bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heterosis Decreasing in Hybrids: Yield Test Inbreds
Authors: Troyer A. Forrest , Wellin Eric J. 
Published: October 2009

ABSTRACTYield testing finished inbreds to replace preliminary single‐cross corn (Zea mays L.) yield tests will increase rate of commercial hybrid yield gains. Studies have shown that heterosis decreased 25%/50 yr, 10%/60 yr, and 35%/100 yr. Natural selection and artificial selection by plant breeders for adaptedness have increased parental inbred and hybrid seed yields, whereas percentage heterosis decreased. Four studies have shown inbred yields increased 1.9 to 3.5 times faster than heterosis yields. Pioneer Hi‐Bred generates 700 new inbreds tested in 6000 single‐cross hybrids at 15 to 20 locations annually. Predicted, untested, newer hybrids are then made and tested extensively with commercial hybrids. Parental inbred yield testing is the next to last of several steps in hybrid development. Commercial hybrid development costs have increased logarithmically, whereas performance has increased linearly. Replacing preliminary testcross trials with finished‐inbred yield trials is more efficient. About 12,000 new finished inbreds can be evaluated annually with no testers and at least 50% fewer locations per inbred with the same testing effort as 700 new inbreds with testers. A calendar year per breeding cycle and annual production costs for 6000 hybrids will be saved. Corn yield trials detect stress susceptibility, which is more apparent in inbreds than in hybrids. Evaluation of more new inbreds will be conducive to increased genetic diversity that produces higher‐yielding hybrids.
Genotype × Environment Interactions of Hybrid and Varietal Rice Cultivars for Grain Yield and Milling Quality
Authors: Blanche Sterling B. , Utomo Herry S. , Wenefrida Ida , Myers Gerald O. 
Published: October 2009

ABSTRACTThe study of genotype × environment interaction is critical for accurate cultivar evaluation in large multi‐environment trials. Cultivars that exhibit high levels of mean performance and stability across a wide range of environmental conditions are desirable for rice production. Pure‐line varietal and hybrid rice cultivars are commercially produced in the U.S.; however, little research has been conducted comparing their stability for grain yield and milling quality. In this study, 15 hybrid and varietal cultivars were grown in 10 environments from 2005 to 2007 to determine the performance and stability of rough rice yield, whole milled rice percentages, and whole‐grain rice yield. Stability was analyzed using the coefficient of variation, Shukla's Stability Variance statistic with environment means as a covariate, and the Cultivar Superiority Measure. The hybrid rice cultivars XP723 and CLXL730 were ideal for high and stable rough rice and whole‐grain rice yields on the basis of the cultivar superiority measure; however, for whole milled rice percentage alone, they were among the least desirable cultivars. Among the varietal cultivars, Catahoula and Jupiter were ideal cultivar selections for high and stable whole‐grain rice yields. The results of this study indicate that the stability and performance of hybrid and varietal cultivars differ according to the trait of interest.
Maize Kernel Oil and Episodes of Shading during the Grain‐Filling Period
Authors: Tanaka Walter , Maddonni Gustavo Ángel 
Published: October 2009

ABSTRACTPrevious studies documented the stability of maize (Zea mays L.) kernel oil concentration for a wide range of kernel weights promoted by contrasting post‐flowering assimilate availabilities per kernel (i.e., source–sink ratios). These studies mainly modified the sink size with a low impact on the source size. In this study, we focused on kernel oil concentration response to source–sink ratio alterations promoted by different timings and intensities of shading during the effective grain‐filling period. Two crosses with contrasting kernel oil concentration (‘DK752’ × DK752 and DK752 × ‘5MG’) were tested. Kernel oil concentration was positively related to the embryo–kernel ratio (r = 0.96, P < 0.001) and embryo oil concentration (r = 0.94, P < 0.001) and crosses differed in both traits. Severe shading (85% reduction of incident solar radiation) at early stages of kernel growth reduced the final embryo–kernel ratio and the embryo oil concentration of both crosses. Contrarily, moderate shading (45% reduction of incident solar radiation) did not modify the kernel oil determinants. Kernel oil concentration and kernel weight declined when severe shading shortened the kernel growth period. Our results collectively sustain the hypothesis that maize kernel oil concentration is commonly sink‐limited. We established that kernel oil concentration of both crosses was reduced when post‐flowering plant growth rate per kernel was less than 50% of kernel growth rate.
Genetically Engineered Flax: Potential Benefits, Risks, Regulations, and Mitigation of Transgene Movement
Authors: Jhala Amit J. , Weselake Randall J. , Hall Linda M. 
Published: October 2009

ABSTRACTFlax (Linum usitatissimum L.) has been grown for more than 6000 years, primarily for oil and fiber. Advances in plant biotechnology have resulted in flax cultivars with increased herbicides resistance and there is potential to produce transgenic flax with seed oil containing fatty acids with nutraceutical properties. Flax oil is a rich source of α‐linolenic acid (ALA, 18:3cisΔ9,12,15), a precursor of the very long chain polyunsaturated fatty acids (VLCPUFA), eicosapentaenoic acid (EPA, 20:5cisΔ5,8,11,14,17), and docosahexaenoic acid (DHA, 22:6cisΔ4,7,10,13,16,19). Current research on medicinal applications of ω‐3 fatty acids, especially to reduce the risk of cardiovascular diseases and cancer, suggests that genetic modification of flax may provide substantial health benefits. There are concerns, however, with the commercialization of genetically engineered (GE) flax (which includes the potential movement of transgenes by pollen and seed, and subsequent introgression with weedy and wild relatives, impact on non‐target organisms, and changes in biodiversity). A prerequisite to the unconfined cultivation of transgenic flax is an environmental risk assessment analysis. In this paper, we discuss the history and current status of genetic transformations in flax, potential benefits and consequences of GE flax, and the government regulatory framework in Canada for regulating novel flax. Finally, we discuss the best management practices to mitigate transgene movement from transgenic flax. Our intent was to evaluate biology and agronomy to predict the environmental biosafety of GE flax before commercial cultivation.
Water Deficit, Heat Tolerance, and Persistence of Summer‐Dormant Grasses in the U.S. Southern Plains
Authors: Malinowski D. P. , Kigel J. , Pinchak W. E. 
Published: October 2009

ABSTRACTSummer‐dormant cool‐season grasses are being used in the Southern Plains of the United States in place of traditional summer‐active cultivars for high‐quality winter forage. One reason for this is the ability of cultivars with summer dormancy traits to tolerate increasing annual temperature, decreasing precipitation, and repeated severe summer droughts. Research on adaptation of these grasses and mechanisms of summer dormancy has been conducted at Vernon, TX, since 2000. The experimental location is in a semiarid, subtropical climate with bimodal rainfall pattern with peaks in May and September, and prolonged summer drought. Adaptation and persistence studies involved summer‐dormant and summer‐active cultivars of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.], orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), and hardinggrass (Phalaris aquatica L.). Summer‐active types of these grasses were not adapted to this environment and could not survive the first summer after planting. Summer‐dormant types were fully adapted and persisted for at least 5 to 8 yr, depending on species. The most adapted were tall fescue, hardinggrass, and to some extent orchardgrass [subsp. hispanica (Roth) Nyman]. Detailed studies have also been conducted by the Samuel Roberts Noble Foundation at Ardmore, OK. Both research centers have breeding programs for summer‐dormant grasses.
Summer Drought Survival Strategies and Sustainability of Perennial Temperate Forage Grasses in Mediterranean Areas
Authors: Volaire F. , Norton M. R. , Lelièvre F. 
Published: October 2009

ABSTRACTPerennial grasslands provide numerous agroenvironmental benefits due to continuous soil cover. In Mediterranean areas, chronic summer drought is expected to increase as a result of climate changes. Plant adaptations that protect meristematic tissues include dehydration delay, dehydration tolerance, and summer dormancy. Summer dormancy can only be reliably tested in plants not subjected to water deficit. Under summer irrigation, complete dormancy is manifested by cessation of growth in association with full senescence of foliage and induced dehydration of leaf bases. Incomplete dormancy occurs when leaf growth is partially constrained and associated with moderate levels of foliage senescence. Summer dormancy is under hormonal control and is induced under increasing photoperiod and temperature. Recent results show that drought cannot induce summer dormancy under early‐spring short days, although a water deficit under late‐spring long days reinforces it and could enhance drought survival. Dehydration tolerance and dormancy are independent phenomena. Summer dormancy has been correlated with superior survival after severe summer droughts in many perennial grass species. This trait has potential for improving cultivars able to meet agronomic and environmental goals.
Patterns of Dormancy and Florogenesis in Herbaceous Perennial Plants: Environmental and Internal Regulation
Authors: Kamenetsky Rina 
Published: October 2009

ABSTRACTPlant evolution in climatic areas with marked seasonal changes has led to species adaptation to periods of high and low temperatures and drought and to significant changes in their morphological structure and annual developmental cycles. One characteristic of these adaptations is the state of dormancy, in which the plants do not exhibit any visible external growth. This paper reviews dormancy and florogenesis as main components of the survival strategies of perennial herbaceous plants. Summer dormancy protects plants from negative effects of water deficit and high temperatures on vegetative and reproductive organs, and forces plant species to schedule their active development in more favorable seasons. Mechanisms of summer survival vary among species and provide different modes of adaptation to harsh environments. The interrelationship between florogenesis and dormancy is most probably controlled in meristems, where the survival strategy of the plant, including vegetative growth, flowering, drought tolerance, and formation of storage organs, is determined. Mechanisms by which summer dormancy confers summer drought survival warrant further investigation for improving agronomic and environmental traits of perennial plants.
Identification and Measurement of Summer Dormancy in Temperate Perennial Grasses
Authors: Norton Mark R. , Volaire F. , Lelièvre F. , Fukai S. 
Published: October 2009

ABSTRACTThere is an apparent increase in frequency of prolonged droughts in regions with Mediterranean climates. This has rekindled interest in the summer dormancy trait for improving drought resistance of temperate perennial pasture grasses. In orchardgrass (Dactylis glomerata L.), tall fescue [Lolium arundinaceum (Schreb.) Darbysh.], and phalaris (Phalaris aquatica L.), identification of the three common drought resistance traits of vascular plants, dehydration avoidance (or delay), dehydration tolerance, and summer dormancy, is often confused. Summer dormancy, the least common of these traits, is found in cool‐season grasses from semiarid and arid Mediterranean climates and provides an enhanced level of drought resistance. It is best measured in field‐grown plants previously exposed to low winter temperatures and short photoperiods. Those perennial grasses not exhibiting summer dormancy survive drought by avoiding and/or tolerating dehydration and express this as a response to water deficit irrespective of the season. Here we review three summer water‐supply environments, full irrigation, midsummer storm, and summer drought, for their precision and repeatability in measuring dormancy. Full irrigation and midsummer storm can be recommended, but measurement of dormancy under prolonged drought caused inconsistencies.
Stress Tolerance and Persistence of Perennial Grasses: The Role of the Summer Dormancy Trait in Temperate Australia
Authors: Nie Zhongnan , Norton M. R. 
Published: October 2009

ABSTRACTThe significantly lower annual rainfall experienced in Australia over the past decade together with projections of long‐term climate change has placed increased emphasis on the use of pasture plants with superior tolerance to environmental stress, particularly drought, to ensure persistence for the grazing industries. Summer dormancy is one of the more important traits that grasses have to adapt to environments where there is little, variable, or no summer rainfall. In this article, the role that the summer dormancy trait has played in enhancing the survival of temperate perennial grasses in Australia is reviewed with special reference to orchardgrass (cocksfoot; Dactylis glomerata L.) and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. The performance of cultivars and populations with this trait is assessed in comparison to germplasm without the trait. Other major factors such as the contribution of rooting depth to stress tolerance and their possible relationship with summer dormancy are documented and evaluated. Current knowledge of the physiological basis by which summer dormancy improves survival of summer drought is also summarized.
Breeding and Use of Summer‐Dormant Grasses in Southern Australia, with Special Reference to Phalaris
Authors: Culvenor Richard A. 
Published: October 2009

ABSTRACTThe adaptation of introduced perennial grasses in southern Australia expanded with the discovery of the Mediterranean grass phalaris (Phalaris aquatica L.) as a valuable pasture species, and the introduction of Mediterranean ecotypes of orchardgrass (Dactylis glomerata L.), and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] displaying summer dormancy. In contrast, native grasses of agricultural importance appear to have little or no endogenous summer dormancy. A brief history of cultivar development from Mediterranean germplasm is presented. Recent developments include cultivars based on summer‐dormant subsp. hispanica orchardgrass and the release of Mediterranean‐type cultivars of tall fescue. Phalaris depends on a deep root system and summer dormancy for its summer survival. Cultivars based on more summer‐dormant Moroccan ecotypes have been developed for drier environments. Work to improve phalaris for hotter, summer‐dominant rainfall areas is being extended to enhance the range of perennials for the cropping zone. In addition to ecotype evaluation, breeders should employ recurrent selection in cultivars and populations such as those developed recently for low‐ to medium‐rainfall areas in orchardgrass and tall fescue.
Summer Dormancy in Australian Perennial Grasses: Historical Background, a Simulation Study, and Current Research
Authors: Clark Steve , Harris Carol 
Published: October 2009

ABSTRACTThe need for summer‐dormant, perennial, temperate grass cultivars in Australia has increased since European‐style agriculture arrived and began to push further inland into the drier pastoral zones. Early attempts to breed cultivars for marginal environments resulted in a few notable successes, but many failures resulted due to poor marketing, a lack of understanding of the environment, and economic downturns. A new spur to summer‐dormant cultivar development is climate change with predictions of lower and more erratic rainfall and higher temperatures. This paper discusses briefly the history of temperate perennial grass breeding as it relates to summer‐dormant cultivar development. Two case studies are presented. Simulations of higher input summer‐dormant grass pastures vs. unimproved annual grass pastures are examined for long‐term production and profitability under current and predicted climate scenarios. The current orchardgrass (syn. cocksfoot, Dactylis glomerata L.) and tall fescue [Lolium arundinaceum (Schreb.) Darbysh. = Schedonorus arundinaceus (Schreb.) Dumort.] breeding and commercialization programs are described.
Modeling Tiller Density, Growth, and Yield of Mediterranean Perennial Grasslands with STICS
Authors: Ruget Françoise , Satger Sylvain , Volaire Florence , Lelièvre François 
Published: October 2009

ABSTRACTA generic crop model (STICS) was adapted (STICS–Grassland) to model growth, yield, and environmental impacts of grasslands in France. It is a semimechanistic model combining equations of physiological processes and mathematical relationships between processes in a daily time step. The Information et Suivi Objectif des Prairies (ISOP; Grassland Information and Objective Survey) application was developed to estimate and map the real‐time status of grass growth and forage production in the 200 forage regions of France, to help decision makers anticipate forage availability in case of severe deficits. Initially, the model could not simulate long, severe droughts typical of Mediterranean regions when plant and tiller densities are significantly reduced. A tiller density module models the dynamics of tiller death during droughts. Since STICS is based on the concept of a mean plant (tiller) covering the whole field, variability was introduced through a γ law distribution of transpiration deficit by tiller, a threshold value imposing desiccation, and death to tillers reaching this level. Its second part generates incomplete or total recovery of tiller density through new tillering in the next wet season. Species and contrasting groups of cultivars within species can be characterized with a limited number of parameters.
Current and Potential Development of Perennial Grasses in Rainfed Mediterranean Farming Systems
Authors: Lelièvre François , Volaire Florence 
Published: October 2009

ABSTRACTPast and recent development of perennial grasses in the rainfed Euro‐Mediterranean region is reviewed concerning climatic constraints and main types of farming systems. The few Mediterranean cultivars that are registered and available are used for livestock production and cover crops only in subtemperate areas. These cultivars are adapted where annual rainfall exceeds 500 mm and accumulated water deficit from May to September is <800 mm. For the future, grass–legume mixtures need to be developed to meet the contrasting situations of livestock production and environmental use, with both functions contributing to farm income through the market and from public subsidies. Concern for environmental uses of perennial grasses raises interest in new germplasm that could accelerate cultivar breeding and seed production. Research programs should ensure a diversification of available germplasm in the principal forage species for phenology, drought tolerance, summer dormancy levels, and dehydration tolerance.
Summer Dormancy in Orchardgrass: Evaluation and Characterization through Ecophysiological and Genetic Studies
Authors: Shaimi Naima , Kallida Rajae , Volaire Florence , Faiz Chaouki Al 
Published: October 2009

ABSTRACTClimatic change manifested by increasing summer drought necessitates the development of drought‐tolerant forage grass cultivars. Summer dormancy is a major trait conferring drought survival and autumn recovery of perennial grasses in Mediterranean areas. Moroccan ecotypes of orchardgrass (Dactylis glomerata L.) expressed 67% greater degree of summer dormancy than tested cultivars except the highly dormant ‘Kasbah.’ Furthermore, summer dormancy was highly correlated with perenniality (r = 0.63, P < 0.01). However, summer dormancy was associated with low productivity. A breeding program was started to develop productive orchardgrass cultivars with high summer dormancy. Hybrids between high‐ and low‐dormancy cultivars produced offspring with combinations of enhanced dormancy and biomass production indicating potential for breaking the negative dormancy‐yield association. For example, Kasbah (dormant) × ‘Medly’ (summer‐active) hybrids were 57% more dormant than Medly and 32% higher yielding than Kasbah. Genetic analysis of heritability and molecular markers will provide more information on the genetic control of summer dormancy. Results of crosses between contrasting populations of orchardgrass indicate potential for combining the desirable traits of summer dormancy and high annual herbage yield into an eventual cultivar.
Breeding Summer‐Dormant Grasses for the United States
Authors: Hopkins A. A. , Bhamidimarri S. 
Published: October 2009

ABSTRACTSummer dormancy can lead to increased drought tolerance and persistence in cool‐season grasses. Here we describe efforts to develop summer‐dormant cultivars in the United States. Summer‐dormant grasses are generally well adapted to the Southern Plains but have poor persistence as well as low productivity east and north of this region because of limited winter hardiness and other factors. This limited geographic adaptation is thought to be due to germplasm background rather than the summer dormancy trait. Depending on the target environment, improved cultivars could be developed by selecting within existing summer‐dormant material or by crossing the trait into adaptive germplasm. Difficulties in phenotyping summer dormancy, and in some instances fertility barriers across germplasm sources, will need to be overcome to utilize the latter approach.
Fitting Germplasm Types of Tall Fescue and Orchardgrass to Different Cropping Environments of the Mediterranean Region
Authors: Pecetti L. , Annicchiarico P. , Porqueddu C. , Khedim A. , Abdelguerfi A. 
Published: October 2009

ABSTRACTUnderstanding of adaptation targets, selection environments, genetic resources, and plant types is required in breeding tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbysh.] and orchardgrass (Dactylis glomerata L.) for Mediterranean environments prone to drought stress. Fourth‐year forage yield of seven orchardgrass and five fescue cultivars grown in Algeria and Sardinia revealed (i) crossover cultivar × location interaction in orchardgrass, with dormant germplasm performing best in the drier Algerian site, and nondormant Mediterranean material performing best in Sardinia; and (ii) the advantage of tall fescue over orchardgrass in both sites. Yield of Algerian populations of orchardgrass and tall fescue grown in Algeria was generally lower than the best control (‘Flecha’ tall fescue). Other studies in Italy showed (i) the possibility to select orchardgrass from Mediterranean germplasm that combines summer survival under moderate stress with response to summer rain events; (ii) the nil effect in a Mediterranean site, and the slightly positive effect in a subcontinental climate site of endophyte infection on tall fescue survival; and (iii) the adaptation of Mediterranean and Continental fescue germplasm to their respective climatic areas.