| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Grass tetany has caused severe economic losses in ruminant animals grazing cool-season grasses. Asay et al. (1478–1484) evaluated the genetic variability and genotype by environment interactions for characteristics associated with grass tetany and forage quality in 21 clonal lines of Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] and their polycross progenies at three diverse semiarid locations. Although the genotype x location interactions were usually significant, the results suggested that selection for reduced grass tetany potential and improved forage quality based on data combined across locations would be a feasible approach in this breeding population.
Fusarium Wilt and Marker-Assisted Selection in Common Bean
Fusarium wilt of common bean (Phaseolus vulgaris L.) is an increasing problem in the western USA, and genetic resistance is considered the most feasible control method. Using quantitative trait locus analysis, Fall et al. (1494–1498) detected a major locus for controlling resistance to the disease, the first time a locus for this trait has been mapped in bean. The locus accounted for 64% of the phenotypic variation for disease severity. The close linkage between the locus and a DNA marker suggests that marker-assisted selection may be used effectively in development of Fusarium wilt resistant common bean cultivars.
Genetically Modified Crops and QC Monitoring
Safety concerns and labeling requirements for genetically modified crops have imposed unprecedented Quality Control (QC) demands on the seed industry. The goal of QC monitoring in Transgenic Seed Product Development (TSPD) is to protect research investments and ensure government regulatory compliance by monitoring transgenic event identity and seed purity in product testing. QC strategies formulated for the manufacturing industry can form a foundation for strategies tailored to the needs of the seed industry. Design of QC monitoring plans for TSPD are discussed by Mumm and Walters (1381–1389), including QC costs versus benefits, timing of inspections; assay methods, sampling strategies; sample pooling, and impact of inspection errors. An example QC monitoring strategy is provided.
Switchgrass Seed Dormancy Reversal
Switchgrass (Panicum virgatum L.) often fail because of seed dormancy; the seeds are viable but will not germinate when planted into warm soils. Farmers can stratify seeds (expose wet seeds to cool temperatures) to break their dormancy, but studies at Virginia Tech have shown that as stratified seeds dry, dormancy may return. To avoid this post-drying "reversion" to a dormant state, the seeds often must be stratified for up to 6 wk. Alternatively, seeds that have been "afterripened" (had an extended period of warm, dry storage) may become completely nondormant (Shen et al., 1546–1551). At the least, afterripened seeds are less likely to revert to dormancy following stratification. Because commercial seed labs typically test switchgrass using conditions that cause stratification (and therefore fail to detect dormancy), growers should test switchgrass seeds for germination using nonstratifying conditions. If the seeds need to be stratified, stratification should be for at least 6 wk to prevent them from reverting to a dormant state upon drying.
Soybean Flower Abortion
A large proportion of flowers in the soybean plant [Glycine max (L.) Merr.] abort during development. Water stress imposed during the development of flowers is a major factor increasing the abortion rate, and long-term or frequent water deficits might decrease the yield. The physiological mechanism underlying this phenomenon remains unclear. Kokubun et al. (1517–1521) investigated whether a water deficit imposed on soybean prior to anthesis caused abortion of the proximal flowers, which are destined to grow pods at a high rate under optimal conditions, and whether the abortion was due to the impairment of the pistil (ovule) or stamen (pollen) function. Restriction of watering for 3 d during the preanthesis stage significantly increased abortion of proximal flowers. Our results suggest that flower abortion caused by a preanthesis water deficit is not attributed to an impairment of pollen, but probably due to impairment of ovule function.
Chromosome Numbers in Smooth Bromegrass
Smooth bromegrass (Bromus inermis Leyss) is one of the most widely grown cool-season forage grasses in the North America. Reported chromosome numbers of smooth bromegrass and related species range from 14 (diploid) to 70 (decaploid). The U.S. Department of Agriculture has over 300 accessions of these grasses in its National Plant Germplasm System. The chromosome numbers of most of these accessions were unknown which restricted their use by plant breeders. Tuna and coworker (1629–1634) determined chromosome numbers of over 300 bromegrass accessions in the USDA Plant Germplasm System by measuring cellular DNA content by flow cytometry and then relating DNA content to chromosome number of specific accessions. The chromosome numbers of accessions of smooth bromegrass and related species is now available on the USDA's National Plant Germplasm Systems GRIN database.
Timothy in Grazing Systems
Cultivated timothy (Phleum pratense L.) germplasm has potential value for rotational grazing systems in North America. Casler (1616–1624) evaluated 482 accessions of cultivated timothy plus 36 accessions of other Phleum species for forage yield and persistence under frequent defoliation, morphological characters, and seed production traits. Cultivated accessions showed considerable differences from natural accessions, including higher forage yield and lower persistence under frequent defoliation. Accessions of the diploid and tetraploid species were generally similar in performance to accessions of cultivated hexaploid timothy. Much of the phenotypic variation within the collection could be explained by geographic source of the accessions. The experiment identified a structure for a core subset of timothy accessions and several accessions that should have value for timothy breeding.
Molecular Markers in Tomato
Marker-assisted selection provides an opportunity to improve the efficiency of traditional breeding methods for carotenoid content in tomato (Lycopersicon esculentum Mill.) fruit. Zhang and Stommel (1602–1608) developed molecular markers in tomato linked to the dominant Beta locus which influences accumulation of high levels of fruit ß-carotene. Random amplified polymorphic DNA (RAPD) markers linked to Beta were cloned and sequenced and the sequence information utilized to develop two codominant cleaved amplified polymorphic sequence (CAPS) markers and a dominant sequence characterized amplified region (SCAR) marker linked to this locus. These markers may be utilized in marker-assisted breeding for tracking the introgression of B into breeding lines, selection at early seedling stages of development, and efficient identification of true breeding genotypes during development of adapted tomato germplasm with increased ß-carotene content and nutritional value.
Forage Yield of Smooth Bromegrass
Smooth bromegrass (Bromus inermis Leyss) cultivars have shown inconsistent forage yield ranking across a wide range of geographic locations. Casler et al. (1456–1460) showed that cultivars could be clustered into groups that reflect differential mean performance as well as differential adaptation among zones within the target region. Geographically defined zones differed largely in degree and pattern of temperature and rainfall (e.g., dryland vs. high rainfall, mild vs. severe winters). Much of the geographic grouping of cultivars could be explained by pedigree, selection history, or selection location. However, there were some homogenous groups that consisted of divergent pedigrees and selection locations, suggesting a possible widespread distribution of alleles for high and stable forage yield of smooth bromegrass.
Switchgrass Genetics and Breeding Programs
The genetic relationship of the two major ecotypes of switchgrass (Panicum virgatum L.) and the inheritance of chloroplast DNA needed to be clarified for effective use of switchgrass germplasm in breeding programs. Martínez-Reyna and coworkers (1579–1583) used plants from upland tetraploid cultivar Summer and lowland tetraploid cultivar Kanlow in conventional, cytogenetic, and molecular marker studies. They determined that meiotic chromosome pairing was normal for the hybrids, indicating that the two ecotypes have the same genome. Chloroplast DNA markers indicated that chloroplast inheritance in switchgrass is maternal. Breeders should be able to effectively use both upland and lowland germplasm sources in switchgrass improvement 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 | |||
