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A field trial was undertaken by Leibbrandt and Snyman (p. 671–677) to assess transgene stability and agronomic performance of transgenic herbicide-resistant (Buster: glufosinate ammonium) sugarcane (Saccharum hybrid). A comparison of stalk characteristics and response to pests and diseases between transformed and untransformed sugarcane showed no significant changes in the genetically engineered plants. Favorable sucrose yields were observed in transgenic sugarcane treated with a conventional preemergence herbicide cocktail, followed by Buster application. However, the economic advantage of this weed control method is dependent on the pricing of the herbicide.
Intraspecific Gene Flow in Wheat
Accurate gene flow estimates between bread wheat (Triticum aestivum L.) cultivars are necessary to establish guidelines for isolation distance, especially when genetically modified wheat cultivars are being developed. Rigorous gene flow studies are absent from the literature, yet predictions about wheat gene flow can be made based on the existing outcrossing data. Although outcrossing rates appear to be very low in wheat because of the selfing nature of the wheat flower, outcrossing rates vary substantially depending on wheat cultivars and environmental conditions. Therefore, the following three components may be considered while developing isolation distances for wheat cultivation: cultivar genotype, environmental conditions during flowering, and the acceptable level of contamination (p. 451–463).
Soybean Seed Cell Polysaccharide, Yield, and Seed Trait Relationships
Soybean seed [Glycine max (L.) Merr.] cell wall polysaccharides (CWP) are complex structures representing a significant carbon sink which may be correlated with other traits like protein, oil, and yield. Stombaugh et al. (p. 571–576) have used principal component analysis to simplify CWP variability into clusters or components and to relate these components to seed traits. Pectin polysaccharides were negatively correlated with the sum of protein and oil. Cellulose, hemicellulose, and arabinose were negatively correlated with yield. Seed weight was related to specific components as well. Principal component analysis defined which polysaccharides varied with seed traits.
Lime Addition to Soils for Red Clover Seed Production
Can addition of lime increase soil pH levels and reduce the amount of root rot found in red clover (Trifolium pratense L.) seed production fields? If so, seed yields and the stand life of red clover seed fields could be increased, which would amortize establishment costs and increase net profit to farmers. The effects of lime applications, herbage removal timing, and stand age on the economic yield of red clover seed was looked at in the maritime Pacific Northwest by Steiner and Alderman (p. 624–630). First year seed yield was increased by lime, but second year seed yield was not. Although first year income increased with increasing lime amount, second seed year income decreased, so two-year combined income was unaffected. Interestingly, root rot incidence increased with increases in soil pH that is opposite to reports for other crops. When the added expense for adding lime is considered, there was no benefit from lime. Since there was also no benefit from lime on the following wheat rotation crop, lime application cannot be justified solely for the benefit of red clover seed production.
Wheat-Rye Translocations of Chromosomes 1 and 2 in Spring Bread Wheat ‘Pavon’
Increased root biomass may be the morphological basis of the 7% mean higher grain yield of wheat (Triticum aestivum L.) cultivars with the 1RS.1BL wheat-rye translocation. Ehdaie et al. (p. 710–717) report an isochromosomal series for 1RS from ‘Kavkaz’ wheat in ‘Pavon’ spring wheat that always had increased root biomass. There was a consistent position effect with 1RS.1Al > 1RS.1DL > 1RS.1BL > Pavon for root biomass and grain yield in well-watered and drought-stressed pot studies. In field studies, the 1RS.1AL translocation had 20% increased grain yield compared with Pavon. Root biomass may be important for grain yield increase.
Seed Abortion and Reproductive Trait Genetics in Soybean
Recombinant inbred (RI) segregants of soybean [Glycine max (L.) Merr.] were used by Tischner et al. (p. 464–473) to identify quantitative trait loci (QTLs) that regulate different parameters of seed set. The numbers of ovules per pod and abortions were measured, as were positions and developmental stages of abortions within pods. Quantitative trait loci were found on several linkage groups, including U11, U13, and U22. They were linked to QTLs for flowering date, reproductive period, maturity, male and female sterility (Ms1, Ms6, or St5), disease resistance, water use efficiency, and to Lf1 (suggesting a common regulation of leaf and flower primordia).
Simultaneous Improvement of Orchardgrass Forage and Seed
Orchardgrass (Dactylis glomerata L.) has two commodities, forage and seed, that are produced in contrasting environments. Simultaneous improvement of both commodities in a single breeding program is highly problematic because of geographic separation of these environments. Casler et al. (p. 532–538) showed that even the most comprehensive efforts to utilize sophisticated multilocation selection protocols to improve seed yield were less efficient than selection within the target population of environments. They also showed that selection for seed yield within the target population of environments did not result in improvements in forage yield. The most efficient simultaneous selection for forage and seed traits will require use of both types of environments.
Root Developmental and Functional Patterns
Nationally and internationally, soil-based constraints to productivity are a significant challenge to agriculture. In the Appalachian region of the USA, crop and pasture productivity is inhibited by many soil-based problems. An understanding of root growth and function in pastures of this region will lead to adoption of management strategies that can alleviate some or all of these difficulties. Previous technology did not allow easy estimation of the finest (thinnest) roots, which are also the most important in terms of root function. Zobel (p. 583–591) describes research that demonstrates that an adjustment of digital root images allows current software and technology to measure accurately all sizes of root. The research also demonstrated that digital camera and digital scanner technologies are equivalent in their ability to image the thinnest roots. These techniques greatly improve our ability to acquire knowledge of root developmental and functional patterns in the Appalachian Region and worldwide.
Genes Regulated by Drought and Salinity Stress
Drought and high salinity limit plant growth and crop production worldwide. Knowledge of the molecular mechanisms underlying the response to these abiotic stresses is important for an understanding of stress tolerance and for germplasm improvement. Using differential mRNA display and quantitative RT-PCR, Liu and Baird (p. 678–687) identified 13 genes regulated by drought and/or salinity stress. Their individual expression patterns defined three regulation categories and suggest cross-talk between signal transduction pathways during osmotic stress response.
Improved Winter Hardiness in Alfalfa
Large differences in winter hardiness exist among alfalfa (Medicago sativa L.) cultivars, but the physiological and molecular bases for these differences are not understood. Cunningham et al. (p. 562–570) isolated and characterized a cDNA for galactinol synthase (GaS), a key enzyme in the synthesis of raffinose and stachyose, two sugars associated with improved winter hardiness. High raffinose and stachyose levels and elevated expression of GaS occurred in autumn, and these were consistently associated with genetic variation in winter survival. Understanding the mechanisms regulating GaS gene expression in roots and crowns during autumn may provide opportunity to genetically improve alfalfa winter hardiness.
Genetic Variation in Creeping Bentgrass Populations
Creeping bentgrass (Agrostis stolonifera L.) is one of the most important cool-season grasses for golf courses. Old golf courses contain numerous creeping bentgrass plants that appear to have survived many years of natural selection. Little is known about genetic variation among and within creeping bentgrass populations on long-term golf courses. Casler et al. (p. 688–693) found considerable variation in RAPD (random amplified polymorphic DNA) markers among creeping bentgrass clones collected from golf courses fairways. Much of this variation could be attributed to differences in presettlement vegetation of northern Wisconsin, causing differential pH and organic matter. Clones collected from putting greens were not differentiated by golf courses, suggesting that the putting green environment was sufficiently homogeneous across golf courses that its impact on natural selection was uniform.
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