The Experts below are selected from a list of 1926 Experts worldwide ranked by ideXlab platform
R P Ellis - One of the best experts on this subject based on the ideXlab platform.
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detection of quantitative trait loci for agronomic yield grain and disease characters in spring barley hordeum vulgare l
Theoretical and Applied Genetics, 1995Co-Authors: W T B Thomas, W Powell, R Waugh, K J Chalmers, U M Barua, P Jack, V Lea, B P Forster, J S Swanston, R P EllisAbstract:Quantitative trait loci (QTLs) have been revealed for characters in a segregating population from a spring barley cross between genotypes adapted to North-West Europe. Transgressive Segregation was found for all the characters, which was confirmed by the regular detection of positive and negative QTLs from both parents. A QTL for all the agronomic, yield and grain characters measured except thousand grain weight was found in the region of the denso dwarfing gene locus. There were considerable differences between the location of QTLs found in the present study and those found in previous studies of North American germ plasm, revealing the diversity between the two gene pools. Thirty-one QTLs were detected in more than one environment for the 13 characters studied, although many more were detected in just one environment. Whilst biometrical analyses suggested the presence of epistasis in the genetic control of some characters, there was little evidence of interactions between the QTLs apart from those associated with yield. QTLs of large effect sometimes masked the presence of QTLs of smaller effect.
W Powell - One of the best experts on this subject based on the ideXlab platform.
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understanding the classics the unifying concepts of Transgressive Segregation inbreeding depression and heterosis and their central relevance for crop breeding
Plant Biotechnology Journal, 2021Co-Authors: Ian Mackay, James Cockram, Phil Howell, W PowellAbstract:Transgressive Segregation and heterosis are the reasons that plant breeding works. Molecular explanations for both phenomena have been suggested and play a contributing role. However, it is often overlooked by molecular genetic researchers that Transgressive Segregation and heterosis are most simply explained by dispersion of favorable alleles. Therefore, advances in molecular biology will deliver the most impact on plant breeding when integrated with sources of heritable trait variation - and this will be best achieved within a quantitative genetics framework. An example of the power of quantitative approaches is the implementation of genomic selection, which has recently revolutionized animal breeding. Genomic selection is now being applied to both hybrid and inbred crops and is likely to be the major source of improvement in plant breeding practice over the next decade. Breeders' ability to efficiently apply genomic selection methodologies is due to recent technology advances in genotyping and sequencing. Furthermore, targeted integration of additional molecular data (such as gene expression, gene copy number and methylation status) into genomic prediction models may increase their performance. In this review, we discuss and contextualize a suite of established quantitative genetics themes relating to hybrid vigour, Transgressive Segregation and their central relevance to plant breeding, with the aim of informing crop researchers outside of the quantitative genetics discipline of their relevance and importance to crop improvement. Better understanding between molecular and quantitative disciplines will increase the potential for further improvements in plant breeding methodologies and so help underpin future food security.
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detection of quantitative trait loci for agronomic yield grain and disease characters in spring barley hordeum vulgare l
Theoretical and Applied Genetics, 1995Co-Authors: W T B Thomas, W Powell, R Waugh, K J Chalmers, U M Barua, P Jack, V Lea, B P Forster, J S Swanston, R P EllisAbstract:Quantitative trait loci (QTLs) have been revealed for characters in a segregating population from a spring barley cross between genotypes adapted to North-West Europe. Transgressive Segregation was found for all the characters, which was confirmed by the regular detection of positive and negative QTLs from both parents. A QTL for all the agronomic, yield and grain characters measured except thousand grain weight was found in the region of the denso dwarfing gene locus. There were considerable differences between the location of QTLs found in the present study and those found in previous studies of North American germ plasm, revealing the diversity between the two gene pools. Thirty-one QTLs were detected in more than one environment for the 13 characters studied, although many more were detected in just one environment. Whilst biometrical analyses suggested the presence of epistasis in the genetic control of some characters, there was little evidence of interactions between the QTLs apart from those associated with yield. QTLs of large effect sometimes masked the presence of QTLs of smaller effect.
Loren H Rieseberg - One of the best experts on this subject based on the ideXlab platform.
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the role of homoploid hybridization in evolution a century of studies synthesizing genetics and ecology
American Journal of Botany, 2014Co-Authors: Sarah B Yakimowski, Loren H RiesebergAbstract:While homoploid hybridization was viewed as maladaptive by zoologists, the possibility that it might play a creative role in evolution was explored and debated by botanists during the evolutionary synthesis. Owing to his synthetic work on the ecological and genetic factors influencing the occurrence and effects of hybridization, G. Ledyard Stebbins' contributions to this debate were particularly influential. We revisit Stebbins' views on the frequency of hybridization, the evolution of hybrid sterility, and the evolutionary importance of Transgressive Segregation, introgression, and homoploid hybrid speciation in the context of contemporary evidence. Floristic surveys indicate that ∼10% of plant species hybridize, suggesting that natural hybridization is not as ubiquitous as Stebbins argued. There is stronger support for his contention that chromosomal sterility is of greater importance in plants than in animals and that selection drives the evolution of hybrid sterility. Stebbins' assertions concerning the frequent occurrence of Transgressive Segregation and introgressive hybridization have been confirmed by contemporary work, but few studies directly link these phenomena to adaptive evolution or speciation. Stebbins proposed a mechanism by which chromosomal rearrangements partially isolate hybrid lineages and parental species, which spurred the development of the recombinational model of homoploid speciation. While this model has been confirmed empirically, the establishment of reproductively independent hybrid lineages is typically associated with the development of both intrinsic and extrinsic reproductive barriers. We conclude by reflecting on outcomes of hybridization not considered by Stebbins and on possible future research that may extend our understanding of the evolutionary role of hybridization beyond Stebbins' legacy.
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the origin of ecological divergence in helianthus paradoxus asteraceae selection on Transgressive characters in a novel hybrid habitat
Evolution, 2003Co-Authors: Christian Lexer, Mark E. Welch, Olivier Raymond, Loren H RiesebergAbstract:Diploid hybrid speciation in plants is often accompanied by rapid ecological divergence between incipient neospecies and their parental taxa. One plausible means by which novel adaptation in hybrid lineages may arise is Transgressive Segregation, that is, the generation of extreme phenotypes that exceed those of the parental lines. Early generation (BC2) hybrids between two wild, annual sunflowers, Helianthus annuus and Helianthus petiolaris, were used to study directional selection on Transgressive characters associated with the origin of Helianthus paradoxus, a diploid hybrid species adapted to extremely saline marshes. The BC2 plants descended from a single F1 hybrid backcrossed toward H. petiolaris. The strength of selection on candidate adaptive traits in the interspecific BC2 was measured in natural H. paradoxus salt marsh habitat. Positive directional selection was detected for leaf succulence and Ca uptake, two traits that are known to be important in salt stress response in plants. Strong negative directional selection operated on uptake of Na and correlated elements. A significant decrease in trait correlations over time was observed in the BC2 population for Na and Ca content, suggesting an adaptive role for increased Ca uptake coupled with increased net exclusion of Na from leaves. Patterns of directional selection in BC2 hybrids were concordant with character expression in the natural hybrid species, H. paradoxus, transplanted into the wild. Moreover, the necessary variation for generating the H. paradoxus phenotype existed only in the BC2 population, but not in samples of the two parental species, H. annuus and H. petiolaris. These results are consistent with the hypothesis that Transgressive Segregation of elemental uptake and leaf succulence contributed to the origin of salt adaptation in the diploid hybrid species H. paradoxus.
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the genetic architecture necessary for Transgressive Segregation is common in both natural and domesticated populations
Philosophical Transactions of the Royal Society B, 2003Co-Authors: Loren H Rieseberg, Alex Widmer, Michele A Arntz, John M BurkeAbstract:Segregating hybrids often exhibit phenotypes that are extreme or novel relative to the parental lines. This phenomenon is referred to as Transgressive Segregation, and it provides a mechanism by which hybridization might contribute to adaptive evolution. Genetic studies indicate that Transgressive Segregation typically results from recombination between parental taxa that possess quantitative trait loci (QTLs) with antagonistic effects (i.e. QTLs with effects that are in the opposite direction to parental differences for those traits). To assess whether this genetic architecture is common, we tabulated the direction of allelic effects for 3252 QTLs from 749 traits and 96 studies. Most traits (63.6%) had at least one antagonistic QTL, indicating that the genetic substrate for Transgressive Segregation is common. Plants had significantly more antagonistic QTLs than animals, which agrees with previous reports that Transgressive Segregation is more common in plants than in animals. Likewise, antagonistic QTLs were more frequent in intra- than in interspecific crosses and in morphological than in physiological traits. These results indicate that Transgressive Segregation provides a general mechanism for the production of extreme phenotypes at both above and below the species level and testify to the possible creative part of hybridization in adaptive evolution and speciation.
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Transgressive Segregation, adaptation and speciation
Heredity, 1999Co-Authors: Loren H Rieseberg, Margaret A Archer, Robert K WayneAbstract:The production of extreme or ‘Transgressive’ phenotypes in segregating hybrid populations has been speculated to contribute to niche divergence of hybrid lineages. Here, we assess the frequency of Transgressive Segregation in hybrid populations, describe its genetic basis and discuss the factors that best predict its occurrence. From a survey of 171 studies that report phenotypic variation in segregating hybrid populations, we show that transgression is the rule rather than the exception. In fact, 155 of the 171 studies (91%) report at least one Transgressive trait, and 44% of 1229 traits examined were Transgressive. Transgression occurred most frequently in intraspecific crosses involving inbred, domesticated plant populations, and least frequently in interspecific crosses between outbred, wild animal species. Quantitative genetic studies of plant hybrids consistently point to the action of complementary genes as the primary cause of transgression, although overdominance and epistasis also contribute. Complementary genes appear to be common for most traits, with the possible exception of those with a history of disruptive selection. These results lend credence to the view that hybridization may provide the raw material for rapid adaptation and provide a simple explanation for niche divergence and phenotypic novelty often associated with hybrid lineages.
Eric B Holub - One of the best experts on this subject based on the ideXlab platform.
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Transgressive Segregation reveals mechanisms of Arabidopsis immunity to Brassica-infecting races of white rust (Albugo candida)
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Volkan Cevik, Freddy Boutrot, Wiebke Apel, Alexandre Robert-seilaniantz, Oliver J Furzer, Amey Redkar, Baptiste Castel, Paula X Kover, David C Prince, Eric B HolubAbstract:Arabidopsis thaliana accessions are universally resistant at the adult leaf stage to white rust (Albugo candida) races that infect the crop species Brassica juncea and Brassica oleracea. We used Transgressive Segregation in recombinant inbred lines to test if this apparent species-wide (nonhost) resistance in A. thaliana is due to natural pyramiding of multiple Resistance (R) genes. We screened 593 inbred lines from an Arabidopsis multiparent advanced generation intercross (MAGIC) mapping population, derived from 19 resistant parental accessions, and identified two Transgressive segregants that are susceptible to the pathogen. These were crossed to each MAGIC parent, and analysis of resulting F2 progeny followed by positional cloning showed that resistance to an isolate of A. candida race 2 (Ac2V) can be explained in each accession by at least one of four genes encoding nucleotide-binding, leucine-rich repeat (NLR) immune receptors. An additional gene was identified that confers resistance to an isolate of A. candida race 9 (AcBoT) that infects B. oleracea. Thus, effector-triggered immunity conferred by distinct NLR-encoding genes in multiple A. thaliana accessions provides species-wide resistance to these crop pathogen
Atsushi Yoshimura - One of the best experts on this subject based on the ideXlab platform.
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qtl detection for eating quality of cooked rice in a population of chromosome segment substitution lines
Theoretical and Applied Genetics, 2004Co-Authors: Xiangyuan Wan, Hideshi Yasui, J M Wan, Changbiao Wang, W B Shen, Haihai Wang, Ling Jiang, Shijia Liu, Liangming Chen, Atsushi YoshimuraAbstract:The genetic mechanism underlying six palatability properties of cooked rice and three physico-chemical traits was dissected in 66 BC3F2 chromosome segment substitution lines (CSSLs), using a complete linkage map in three successive years. The CSSLs showed Transgressive Segregation for all traits studied. Significant correlation was detected among most palatability traits. A total of 25 QTLs for the nine traits were identified on nine chromosomes, and many QTLs affecting different quality traits were mapped in the same regions. Six QTLs—qLT-8 for luster, qTD-6 and qTD-8 for tenderness, qIVOE-6 and qIVOE-8 for integrated value of organoleptic evaluation, and qAC-8 for amylose content—were repeatedly detected across the 3 years. Phenotypic values were significantly different between the recurrent parent, cultivar Asominori, and the CSSLs harboring any of the six QTL alleles across the three environments, indicating that these six QTLs were non-environment-specific and could be used for marker-assisted selection in rice quality improvement.
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quantitative trait locus mapping of ovicidal response in rice oryza sativa l against whitebacked planthopper sogatella furcifera horvath
Crop Science, 1999Co-Authors: Masanori Yamasaki, Hiroshi Tsunematsu, Atsushi Yoshimura, Nobuo Iwata, Hideshi YasuiAbstract:The ovicidal response in rice (Oryza sativa L.) to whitebacked planthopper (WBPH), Sogatella furcifera Horvath, is characterized by the formation of watery lesions which result in the death of WBPH eggs. To determine the genetic mechanism of this ovicidal response, a set of 71 rice recombinant inbred (RI) lines (F 8 , F 9 , and F 10 ) derived from a cross of japonica cultivar Asominori and indica cultivar IR24, the two parents, and the F 1 were phenotyped for percentage of watery lesions (PWL) and WBPH egg mortality (EM). PWL and EM showed significant positive correlations (P < 0.001) and Transgressive Segregation was observed for both traits. A total of 10 quantitative trait loci (QTLs) for ovicidal response were detected with 292 RFLP markers in the F 6 and F 7 populations by composite interval mapping (LOD ≥ 1.5). Four of 10 QTLs coincided for PWL and EM and each three QTLs were only detected for PWL and EM. The QTL on chromosome 6 (R1954-L688) was most significantly associated with the ovicidal response and accounted for 69.9% of phenotypic variance for PWL (F 8 ) and 46.0% of phenotypic variance for EM (F 8 ). Positive alleles for ovicidal response came from Asominori on chromosomes 1, 3, 6S (short arm), 8, and 12 and from IR24 on chromosomes 2, 6L (long arm), and 10. QTL accumulation from both parents was the genetic basis of the Transgressive Segregation in the RI population. No epistatic interaction was detected. The Asominori allele on the chromosome 6S QTL was essential to the ovicidal response, and R1954 was found to be a target marker for marker assisted selection.
