| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Smooth bromegrass (Bromus inermis Leyss.) is poorly adapted to management-intensive rotational grazing because of slow and limited regrowth potential. In an effort to find existing germplasm with tolerance to frequent cutting, Casler (978–987) collected and evaluated smooth bromegrass germplasm from fence and sod habitats of 30 rural cemeteries in Iowa, Minnesota, and Wisconsin. For most cemeteries, fence and sod populations probably originated from one source of germplasm. Natural selection over many decades, mostly in the sod habitat, has caused fence and sod populations to diverge. Sod populations appear to have developed a lower growing habit and slower growth rate, limiting their forage productivity under both infrequent and frequent harvesting managements. Smooth bromegrass plants from rural cemetery sods may have some value for cultivar development, but do not represent a silver bullet for developing a grazing type of smooth bromegrass.
Rind Penetrometer and ECB Resistance in Corn
Corn (Zea mays L.) yield is affected by a number of factors, including stalk lodging and pests such as the European corn borer (Ostrinia nubilalis Hübner; ECB). Martin et al. (711–717) studied (i) whether rind penetrometer resistance selection for stalk strength affected second-generation ECB feeding, and (ii) how rind penetrometer resistance selection changed relative amounts of strengthening compounds in the stalk and their correlation with ECB feeding. With an increase in rind penetrometer resistance, there was a decrease in second-generation ECB tunnel number and lengths. Also, there were increases and decreases in the stalk components as determined by the high or low direction of selection, respectively, with the exception of silica. This indicated that these components play a role in strengthening of the stalk, and may contribute to less feeding by second-generation ECB.
Ethylene Production of Two Wheat Cultivars under Stress
There have been no studies regarding genetic differences in ethylene production rate (EPR) in wheat (Triticum aestivum L.). In this study, Balota et al. (812–818) compared EPR of two wheat cultivars previously characterized for field performance under drought and heat conditions using a new system of ethylene measurement. ‘Dropia’ (stress resistant) and ‘Delia’ (stress susceptible) were exposed to optimum and stress conditions, including desiccation, high temperature, and paraquat-induced oxidation, and measured for EPR. Additional physiological parameters related to stress resistance were also measured. Under desiccation, EPR decreased more in Delia than in Dropia. Under optimum and all other stress conditions, Delia produced more ethylene. Enhanced EPR by Delia was consistent with all other physiological measurements, indicating that Delia was more stress sensitive than Dropia. Field observations also confirmed that Delia is more drought and heat sensitive.
Vertical Profile of Leaf Senescence in Maize
Rate of leaf senescence and the vertical profile of leaf senescence were quantified by Valentinuz and Tollenaar (827–834) during the grain-filling period in older and more recent maize (Zea mays L.) hybrids, grown at three plant population densities during 3 yr. Rates of leaf senescence were 0.44 and 1.87% d–1 during the first half and second half of the grain-filling period, respectively, and rates were greater in the older than in the newer hybrids. A top-to-bottom profile of leaf senescence was observed during the second half of the grain-filling period, with leaves in the central section of the canopy being the last leaves to senesce, and this phenomenon was more marked in the newer hybrids.
Germination Curves and Germination Characteristics in Turfgrass
Germination characteristics are important for the establishment of grasses. Larsen and Bibby (891–899) used a curve-fitting procedure to investigate the variation in germination characteristics within and among cultivars of the turfgrass species slender creeping red fescue (Festuca rubra L. var. littoralis Vasey), perennial ryegrass (Lolium perenne L.), and Kentucky bluegrass (Poa pratensis L.). Cultivars differed in final germination percentage in all three species, and mean germination time and time from 25 to 75% germination differed in two species. However, seed lots within cultivars also differed considerably in germination characteristics. Cultivar differences should, therefore, be tested against seed lot differences by representing each cultivar by more than one seed lot.
Soybean Resistance to Southern Root-Knot Nematode
To track a major quantitative trait locus (QTL) for southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] (Mi) resistance in resistant soybean cultivars, Ha et al. (758–763) conducted a molecular pedigree analysis of ancestral, Mi-susceptible, and Mi-resistant genotypes. Twenty-two out of 24 Mi-resistant cultivars inherited a 200-bp band at Satt358 and a 238-bp band at Sat_132 from ‘Palmetto’. These markers flank the major Mi resistance QTL on Linkage Group O, and can be effectively employed in breeding for Mi resistance.
Physical Properties of Amended Sands
Putting green rootzones are constructed with sands to avoid compaction and facilitate drainage. A laboratory study by Bigelow et al. (900–907) determined the physical properties of three sand sizes with and without several inorganic amendments or sphagnum peat moss at two incorporation rates. Physical properties varied considerably depending on sand size. Inorganic amendments increased total water holding capacity but did not increase available water. A bioassay for available water indicated that porous inorganics contained more available water than traditional measurement methods. Although the inorganics significantly altered the sand physical properties, they were not as effective as peat for improving water retention in drought-prone sands.
Reed Canarygrass Seed Production Traits
Seed production of reed canarygrass (Phalaris arundinacea L.) is often difficult. Sahramaa et al. (988–996) evaluated seed production traits of eight reed canarygrass cultivars, 14 breeding lines, and 53 Finnish wild populations under northern growing conditions. Elite germplasm and the southernmost wild groups had the best seed production traits. Variation recorded indicated the potential to breed new cultivars with good seed production traits from local and elite populations.
Increased Tocopherol Content In Canola
Tocopherols (
–, ß–, 
–, 
-tocopherol) are antioxidants found in all vegetable oils. As vitamin E, they are important dietary nutrients and is a new objective in canola (Brassica napus L.) breeding. Marwede et al. (728–731) tested three European winter oilseed rape populations of doubled haploid lines in several environments to analyze heritability of tocopherols and correlations with other traits. Heritability for tocopherol content is considerably lower than heritability of oil, protein, or glucosinolate content. No correlation between - and -tocopherol or between tocopherol and oil, protein, and glucosinolate content, respectively, existed. Individual tocopherols can be increased independently from one another without affecting other major quality traits.
Salt Tolerance in Omani Barley
Further enhancement of barley's (Hordeum vulgare L.) relatively high tolerance to salinity stress could improve the profitability of some of the salt-affected soils around the world. To select forage and dual-purpose barley genotypes, Jaradat et al. (997–1007) screened 2308 accessions in seven subpopulations of the Batini barley landrace from Oman for germination and early seedling growth under salinity stress, and established the forage yield–salinity response functions for 10 families within each subpopulation at the growth stage most appropriate for forage production. The relatively high broad-sense heritability estimates found for seed germination and seedling growth attributes under salinity stress may reflect high heritability for tolerance to salinity and would result in high genetic gains in selection and breeding programs. Targeted multitrait selection was instrumental in identifying genotypes with improved salt tolerance, high biomass production, and high rate of recovery after the first forage cut under medium and high salinity stress levels. These genotypes have either short rachilla hairs or high root-to-shoot ratio under salinity.
Eliminating Summer Fallow in the Central Great Plains
Dryland farmers in the semiarid Central Great Plains have used summer fallow to move from a full-season summer crop to winter wheat, but there is interest in eliminating summer fallow, which is a direct cost to the enterprise. Lyon et al. (855–860) established a summer fallow treatment and five spring crops (spring canola, oat + pea for forage, proso millet, dry bean, and corn) that were no-till seeded into sunflower residue in 1999, 2000, and 2001. Winter wheat was planted in the fall following the spring crops. Systems involving oat + pea for forage and proso millet were economically competitive with systems using summer fallow.
DNA Fingerprinting Cultivar Enola
Since a 1980 Supreme Court decision, it is possible in the USA to obtain a utility patent for crop cultivars and other life forms. Furthermore, it is also possible to obtain Plant Variety Protection for cultivars. Using DNA fingerprinting by amplified fragment length polymorphism, Pallottini et al. (968–977) show that the patented yellow bean cultivar Enola is closely related, if not identical, to Mexican yellow bean cultivars, such as Azufrado Peruano 87.
Cross-Pollination in Forage Grasses
Progress from selection for increased forage yield of most cross-pollinated forage grass species has been modest, despite long-term efforts of different forage breeding projects. Inbreeding has been used successfully in maize (Zea mays L.) and several other cross-pollinated species to help identify superior parents, but this procedure has had very limited use in breeding forage grasses. Berdahl and Ray (768–771) subjected 20 common plants from each of three distinct crested wheatgrass (Agropyron spp.) populations to self-pollination and open-pollination. Progenies from the self-pollinated and open-pollinated plants were equally effective in identifying superior parents for experimental strains. This information is critical in choosing efficient breeding methods for crested wheatgrass.
Methods for Testing Resistance to Sclerotinia sclerotiorum
Many inoculation methods have been used to evaluate resistance of different crops to the fungal pathogen, Sclerotinia sclerotiorum (Lib.) de Bary. A single greenhouse inoculation method has not been used across crops and compared with field evaluations. Vuong et al. (777–783) compared disease evaluations of soybean [Glycine max (L.) Merr.], dry bean (Phaseolus vulgaris L.), and sunflower (Helianthus annuus L.) inoculated in the greenhouse (cut stem inoculation method) with field evaluations. Within each crop, there was a correlation between disease assessments from the cut stem inoculation method and field evaluations. In summary, the cut stem inoculation method has the potential for use in evaluating soybean, dry bean, and sunflower for resistance to S. sclerotiorum.
Salt Tolerance in Sorghum
Saline soils have been a great impediment to crop production in the tropics. Sorghum bicolor (L.) Moench is a tropical crop that has undergone breeding and limited adaptation to saline soils. Netondo et al. (797–805 and 806–811) give a comprehensive account of the physiological responses of the crop to NaCl salinity. Two improved, salt tolerant varieties of sorghum, Serena and Seredo, were grown in Kenya. Tissue ion accumulation and fluorescent measurements were conducted. Salinity had a negative effect on sorghum growth with increasing salt content in the growth media, but the two cultivars did not show any constitutive difference in either vegetative growth or fluorescent measurements. Sodium chloride also affected the absorption of nutritional ions K+, Ca2+, and Mg2+, which could have caused deficiencies and metabolic perturbations. Further studies measured the gas exchange parameters CO2 assimilation, transpiration rate, internal CO2 concentration, and stomatal conductance, and measurements of chlorophyll fluorescence established the extent of damage to the photosynthetic apparatus by salt. Salinity affected the photosynthetic processes of both varieties similarly and the effect at high salinities (200 and 250 mM) could have involved damage to the photosynthetic apparatus. The study should be useful in understanding the physiological effects of NaCl on sorghum and in developing productive cultivars for saline soils of the tropics.
Doubled Haploid Procedure in Transgenic Cultivar Breeding Programs
Tang et al. (732–740) assessed the expression stability of acyl-acyl carrier protein (ACP) thioesterase (TE) transgenes in oilseed rape (Brassica napus L.), doubled haploid (DH) lines, developed from microspores of F1 plants from the crosses between transgenic parents carrying the bay-TE (Uc FatB1), elm-TE (Ua FatB1), nutmeg-TE (Mf FatB1), or cuphea-TE (Ch FatB1) transgenes and three nontransgenic cultivars having distinct seed oil fatty acid compositions. No DH1 plant with completely silenced TE transgenes was detected. The stability of expression was excellent, with 30 of 34 transgenic DH lines showing a stable level of the target fatty acid, lauric for the bay-TE and palmitic for the other three TE transgenes, over the two or three consecutive generations tested (DH2, DH3, and/or DH4 plants). Target fatty acids were significantly affected by temperature during seed development. These results support the application of the DH procedure in breeding programs for transgenic cultivars and indicate the important influence of environment.
Phosphorus Concentration in Maize
The total phosphorus concentration in maize (Zea mays L.) grain exceeds the phosphorus requirement in a finishing cattle (Bos Taurus) ration. Wardyn and Russell (753–757) conducted an experiment to determine the amount of genetic and nongenetic variation for phosphorus concentration in the grain of a maize population cross. Significant genetic variation, both within and among S1 families, as well as significant nongenetic variation for phosphorus concentration was found. The loss of efficiency from basing selections on 1 yr of data rather than 2 yr was estimated at 5%. The results provide a guideline for initiation of a selection program for phosphorus concentration in maize.
Soybean Cyst Nematode Resistance QTL
Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is one of the most destructive soybean [Glycine max (L.) Merr.] pests worldwide. The most commonly used source of SCN resistance in the midwestern USA is PI 88788, which is known to carry the major SCN resistance quantitative trait locus (QTL) rhg1. Glover et al. (936–941) mapped an additional QTL from PI 88788 and confirmed its presence in populations of near isogenic lines (NILs). The effect of the QTL in the NIL populations was less than in the original mapping population. This diminished effect was at least partially the result of segregation distortion between the region containing rhg1 and the region containing the new QTL in the original population.
Row Width Affects Cotton Canopy Microclimate
Canopy microclimate determines the rate of fruit development, pest pressure, and crop response to ambient conditions. Marois et al. (870–877) studied canopy microclimate in UNR cotton (Gossypium hirsutum L.) (18- to 25-cm row width) and conventional (76- to 91-cm row width) plantings with low N (16.8 kg ha–1 at planting only) or high N (16.8 kg ha–1 at planting and 202 kg ha–1 3 wk after bloom) fertilizer was quantified by monitoring the plant canopy temperature, relative humidity (RH), and vapor pressure deficit (VPD) every 15 min during the growing season. During the hours from 0700 to 1900, temperature was 1 to 2°C higher and RH 3 to 7% lower in the conventional vs. the UNR plantings. In general, N and row width effects did not have as great an impact on canopy microclimate as did plant height.
PCR Assay Tests Purity of Rice Parental Line Seed Stocks
The cytoplasmic male sterile (CMS) lines that are utilized for developing the commercial three-line rice (Oryza sativa L.) hybrids often get contaminated with their isonuclear maintainer lines during CMS line multiplication. A DNA sequence that is homologous to rice mitochondrial DNA, but unique to the Wild Abortive (WA) CMS lines of rice, has been identified by Yashitola et al. (920–924). Oligonucleotide primers based on this unique DNA sequence could be used in a PCR assay to detect contamination of maintainer seeds in stocks of the WA-CMS line. This assay is rapid, reliable, and may substitute the conventional grow-out test for assessing the purity of parental lines used in hybrid rice production.
Morphological Marker for Wheat Spot Blotch Disease Resistance
To date, no morphological marker is known for resistance to spot blotch disease of wheat (Triticum aestivum L.) caused by Bipolaris sorokiniana (Sacc.) Shoemaker. When Joshi et al. (792–796) evaluated 1407 spring wheat genotypes for leaf tip necrosis (Ltn) and spot blotch, mean disease rating of the Ltn+ genotypes was significantly lower than the Ltn– genotypes. To confirm this association, individual F2–derived F3, F4, F5, and F6 progenies from the cross of the ‘HUW234’ near-isogenic pair for Ltn were evaluated. In each generation, the Ltn+ homozygous progenies had significantly less disease than those homozygous Ltn–. It is suggested that Ltn can be used as a morphological marker to facilitate selection for resistance.
Medicago truncatula Response to Salinity
Knowledge of a plant's response to salinity, which may or may not involve a unique physiological response, is important in determining the most efficient method of increasing yield under salt stress. Veatch et al. (1008–1013) evaluated yield of greenhouse grown mature plants and seedlings of different genotypes of Medicago truncatula Gaertn. exposed to four salinities from 0 to 115 mM NaCl. Those genotypes with the highest yield under low salinity had the highest yield under the higher salinities. The correlation between yield under low and high salinity indicate no unique physiological adaptation to salinity in M. truncatula.
Weed Management in Catnip and St. John's Wort
Opportunities have increased for medicinal herb production in the USA, but there is limited information on production practices. Duppong et al. (861–869) conducted a weed management experiment to examine the effect of no weeding, hand-weeding, oat straw, flax straw mats, and wool mats in the production of catnip (Nepeta cataria L.) and St. John's wort (Hypericum perforatum L.). Fewer weeds developed in the flax straw and wool mat treatments in each crop over two years compared to positive control plots. There was a trend toward higher concentrations of hypericin in St. John's wort in the flax straw treatment and no negative effect on nepetalactone content in catnip.
Lolium Reference Genetic Map
A number of analytical methods have been used to detect quantitative trait loci (QTLs) for a number of agronomic traits of the important pasture grass species perennial ryegrass (Lolium perenne L.). The reference genetic map constructed through the efforts of the International Lolium Genome Initiative (LLGI) was enhanced by Yamada et al. (925–935) using simple sequence repeat (SSR) markers, and phenotypic data were obtained for a number of field-assessed morphological, developmental, and winter hardiness traits. Coincident QTLs on several linkage groups were detected for a range of morphogenetic characters. This study provides the basis for marker-assisted selection (MAS) of important agronomic characters, allowing genetic improvement of yield, quality, and adaptation in perennial ryegrass breeding.
Wheat Tsn1 Region
Tan spot is a foliar disease of wheat (Triticum aestivum L.) caused by the fungus Pyrenophora tritici-repentis (Died.) Drechs., which produces a proteinaceous necrosis-inducing toxin. Sensitivity to the toxin is controlled by a single gene in the host designated as Tsn1. Using various molecular methodologies in combination with wheat cytogenetic stocks, Haen et al. (951–962) saturated the Tsn1 region with molecular markers, constructed high resolution maps of the Tsn1 region, and delineated the gene to a 0.8-cM segment. Comparisons with rice genomic sequences indicated a lack of colinearity within the region. This work provides the basis for the cloning of the Tsn1 gene, which will provide knowledge regarding host–toxin interactions.
Lemma/Palea Are Protective Structures
The lemma and palea (lemma/palea) of cereals are photosynthetic organs that eventually form the seed husk. To examine gene expression patterns in the barley (Hordeum vulgare L.) lemma/palea, Abebe et al. (942–950) constructed subtracted cDNA libraries from three developmental stages using the lemma/palea as tester and the flag leaf as driver. Differential screening and northern hybridization confirmed that the clones represent mRNAs that were highly expressed in the lemma/palea, compared with the flag leaf. Sequence analysis of 226 clones identified a high proportion of genes for defense, structure, amino acid biosynthesis, and photosynthesis, suggesting that the lemma/palea are protective structures that also serve as major sources of nitrogen and carbon for the developing kernel.
Increased Transgene Expression in White Clover
Phenotypic recurrent selection was used to select for increased transgene expression in white clover, Trifolium repens L. Schmidt et al. (963–967) transformed plants with nptII and selected on 100 mg L–1 kanamycin. With selection on increasing levels of kanamycin, average expression went from 0.033 ng µg–1 NPTII in the parents to 0.095 ng µg–1 in the selected T1 plants to 0.539 ng µg–1 in the selected T2 plants. Selected plants were of one particular transgenic event, implicating other genomic factors in modulating gene expression. A second set of selected plants had an accumulation of transgenic loci, suggesting an association between multiple transgene copies and high expression levels.
Maize Infestation of Pink Stem Borer
Yield under infestation by the pink stem borer (Sesamia nonagrioides Lef.) (PSB) has been proposed as the best estimator of maize (Zea mays L.) performance under PSB attack, but yield is a complex trait that greatly interacts with the environment. Butrón et al. (741–747) studied the genotype x environment (GE) interaction for yield of maize hybrids in five environments, with different levels of infestation, by the site regression (SREG) and factorial regression methods. Hybrid A637 x EP42 is recommended in northwestern Spain under medium and high natural infestation of PSB because it showed high and stable yielding ability. In general, GE effects for grain yield were mainly due to earliness, vigor effects, and environmental yield limiting factors such as the mean of minimum temperature and percentage of air humidity.
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 |
||||
