No description available.

The main drivers of microevolution in the genus Sorbus are interspecific hybridisation and polyploidy. The fate of new hybrid and polyploid taxa is determined by their mode of reproduction. Especially apomixis could be very advantageous for these new taxa. The S. aria agg. (subg. Aria) plays an important role within the genus since its members are involved in all hybridisation events and thereby is responsible for the substantial part of variation of the genus. Flow cytometry, molecular markers and multivariate morphological analyses were employed to evaluate the processes generating the variability in the S. aria group. Three ploidy levels were detected among species from subg. Aria in the Czech Republic. All of them could be found in the South Moravia, whereas only tetraploids occur in the Bohemia region. Moreover, most of the Czech taxa (5 out of 7) grow also only in the South Moravia which is therefore considered as a centre of diversity of the genus Sorbus in the Czech Republic. Flow cytometry seed screen revealed 7 modes of reproduction among the individuals from S. aria agg. A wide range of sexual and apomictic types of reproduction including reduced and unreduced gametes was detected. All of the diploid individuals are completely sexual. Among polyploid taxa, most of the species are...

The resistance of Palmer amaranth (PA) and the tolerance (natural resistance) of pitted morningglory (PM) to glyphosate have made these species among the most common and troublesome weeds in the southeastern U.S. since the adoption of glyphosate-resistant (GR) crops. Populations of GR PA (R1 and R2) were identified in Mississippi. The inheritance of glyphosate resistance was examined in reciprocal crosses (RC) between glyphosate-resistant (R) and -susceptible (S) parents (Female-S × Male-R, S/R, and Female-R × Male-S, R/S), and second reciprocal crosses (2RC) (Female-S/R × Male-S/R, S/R//S/R, and Female-R/S × Male-R/S, R/S//R/S). Dose-response assays resulted in 17- to 4old resistance to glyphosate compared with S. Population S accumulated 325- and 8-times more shikimate at the highest glyphosate dose than in R1 and R2, respectively. cDNA sequence analysis of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene indicated no target site mutation. Genomes of R1, R2, RC, and 2RC contained from 1- to 59old more copies of EPSPS gene than S; EPSPS was highly expressed in R1 and R/S, but was poorly expressed in S, S/R, and R2. EPSPS activity was lower in S and S/R than in R and R/S, glyphosate absent; all were inhibited by glyphosate. Western Blot analysis confirmed an increased EPSPS protein level to EPSPS copy number correlation. Thus, the level of resistance was decidedly influenced by the direction of the cross. R and S female plants were reproductively isolated and seed were still produced, suggesting that PA can produce seed both apomictically and sexually (facultative apomixis). This mode of reproduction determined the low copy number inheritance, as well as guaranteeing the GR trait stability in the R populations. Dose-response assays resulted in 2.6old variability in tolerance to glyphosate between the most tolerant (MT) and the least tolerant (LT) PM populations. The level of tolerance positively correlated with the time of exposure to GR-crop system. Less shikimate was recovered in MT as compared to LT. Levels of aminomethylphosphonic acid (AMPA) were not different between populations and sarcosine was not present in either populations. Consequently, metabolism of glyphosate to AMPA or sarcosine is not a common factor in explaining natural resistance levels.

No description available.

Apomixis, or asexual seed development, if introduced into crop species, has the potential to greatly improve global food production. Towards this goal, this study focused on uncovering the genetic mechanisms that control the parthenogenesis step within apomixis whereby fertilisation is avoided. In the model apomict, Hieracium praealtum (Asteraceae), parthenogenesis is controlled by the LOSS OF PARTHENOGENESIS (LOP) locus. Previous research showed that in addition to genomic copies of candidate genes at LOP, the genome has at least three other copies referred to as alternative alleles. The main goal of this study was to investigate four candidate genes, Genes B, X, H and Y, at LOP by generating segregation data of the alternative alleles. BAC clones containing alternative allele sequences were identified and Roche 454 pyrosequenced. These sequences were used to design alternative allele specific primers for genotyping two Hieracium praealtum polyhaploid populations (~ 300 plants). Four major conclusions were drawn from this study. First, the alternative alleles were in fact acting like alleles to the LOP alleles of Genes B, X and Y. Second, allelic sequence divergence (ASD) of the LOP alleles of Genes B and X relative to the alternative alleles, indicated a recent and separate evolutionary history. Third and, unexpectedly, recombination was detected at the LOP locus, in contrast to other apomixis loci reported in the literature. Furthermore, Gene B was found to be very closely associated with parthenogenesis in the polyhaploid population indicating that it may be essential to parthenogenesis and therefore requires further investigation. On the other hand, the absence of Genes X, Y and H, due to recombination, had no impact upon parthenogenesis. Fourth, the sequence data suggested that the LOP and alternative alleles originated from a shared common allele ancestor. It is hoped that these findings have made a significant contribution towards the future goal of introducing apomixis into crop species.

A riqueza e a diversidade de espécies forrageiras dos Campos Sulinos, pode propiciar a inserção de espécies nativas em programas de melhoramento. As gramíneas nativas do gênero Paspalum possuem grande variabilidade, que pode contribuir para seleção de genótipos adaptáveis às várias condições ecológicas de regiões tropicais e subtropicais. Dentre as espécies deste gênero destaca-se o Paspalum notatum com ecótipos que possuem superioridade produtiva quando comparados à cultivares comerciais, o que contribui para que esta espécie seja candidata ao lançamento de novas cultivares. Avaliações de plantas melhoradas submetidas a diferentes práticas de manejo, como fertilização ou consorciação, são fundamentais para gerar conhecimento acerca das características produtivas. O objetivo deste trabalho foi avaliar o potencial produtivo de uma progênie híbrida intraespecífica de P. notatum submetida a diferentes níveis de fertilização nitrogenada ou consorciação com leguminosas para serem empregados em sistemas de produção a pasto ou na recuperação de pastagens naturais degradadas. A produção de matéria seca e a densidade populacional de perfilhos dos genótipos de P. notatum respondem de forma positiva aos níveis de fertilização nitrogenada. O nível de fertilização 120 kg N ha-1ano-1 promove a maior eficiência de uso de nitrogênio nos genótipos de P. notatum. Os genótipos B26, C22, C9 e Bagual são indicados para serem utilizados em sistemas de consórcio com leguminosas de clima temperado. A produção de matéria seca de sistemas com genótipos de P. notatum consorciados com trevo branco mais cornichão é semelhante à produção de sistemas fertilizados com até 240 kg N ha-1ano-1, evidenciando a viabilidade do consórcio entre essas espécies. / The richness and diversity of forage species in the Campos Sulinos region may facilitate the inclusion of native species in breeding programs. Native grasses of the Paspalum genus show great variability which may contribute to the selection of adaptable genotypes to the various ecological conditions of tropical and subtropical regions. Within the genus, Paspalum notatum is a species with superiorly productive ecotypes compared to commercial cultivars, rendering this species a candidate for the release of new cultivars. The evaluation of bred plants submitted to different management practices, such as fertilization or consortium with legumes is fundamental to acquire knowledge about the productive features. The objective of the present work was to evaluate the productive potential of an intraspecific hybrid progeny of Paspalum notatum submitted to different nitrogen fertilization levels or intercropped with legumes, with the objective of being used in grazing systems or in the recovery of degraded natural pastures. The dry matter yield and tiller population density of Paspalum notatum genotypes respond positively to nitrogen fertilization levels. The 120 kg N ha-1year-1 fertilization level promotes the highest nitrogen utilization efficiency in Paspalum notatum. Genotypes B26, C22, C9 and Bagual are indicated for legume intercropped systems with temperate legumes. The dry matter production of intercropped systems between Paspalum notatum genotypes with white clover plus birdsfoot trefoil is similar to the production of systems fertilized with up to 240 kg N ha-1year-1, demonstrating the viability of the intercropped between these species.

A riqueza e a diversidade de espécies forrageiras dos Campos Sulinos, pode propiciar a inserção de espécies nativas em programas de melhoramento. As gramíneas nativas do gênero Paspalum possuem grande variabilidade, que pode contribuir para seleção de genótipos adaptáveis às várias condições ecológicas de regiões tropicais e subtropicais. Dentre as espécies deste gênero destaca-se o Paspalum notatum com ecótipos que possuem superioridade produtiva quando comparados à cultivares comerciais, o que contribui para que esta espécie seja candidata ao lançamento de novas cultivares. Avaliações de plantas melhoradas submetidas a diferentes práticas de manejo, como fertilização ou consorciação, são fundamentais para gerar conhecimento acerca das características produtivas. O objetivo deste trabalho foi avaliar o potencial produtivo de uma progênie híbrida intraespecífica de P. notatum submetida a diferentes níveis de fertilização nitrogenada ou consorciação com leguminosas para serem empregados em sistemas de produção a pasto ou na recuperação de pastagens naturais degradadas. A produção de matéria seca e a densidade populacional de perfilhos dos genótipos de P. notatum respondem de forma positiva aos níveis de fertilização nitrogenada. O nível de fertilização 120 kg N ha-1ano-1 promove a maior eficiência de uso de nitrogênio nos genótipos de P. notatum. Os genótipos B26, C22, C9 e Bagual são indicados para serem utilizados em sistemas de consórcio com leguminosas de clima temperado. A produção de matéria seca de sistemas com genótipos de P. notatum consorciados com trevo branco mais cornichão é semelhante à produção de sistemas fertilizados com até 240 kg N ha-1ano-1, evidenciando a viabilidade do consórcio entre essas espécies. / The richness and diversity of forage species in the Campos Sulinos region may facilitate the inclusion of native species in breeding programs. Native grasses of the Paspalum genus show great variability which may contribute to the selection of adaptable genotypes to the various ecological conditions of tropical and subtropical regions. Within the genus, Paspalum notatum is a species with superiorly productive ecotypes compared to commercial cultivars, rendering this species a candidate for the release of new cultivars. The evaluation of bred plants submitted to different management practices, such as fertilization or consortium with legumes is fundamental to acquire knowledge about the productive features. The objective of the present work was to evaluate the productive potential of an intraspecific hybrid progeny of Paspalum notatum submitted to different nitrogen fertilization levels or intercropped with legumes, with the objective of being used in grazing systems or in the recovery of degraded natural pastures. The dry matter yield and tiller population density of Paspalum notatum genotypes respond positively to nitrogen fertilization levels. The 120 kg N ha-1year-1 fertilization level promotes the highest nitrogen utilization efficiency in Paspalum notatum. Genotypes B26, C22, C9 and Bagual are indicated for legume intercropped systems with temperate legumes. The dry matter production of intercropped systems between Paspalum notatum genotypes with white clover plus birdsfoot trefoil is similar to the production of systems fertilized with up to 240 kg N ha-1year-1, demonstrating the viability of the intercropped between these species.

A riqueza e a diversidade de espécies forrageiras dos Campos Sulinos, pode propiciar a inserção de espécies nativas em programas de melhoramento. As gramíneas nativas do gênero Paspalum possuem grande variabilidade, que pode contribuir para seleção de genótipos adaptáveis às várias condições ecológicas de regiões tropicais e subtropicais. Dentre as espécies deste gênero destaca-se o Paspalum notatum com ecótipos que possuem superioridade produtiva quando comparados à cultivares comerciais, o que contribui para que esta espécie seja candidata ao lançamento de novas cultivares. Avaliações de plantas melhoradas submetidas a diferentes práticas de manejo, como fertilização ou consorciação, são fundamentais para gerar conhecimento acerca das características produtivas. O objetivo deste trabalho foi avaliar o potencial produtivo de uma progênie híbrida intraespecífica de P. notatum submetida a diferentes níveis de fertilização nitrogenada ou consorciação com leguminosas para serem empregados em sistemas de produção a pasto ou na recuperação de pastagens naturais degradadas. A produção de matéria seca e a densidade populacional de perfilhos dos genótipos de P. notatum respondem de forma positiva aos níveis de fertilização nitrogenada. O nível de fertilização 120 kg N ha-1ano-1 promove a maior eficiência de uso de nitrogênio nos genótipos de P. notatum. Os genótipos B26, C22, C9 e Bagual são indicados para serem utilizados em sistemas de consórcio com leguminosas de clima temperado. A produção de matéria seca de sistemas com genótipos de P. notatum consorciados com trevo branco mais cornichão é semelhante à produção de sistemas fertilizados com até 240 kg N ha-1ano-1, evidenciando a viabilidade do consórcio entre essas espécies. / The richness and diversity of forage species in the Campos Sulinos region may facilitate the inclusion of native species in breeding programs. Native grasses of the Paspalum genus show great variability which may contribute to the selection of adaptable genotypes to the various ecological conditions of tropical and subtropical regions. Within the genus, Paspalum notatum is a species with superiorly productive ecotypes compared to commercial cultivars, rendering this species a candidate for the release of new cultivars. The evaluation of bred plants submitted to different management practices, such as fertilization or consortium with legumes is fundamental to acquire knowledge about the productive features. The objective of the present work was to evaluate the productive potential of an intraspecific hybrid progeny of Paspalum notatum submitted to different nitrogen fertilization levels or intercropped with legumes, with the objective of being used in grazing systems or in the recovery of degraded natural pastures. The dry matter yield and tiller population density of Paspalum notatum genotypes respond positively to nitrogen fertilization levels. The 120 kg N ha-1year-1 fertilization level promotes the highest nitrogen utilization efficiency in Paspalum notatum. Genotypes B26, C22, C9 and Bagual are indicated for legume intercropped systems with temperate legumes. The dry matter production of intercropped systems between Paspalum notatum genotypes with white clover plus birdsfoot trefoil is similar to the production of systems fertilized with up to 240 kg N ha-1year-1, demonstrating the viability of the intercropped between these species.

Apomixis (asexual reproduction by seeds) has the considerable potential in agriculture and crop breeding due to its ability to produce genetically identical progenies in a form of persistent propagules, i.e. seeds. However, the processes laying behind the origin of apomixis and connected molecular mechanisms are still unknown. Despite the fact, that apomicts are considered to be an evolutionary dead-ends, they are often more widely distributed than their sexual relatives (this phenomenon is commonly referred to as geographical parthenogenesis (GP). Although this phenomenon is studied for decades, its causes are still not fully understood. Importantly, several recent studies pointed out that apomicts with limited genetic variability can at some extent react to changing environment through changes in gene transcription by epigenetic modifications. It is generally assumed, that hybridisation and polyploidization played a crucial role in the emergence of apomixis. For this reason, presented studies test the putative origin of selected polyploid apomicts and if the interspecific hybridisation between diploid sexuals triggers polyploidization using predominantly polyploid and apomictic genus Hieracium s. str. Surprisingly, the presented study demonstrates the hybrid origin of almost all investigated...

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 112-121). Also available on the World Wide Web.