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Earlier spring planting to maximize the duration of the growing season has increased the importance of early-season cold tolerance in maize (Zea mays L.). Lee et al. (p. 1919–1929) investigated the effects of low temperature on several physiological parameters on 49 inbred lines: carbon exchange rate, leaf chlorophyll content, quantum efficiency of Photosystem II, leaf conductance, dry weight, root/shoot ratio, and rate of development. The low temperature effects were significant for all parameters except root/shoot ratio. Genetic diversity for most traits investigated was observed for the response of the inbred lines to low temperatures. Results of this study show that leaf carbon exchange rate and rate of development are good discriminators of cold tolerance during early phases of development.
Condensed Tannin Concentration in Roundhead Lespedeza
Roundhead lespedeza, Lespedeza capitata Michx., is a deep-rooted, perennial legume native to the eastern and central USA and is relatively common on remnant upland prairies throughout the Midwest. Information on condensed tannin (CT) concentration from different plant parts of available germplasm is needed for cultivar development and also to provide data for developing management and feeding strategies. Springer et al. (p. 2157–2160) analyzed the CT concentration from leaves, stems, and inflorescences from 39 roundhead lespedeza plant introductions grown in two environments. Variation due to environment was low, variation due to genotype was high, and variation due to genotype x environment interaction was high. Of these 39 plant introductions, we selected eight that were common to both environments that had low CT concentrations in leaves at flowering. The CT content of these plant introductions, however, was still relatively high when compared with other Lespedeza species that were bred for low tannin content.
Lignin, EthFA, and Forage Digestibility
Selection for reduced lignin or etherified ferulic acid (EthFA) concentration may be mechanisms for increasing digestibility of forage crops. Delgado et al. (p. 1824–1831) used smooth bromegrass (Bromus inermis Leyss.) genotypes, divergently selection for lignin or EthFA concentration, to test the hypothesis that reduced lignification and/or ferulate cross-linking may impair host resistance to fungal pathogens. Numerous associations were observed, but most appeared to be random, suggesting gametic phase disequilibrium or linkage disequilibrium as a genetic cause. However, low lignin concentration was consistently associated with susceptibility to crown rust (caused by Puccinia coronata), paralleling results from other grasses, and suggesting a potential causal relationship.
Six Annual Ryegrass Cultivars Compared for Forage Value
Differences among annual ryegrass (Lolium multiflorum Lam.) cultivars for weight gain of grazing steers have been reported, even though plot experiments suggest that forage dry matter yield among cultivars should not be a limiting factor. Redfearn et al. (p. 2049–2054) evaluated differences in cumulative forage yield, seasonal yield distribution, and nutritive value among six annual ryegrass cultivars. There were no differences among cultivars for cumulative forage yield, but there were differences in the seasonal distribution. There was a general decline in nutritive value as the growing season progressed. There were differences in maturity, which resulted in nutritive value differences among cultivars later in the growing season. Our results suggest that seasonal yield distribution in response to maturity and nutritive value may contribute to differing animal responses among annual ryegrass cultivars.
Optimum Sowing Date for Cuphea in West Central Minnesota
Cuphea, a plant whose seed is rich in medium-chain fatty acids (C:8–C:14), is being developed as a domestic replacement source for coconut and palm kernel oils. Gesch and coworkers (p. 1959–1965) conducted a study in 1999 and 2000 to determine the optimum sowing date for Cuphea (cv. PSR23) in west central Minnesota. Cuphea has an indeterminate growth habit and it responded to sowing date similarly to other crops such as soybean and dry bean, which also have such a growth type. Sowing in early to mid-May resulted in greatest seed and seed-oil yields and there was a distinct decline in plant biomass and seed yield when planting was delayed until June.
Herbicide-Resistant Genes in Jointed Goatgrass from Commercial Wheat
Jointed goatgrass (Aegilops cylindrica Host) currently infests more than 3 million hectares of winter wheat cropland in the USA. This wild relative of wheat (Triticum aestivum L.) forms hybrids with wheat that could result in the movement of herbicide-resistant genes from commercial wheat into jointed goatgrass. Morrison and coworkers (p. 1863–1872) conducted a study in the dryland wheat region of Oregon as a preliminary step in understanding this phenomenon. Collections of hybrids from infested fields were evaluated to determine parentage. Maternal seed remains found among the roots of hybrid plants showed that jointed goatgrass was usually the F1 hybrid parent; glutenin protein markers found in seed endosperm showed that wheat was most often the pollen parent of backcross seed produced on these F1 plants. This work suggests that development of a jointed goatgrass-like hybrid carrying wheat genes would depend on the presence of persistent weed populations where backcross hybridizations to jointed goatgrass could repeatedly occur.
Genetic Diversity in Cotton Germplasm
Knowledge of genetic diversity in cotton (Gossypium hirsutum L.) germplasm can have a significant impact on crop improvement, however such information is limited. Gutiérrez et al. (p. 1841–1847) fingerprinted 11 cotton genotypes with 90 SSR primers pairs which provided 69 polymorphic marker loci and investigated the association between genetic distance and F2-bulk population performance. Genetic distance values based on SSR markers exposed the lack of genetic diversity among all genotypes and were poor predictors of heterosis. Performance of F2-bulk populations does not depend only on genetic diversity, but also on the genetic background and environmental effects.
Artificial Drying of Maize and Decreased Germination, Vigor
The impairment of lipid body (LB) alignment along the plasma membrane during artificial drying of maize (Zea mays L.) seed has been association with decreases in germination and vigor. Cordova-Tellez and Burris (p. 1982–1988) question further its potential functions as well as the alignment mechanisms. Alignment of LB along the plasma membrane is a progressive process that occurs from the periphery to the inner quiescent center cells of the embryo radicle during the acquisition of desiccation tolerance. Alignment of LB along the plasma membrane may change cell water relations leading to a more organized dehydration during seed drying. High embryo drying rates may prevent alignment of LB along the plasma membrane and are associated with low germination and vigor.
Moisture Content and Drying Rates of Maize Seed
Maize (Zea mays L.) seed quality is often reduced because of drying injury, although the causes and impairment mechanisms are poorly understood. Cordova-Tellez and Burris (p. 1989–1995) investigated changes in embryo drying rates and their effect on the acquisition of desiccation tolerance in maize seed using preconditioning (PC, slow drying) before fast drying or fluidized bed (FB) drying treatments. As embryo moisture content declined to 400 g H2O kg-1 fresh weight at slower drying rates, either with PC or field drying, the ability to withstand the faster drying rates of the FB progressively increased. This was reflected in lower cell solute leakage, better germination, and vigor.
P Uptake and Concentration in Timothy under Varying N
Improving P uptake in timothy (Phleum pratense L.) would reduce excess soil phosphate while producing forage with greater P nutritional value. Bélanger et al. (p. 2044–2048) studied two timothy populations derived from divergent selection for high and low forage N concentration along with seven half-sib families identified in a field study as having contrasting DM yield and N concentration. Timothy genotypes, under conditions of nonlimiting P availability, differed in P concentration and uptake for forage and total biomass. This genetic variation in P uptake and concentration was related to genotypic differences in DM yield, leaf P concentration, the proportion of leaves in the forage, and the proportion of roots in the total biomass.
N Effects on Septoria Leaf Blotch in Wheat
Nitrogen fertilization is required for achieving high yields in wheat (Triticum aestivum L.), but may enhance the development of leaf blotch (caused by Septoria tritici Rob. ex Desm.) under conducive conditions. Simón et al. (p. 1974–1981) investigated how Septoria leaf blotch under different N supplies affects yield, yield components, and test weight. Two field trials with two inoculation treatments, two N-fertilization conditions, and seven cultivars were carried out in a split plot design in two years. Reduction in yield, yield components, and test weight due to Septoria leaf blotch were similar in fertilized and nonfertilized conditions, despite the significant increase in AUDPC (area under disease progress curve) values by N fertilization in one of the years. Cultivar specific effects on AUDPC values were not always consistent with yield reduction effects, suggesting cultivar differences in tolerance.
Light Effects on Redroot Pigweed Development
Both light quantity and quality may affect phenological development of weed species. Rajcan et al. (p. 1930–1936) conducted an indoor study to quantify the effects of incident photosynthetic photon flux density (PPFD) and red:far-red (R:FR) ratio on development and dry matter accumulation of redroot pigweed (Amaranthus retroflexus L.). Rate of development of redroot pigweed was reduced at low PPFD and high R:FR ratio compared with high PPFD and high R:FR treatment. In addition, only at 12-h daylength, the FR enrichment (low R:FR ratio) accelerated the development of redroot pigweed under low PPFD. Results of this study show that growth and development of redroot pigweed are influenced by both quantity and quality of incident light.
Narrow-Leaf Plantain and Chicory for Forage
Cultivars of new forage species must be adapted to local conditions before they can be introduced into pasture production systems. Skinner and Gustine (p. 2038–2043) investigated the freezing tolerance and winter survival of ‘Ceres Tonic’ and ‘Grasslands Lancelot’ narrow-leaf plantain (Plantago lanceolata L.) and ‘Grasslands Puna’ chicory (Cichorium intybus L.) which have been considered for inclusion in northeastern USA pastures. Chicory had acceptable freezing tolerance, but neither plantain cultivar was sufficiently winter hardy to survive northeastern USA conditions. Drought stress during the summer tended to increase freezing tolerance. Improved cultivars will need to be developed from populations that have evolved under more severe winter conditions before plantain can become a viable forage for most of this region.
Screening for Cucumber Yield and Quality
Shetty and Wehner (p. 2174–2183) have used efficient field testing methods to screen the USDA germplasm collection for early, total, and marketable yield. In order to help plant breeders make the best use of the new germplasm, they have also rated the fruit for quality and classified each accession by type. The germplasm collection of 810 diverse accessions can be grouped into pickling, slicing, middle-eastern, and oriental trellis types. Accessions with high yield were identified within each of the cucumber types, which should be useful for plant breeders interested in new sources of high-yielding germplasm for their cucumber improvement programs.
Improvement in Adaptability and Yield in Grasses
As the grass family emerges as a single genetic system, opportunities for improvements of grass-based grain crops are increasing dramatically. Findings in Sorghum bicolor (L.) Moench and several other crops on flowering, maturity, the biological clock, responses to shading, apical dominance, and plant architecture are suggesting specific strategies for improvement of many monocotyle-donous crops. See Morgan et al. (p. 1791–1799).
Membrane Polar Lipid Fatty Acids of Seashore Paspalum
Seashore paspalum (Paspalum vaginatum Sw.) is subject to winter injury within its zone of adaptation. Cyril et al. (p. 2031–2037) used thin layer chromatography and high-pressure liquid chromatography analyses to characterize the degree of fatty acid saturation in membrane lipids. Four major fatty acids were identified. During low temperature exposure, significant increases in the tri-unsaturated linolenic acid (C18:3) occurred at the expense of linoleic acid (C18:2). These changes occurred to a greater extent in ‘Sea Isle 1’, a fine-textured relatively cold-tolerant cultivar, than they did in ‘Adalayd’ or PI 299042, more cold-sensitive genotypes. This information is useful for evaluating other genotypes and in the improvement of existing germplasm for greater cold tolerance through selection, breeding, and biotechnology.
Related articles in Crop Science:
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