-pyruvylshikimate-3-phosphate synthase from Agrobacterium sp. CP4 has been used to engineer transgenic events with high glyphosate tolerance that have been released under the Roundup Ready trademark. Heck et al. (329–339) sought to produce a comparable event in corn (Zea mays L.). On the basis of molecular, expression, and efficacy criteria, we selected the NK603 event as an event meeting the numerous criteria for glyphosate tolerance in a field setting. The NK603 event contains a single, simple transgenic integration and has shown trait stability over many generations.
Evaluation of Multienvironment Trials of Peanut Cultivars
The objective of this work was the simultaneous analysis of several multienvironment trial (MET) to identify megaenvironments and superior cultivars for the peanut (Arachis hypogaea L.) crop area in Argentina. Casanoves et al. (18–26) analyzed a 6-yr series of grain yield data from MET, using six by-year analyses of complete yield data sets and an AMMI mixed model analysis combining all six years of MET. The results allowed us to identify superior cultivars and confirm the existence of a unique megaenvironment for identifying high yield peanut cultivars. The AMMI mixed model approach of MET data was successfully implemented to analyze highly unbalanced genotype–environment data sets.
Marker Development in Cultivated Peanut
Peanut (Arachis hypogaea L.) is important in the economy and nutrition in the USA and abroad; it is virtually unexplored at the genomic level because of the genome complication and size (2800 Mb, or about the size of the human genome). Luo et al. (346–353) developed a small database of expressed sequence tags (EST) that will facilitate gene discovery via microarray chips and development of DNA markers. Two cDNA libraries were constructed by mRNA prepared from peanut leaves and immature pods. Randomly selected cDNA clones were partially sequenced to generate ESTs; about 400 unigenes have been selected and arrayed on glass slides for gene expression analysis. The EST analysis described here indicates that our approach is useful for identifying peanut genes on the basis of homologous sequence comparison and for developing EST-derived markers for breeding.
Selecting a Product-Yield Index and Response Function for Crop Tolerance
Product yields resulting from agricultural crops grown subject to increasing levels of root-zone salinity decrease according to a sigmoidal-shaped response. Steppuhn et al. (209–220, paper I) made comparisons among six possible empirical response models applied to the results from a spring wheat and 16 other test crops and found that the modified compound–discount function was the most precise. This function features two parameters: the salinity level causing a 50% product loss and the absolute value of the general decline in relative crop yield with salinity at and about the 50% yield level. Combined, these parameters form a salinity tolerance index (the ST-Index) useful in developing crop lists of tolerances to root-zone salinity.
Indices for Tolerance in Agricultural Crops
Since 1977, crop tolerance lists have been based on the two-piece threshold-slope linear response model that approximates the more precise modified discount function. Evaluations of direct, analytical, and empirical methods for converting the threshold-slope parameters to those of the discount function resulted in selected conversion procedures with errors of ±10% or less for eight test crops (rye, sorghum, wheat, Harding grass, ryegrass, alfalfa, carrot, and turnip). Steppuhn et al. (221–232, paper II) used these selected procedures to provide a list of the inherent tolerances for root-zone salinity associated with agricultural crops based on the nonlinear Salinity Tolerance Index.
Expression of Fatty Acid Mutations in Ethiopian Mustard
Ethiopian mustard (Brassica carinata A. Braun) mutants with very high concentration of oleic acid (839 g kg–1) or with very low concentration of linolenic acid in seed triacylglycerols (15 g kg–1) have been developed. Nabloussi et al. (202–208) investigated the expression of the altered fatty acid profiles of these mutants in different plant tissues and stages of seed development and germination. Both the high oleic and the low linolenic acid traits were expressed in pollen, roots, and leaves, as well as during the whole seed developing period and in cotyledons after seed germination. Comparison of these results with previous studies on Brassica napus and Arabidopsis mutants suggested that the high oleic acid mutant might show altered activity at both FAD2 and FAD3 microsomal desaturases, whereas the low linolenic acid mutant might show reduced activity at FAD3 level.
Isoyield Environments for Field Pea Production
Cultivars are often recommended to producers based on their averaged yields across sites within a geographic region. However, this geography-based approach assumes that all sites in a given region have the same level of production capacity. Yang et al. (106–113) described a performance-based approach to identifying sites of isoyield groups with similar yielding ability and its use for analyzing the yield data from field pea (Pisum sativum L.) cultivar trials conducted in Alberta, Canada, from 1997 to 2001. The isoyield analysis was able to cluster 34 test sites across years into seven isoyield groups. The identification of isoyield environments allowed for choosing appropriate cultivars for specific environments and improving the efficiency and quality of cultivar testing programs.
Physiological Processes and Wheat Yield Progress in the UK
The growth and development of eight UK wheat (Triticum aestivum L.) cultivars introduced from 1972 to 1995 were examined by Shearman et al. (175–185). A linear genetic gain in grain yield of 0.12 Mg ha–1 yr–1 (1.2% yr–1) was positively correlated with both harvest index and aboveground biomass. There was a linear increase across time of 217 grains m–2 yr–1. Our results suggest that recent genetic gains in grain yield have been based on a combination of improved growth rate in the preanthesis period, which has driven increases in the number of grains per square meter, and a larger source for grain filling through increases in stem soluble carbohydrate reserves.
QTL Mapping of Resistance to Thrips in Common Bean
The melon thrips (Thrips palmi Karny) is a serious pest of common bean (Phaseolus vulgaris L.) in various parts of the Americas since its introduction from Asia. Estimated yield losses from melon thrips in snap bean average 30%, and can reach 100% in susceptible dry bean genotypes. Host plant resistance offers an opportunity to control melon thrips without the use of insecticides. A study was conducted by Frei et al. (379–387) to identify quantitative trait loci (QTLs) for resistance to melon thrips in common bean using recombinant inbred lines and genetic mapping. A major QTL was found on linkage group b06 which was named Tpr6.1.
Species Diversity and Composition of Pastures
Knowledge of factors that influence species diversity and composition of pastures is important to forage managers. Guretzky et al. (282–289) examined the effects of landscape position and stocking system on species diversity and functional composition of southeastern Iowa pastures. Overall species diversity was greatest on backslope landscape positions within pastures managed with either continuous or rotational stocking. Rotational stocking, however, had more desirable effects by producing greater legume cover and less weed cover than pastures managed with continuous stocking. Our research suggested that spatial components of pastures must be considered to optimize forage productivity and quality for grazing livestock.
Winter Wheat Selection for the Southern Great Plains
Winter wheat (Triticum aestivum L.) cultivars used in the southern Great Plains are traditionally developed in a grain-only (GO) production system even though many producers in this region will graze and harvest grain form the same wheat crop. Productivity of wheat used in a dual-purpose (DP) production system may be compromised with wheat cultivars derived using a GO production system. MacKown and Carver (322–328) evaluated forage traits at the onset of fall grazing for subpopulations of 24 unique pedigrees that were bulk selected from GO and DP production systems. Nearly always, the effect of selection environment was consistent across genetic backgrounds. Among the pedigrees, there were significant two- to three-fold differences in nitrate-N. Selection in the DP system appears to offer equal or slightly less fall forage biomass without greatly changing forage total-N or affecting nitrate-N concentrations.
Influence of P and K on Alfalfa Yield
Yield and persistence of alfalfa (Medicago sativa L.) are positively associated with adequate K and P nutrition, but how these nutrients impact yield are not understood. Berg et al. (297–304) determine how alfalfa yield components change with fertility-enhanced yield increases. Increases in mass per shoot were consistently associated with increased forage yield, while plant populations and shoots per area were unaffected or declined slightly with fertilizer applications that led to high forage yield. Because fertilizer responsiveness is closely associated with greater mass shoot–1, cultivars possessing this trait may be relatively more productive under well-fertilized conditions.
Furrow-Irrigated Alfalfa and Tall Wheatgrass Pastures
Beef stockers rotationally and continuously grazed alfalfa (Medicago sativa L.) and tall wheatgrass [Agropyron elongatum (Host) Beauv., = Elytrigia elongata (Host) Nevski] monocultures and mixtures (Lauriault et al., 305–315). Because of differences in stocking rate and average daily gain, pastures containing alfalfa produced twice the gain ha–1 of monoculture tall wheatgrass. Bloat was not observed in cattle grazing continuously stocked alfalfa–tall wheatgrass pastures, but it was in rotationally stocked alfalfa pastures every year. Lack of bloat under continuous stocking was attributed to a more stable plane of nutrition. Producers may improve animal gain ha–1 by including alfalfa in tall wheatgrass pastures and possibly reduce the incidence of bloat by continuous stocking.
Global Climate Change and Nutritive Value of Rhizoma Peanut
There are few long-term studies evaluating the effect of increasing atmospheric temperature and CO2 concentration on nutritive value of perennial forage legumes. In this study, Newman et al. (316–321) quantified the effects of these factors on rhizoma peanut (Arachis glabrata Benth.) nutritive value and fiber components. Elevated CO2 had no effect on nutritive value, but increasing temperature decreased herbage digestibility. This decrease was associated with a greater proportion of lignin in both acid- and neutral-detergent fiber. Changes in global climate that result in increased temperature will likely have a negative effect on nutritive value of forages consumed by livestock.
Soybean and Cotton Cropping Sequences and Reniform Nematode in Texas
Eighteen soybean [Glycine max (L.) Merr.] cultivars of maturity group 5, 6, 7, and 8 were tested in Rotylenchulus reniformis-infested soil either nonfumigated or fumigated with 1,3-dichloropropene. Westphal and Scott (233–239) compared reproductive rates of R. reniformis in the first year, and both experiments were planted with cotton (Gossypium hirsutum L.) in the second year to measure the rotational effects of soybean on cotton yield compared with grain sorghum [Sorghum bicolor (L.) Moench] and fallow. High-yielding soybean cultivars with potential to suppress reniform nematode (HY574, Padre, DP7375RR, and NK83-30) were identified. These soybean cultivars may provide an alternative to grain sorghum in cotton cropping sequences in South Texas.
Glutathione and Ascorbate Metabolism in Cotton under Water Stress
Water stress results in the production of oxidants that can damage plants. These oxidants are metabolized into nonreactive forms to prevent cellular damage. In this study, Mahan and Wanjura (193–201) monitored the seasonal pattern of antioxidant metabolism in cotton (Gossypium hirsutum L.) under water stress in the field. In the 2-yr study it was found that glutathione metabolism did not vary in response to water stress, while ascorbate metabolism was responsive. Malondialdehyde, an indicator of oxidative damage, did not increase under water stress, suggesting that antioxidant metabolism was sufficient to prevent oxidative damage.
Yield Improvement in Watermelon
High yield is a major goal for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] breeders. Gusmini and Wehner (141–146) measured yield in a diverse set of watermelon cultivars in North Carolina in 2001 and 2002 to identify high-yielding germplasm for use in breeding programs. The authors also compared yield of obsolete vs. modern germplasm and F1 hybrids vs. inbred cultivars. Yield was evaluated in replicated experiments in three environments. Consistent and significant yield differences among the 80 cultivars across environments suggests genetic variation for the trait. In addition, high-yielding cultivars for use in breeding programs were identified.
Related articles in Crop Science:
| ||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Plant Registrations | Soil Science Society of America Journal | ||||
| Journal of Natural Resources and Life Sciences Education |
Journal of Environmental Quality |
||||
