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Do Severe Genetic Bottlenecks Lead to Greater Reproductive Failure?Burrows, Ben Robert January 2006 (has links)
It is generally accepted that populations which experience severe bottlenecks have a reduction in fitness. One of the most frequently reported fitness costs is increased hatching failure in bottlenecked populations of birds. The mechanism responsible for increased hatching failure is unknown. Research on other animals suggest that reduced population numbers cause unavoidable inbreeding that in turn leads to abnormalities in the gametes. In this thesis I examine some of the possible causes for increased hatching failure in severely bottlenecked populations of introduced birds in New Zealand. I look at three traits identified as a cause for infertility or hatching failure previously and determine whether there is a link with the size of a population s bottleneck. It is possible that reduced numbers of sperm reaching the site of fertilisation is a primary cause of hatching failure. I examined the perivitelline membrane of various species of introduced birds and counted the total number of sperm present to compare to how many would be expected in non-bottlenecked species. Although there was no relationship between the size of the bottleneck and the number of sperm present, all species had lower than expected sperm counts. In many species of mammals, a reduction in the quality of sperm is attributed to inbreeding depression bought about by genetic bottlenecks. I next compared the level of sperm abnormalities, variation in midpiece size sperm, and sperm motility with the size of the bottleneck each species passed through when introduced to New Zealand. There was no significant correlation between either the variation in midpiece size or sperm motility with bottleneck size. However, there was a trend for species that passed through more severe bottlenecks to have a slightly higher level of midpiece size and lower motility. Finally, I examined whether there was a link between abnormalities in the eggshell and the size of the respective bottleneck. There was no significant change in eggshell thickness or any change in the number of pores associated bottleneck size. However, there was a decreased number of round pores in severely bottlenecked species, although the consequences of this are unknown. My findings do not directly link a single cause for increased hatching failure in bottlenecked species of birds, but they do highlight the need for monitoring of reproductive traits in endangered species that have experienced a population bottleneck.
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Endogamia em rebanhos de caprinos da raça Saanen / Inbreeding in herds of Saanen breed goatsPaiva, Renato Diógenes Macedo 25 February 2016 (has links)
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Previous issue date: 2016-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Saanen goat breed is present in all countries that have a fairly developed dairy goat and the predominant race in farms and with higher milk production average. The objective of this study was to evaluate the population structure and the effect of inbreeding on the production of milk up to 305 days of lactation and duration of lactation in Saanen goats belonging to participating flocks of Breeding Program of Dairy Goats (Capragene®). The evaluated population parameters were the effective number of founders (fe) and ancestors (fa), effective size (Ne), inbreeding coefficient (F), individual increase in inbreeding (ΔFi), average coefficient of relatedness (AR), the integrity of pedigrees and Wright's F statistics. The effect of inbreeding was verified by t test evaluating contrast through a subroutine MTDFREML application. We used pedigree data from 7,640 animals and 3,548 lactation information pertaining to 2,154 goats. The mean AR and F coefficients of the population were 1.48% and 0.78%, respectively. But the effective size was 39,69, from complete equivalent generation. The effective number of founder animals (fe) and ancestors (fa) was 123 and 101 respectively, and fiam all ancestors only 39 were responsible for explaining 50% of the genetic variability within the population, which indicates loss of source genes. As for the integrity of pedigrees were identified 80.13% animals as sires (breeders) and 79.02% as mothers. For subdivision of the population of the values obtained for FIS, FST and FIT were -0.017, 0.028 and 0.011 respectively, indicating the absence of the population structuring. There was no significant effect of inbreeding on the duration of lactation (P>0.05). The production of milk up to 305 days of lactation was significantly affected by inbreeding, with a reduction of 2.31 kg with the increase of 1% in the individual inbreeding / A raça de caprinos Saanen está presente em todos os países que têm uma caprinocultura leiteira razoavelmente desenvolvida, sendo a raça predominante nos criatórios e de maior média de produção de leite. Objetivou-se com este estudo avaliar a estrutura populacional e o efeito da endogamia sobre a produção de leite até os 305 dias de lactação e a duração da lactação em cabras da raça Saanen pertencentes a rebanhos participantes do Programa de Melhoramento Genético de Caprinos Leiteiros (Capragene®). Os parâmetros populacionais avaliados foram o número efetivo de fundadores (fe) e ancestrais (fa), tamanho efetivo (Ne), coeficiente de endogamia (F), incremento individual de endogamia (ΔFi), coeficiente médio de parentesco (AR), a integridade dos pedigrees e as estatísticas F de Wright. O efeito da endogamia foi verificado pelo teste t, avaliando-se contraste por meio de uma sub-rotina do aplicativo MTDFREML. Foram utilizados dados de pedigree de 7.640 animais e informações de 3.548 lactações pertencentes a 2.154 cabras. Os coeficientes de F e AR médios da população foram de 1,48% e 0,78%, respectivamente. Já o tamanho efetivo foi de 39,69, considerando a geração equivalente completa. O número efetivo de animais fundadores (fe) e de ancestrais (fa) foi de 123 e 101 respectivamente, o que indica perda de genes de origem. De todos os ancestrais, apenas 39 foram responsáveis por explicar 50% da variabilidade genética da população. Quanto à integridade dos pedigrees foram identificados 80,13% de animais como pais (reprodutores) e 79,02% como mães. As estatísticas F de Wright, FIS, FST e FIT, foram -0,017, 0,028 e 0,011 respectivamente, indicando a ausência de subestruturação da população. Não houve efeito significativo da endogamia sobre a duração da lactação (P>0,05). A produção de leite até os 305 dias de lactação foi afetada significativamente pela endogamia, havendo uma redução de 2,31 kg na produção de leite com o incremento de 1% na endogamia individual / 2017-01-11
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Constraints on sexual reproduction and seed set in <em>Vaccinium</em> and <em>Campanula</em>Nuortila, C. (Carolin) 05 June 2007 (has links)
Abstract
Plant reproductive success is affected by a number of factors, such as climatic conditions and plant resource status during flowering and fruiting, and pollen origin in fertilization. In the present thesis project, different aspects of plant reproductive ecology were investigated in order to identify constraints on sexual reproduction and seed set in two clonal dwarf shrubs (Vaccinium myrtillus and V. vitis-idaea) and one long-lived perennial herb (Campanula rotundifolia). The work comprised phenological observations and experiments with the clonal shrubs at natural boreal forest sites in the Oulanka National Park in northern Finland. The impact of mycorrhiza on C. rotundifolia fitness traits was tested in hand pollinations in a greenhouse experiment.
Pollen origin had some effect on fruit set, and had strong effects on the number of matured seeds in all three species. Seed yield reductions upon hand self-pollination as compared with hand cross-pollination were attributed to inbreeding depression in V. myrtillus, and presumably to partial self-incompatibility in C. rotundifolia. V. myrtillus and V. vitis-idaea showed a population structure where the number of matured seeds per fruit increased with increasing distance between pollen donor and pollen recipient. Clonal growth in concert with the foraging behaviour of bumblebee pollinators is thought to cause the possibility of either uniparental or biparental inbreeding, with a strong effect on the number of matured seeds per berry.
In a flower-removal experiment lasting three years, costs of fruiting to future fecundity and vegetative traits were observed, but not to future survival in V. vitis-idaea and V. myrtillus. The response was more pronounced in the evergreen than in the deciduous species. In Campanula rotundifolia, mycorrhiza was associated with a cost to the plants' reproductive effort, as plant biomass and the number of flowers produced per plant were decreased in mycorrhizal plants in comparison with non-mycorrhizal plants. There was no difference in seed number, seed weight or germination between the seeds of mycorrhizal and non-mycorrhizal plants. However, the offspring of mycorrhizal plants had a higher relative growth rate, while also having a higher seed phosphorus concentration.
In summary, sexual reproduction was variably constrained by previous reproduction in Vaccinium, and contrary to expectations, by mycorrhiza in Campanula. However, mycorrhiza had positive effects on some measures of offspring fitness. In all three species, self-pollination limited seed production.
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Investigation of pollen limitation, inbreeding and outbreeding depression and heterosis in Euphrasia stricta var. suecica on GotlandNilsson, Emelie January 2017 (has links)
Habitat fragmentation is one of the main threats to semi-natural grasslands all over Europe, causing reductions in both numbers of populations and numbers of individuals withinpopulations. Small isolated populations are particularly vulnerable to fluctuations that reducespopulation size and could lead to loss of genetic variation due to inbreeding depression, orfixation of harmful alleles due to genetic drift. The aim of this study was to investigate if thecritically endangered eyebright Euphrasia stricta var. suecica experiences pollen limitation,inbreeding depression and heterosis or outbreeding depression. Low pollen limitation waspredicted as well as low inbreeding depression due to high selfing rate. Outbreedingdepression or heterosis was expected based on previous studies indicating strong geneticdifferentiation among populations. This study was conducted in two traditionally managedmeadows in the central part of Gotland, Sweden, using supplemental hand-pollinations andcontrolled crosses. Individuals were collected when the flowering period was over and seedswere counted and weighed. There were no signs of either pollen limitation, inbreedingdepression, heterosis or outbreeding depression in any of the two wooded hay meadows. Thedegree of autonomous selfing was high, indicating that E. stricta var. suecica is not dependenton pollinators for seed production. A significant difference between the meadows was foundin proportion of viable seeds. As there were no signs of local adaptation, individuals could betranslocated between the two studied populations or seed sowings could be used to increasepopulation size. However, before such conservation efforts are undertaken, it is important toconduct further studies that investigate several populations including more life-stages.
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Female Dispersal and Inbreeding in the Red-cockaded WoodpeckerDaniels, Susan J. 11 September 1997 (has links)
Dispersal is a critical life-history component; it determines gene flow and has profound effects on population structure, demography, social systems, and population viability. To add to our knowledge of dispersal and, in particular, our understanding of the relationship between dispersal and inbreeding, I studied three aspects of the biology of the red-cockaded woodpecker: dispersal of breeding females; the costs, benefits, and frequency of inbreeding; and the effect of inbreeding on natal dispersal.
Dispersal of breeding female red-cockaded woodpeckers is strongly associated with inbreeding avoidance and mate choice, weakly associated with site choice, and not found to be associated with social constraints. Estimates of mortality for non-dispersing and dispersing breeding females were 24 and 59 percent per year, respectively-rare evidence of the cost of breeding dispersal.
Significant costs of close inbreeding were found. Closely related pairs (kinship coefficient greater than 0.1) had lower hatching success as well as lower survival and recruitment of fledglings than unrelated pairs. Moderately related pairs (kinship coefficient between 0 and 0.1) and moderately inbred individuals had increased hatching success, but did not produce more young.
Despite documented costs of close inbreeding and a predictable spatial distribution of closely related males near the natal territory, female fledglings disperse a median of only two territories and a modal distance of one territory. Natal dispersal of females is affected by closely related males on the natal site but unaffected by closely related males or moderately related males that are off the natal site. / Master of Science
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Costs and benefits of self-fertilization in the cleistogamous perennial Ruellia humilisTatyana Yazmine Soto (13171230) 28 July 2022 (has links)
<p> </p>
<p>The degree of self-fertilization in a population determines levels of genetic variation and high selfing rates could thus limit future adaptive potential. Theory predicts that intermediate selfing rates should not persist, yet many plants exhibit mixed mating. Cleistogamy is a floral heteromorphism where individuals produce both showy potentially outcrossing chasmogamous flowers and closed obligately selfing cleistogamous flowers. Reproduction via cleistogamous flowers is thought to be beneficial because of their greater energetic economy compared to chasmogamous flowers but can be costly if selfing leads to inbreeding depression or accelerates the fixation of deleterious mutations within populations. Cleistogamy has evolved independently multiple times and can be used to study the maintenance of adaptive mixed mating. To investigate this, I estimated the costs and benefits of selfing in three populations of <em>Ruellia humilis </em>Nutt (Acanthaceae) in greenhouse common garden experiments. To quantify the costs, I performed hand pollinations and quantified fitness components of progeny resulting from selfing and outcrossing within- and between-populations. To quantify the relative energetic advantage of cleistogamous flowers, I measured dry flower mass, fertility, seed number per fruit, and pollen-ovule ratios of both types of flowers. I found negative cumulative inbreeding depression in all populations, indicative of selfed progeny outperforming outcrossed progeny. While the fitness consequences of between population outcrossing ranged from heterosis to outbreeding depression. When looking at the energetic benefits of selfing, I found that the cost of reproduction via cleistogamous flowers was between 3 and 14-fold less than the cost for outcrossing flowers. Finally, I combined data on inbreeding depression and the energetic costs of reproduction and found that chasmogamous flowers of <em>R. humilis </em>must provide between a 3 to a 45-fold fitness advantage to be maintained, the magnitude of which was dependent upon maternal population. Overall, I conclude that none of the existing hypotheses are sufficient enough to provide the selective advantage needed to explain the persistence of chasmogamous flowers in <em>R. humilis</em>. Without any supported explanations for the maintenance of mixed mating, the exploration of genetic constraints on the loss of chasmogamous flowers could solve this long-standing mystery. </p>
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Evolution of floral and mating system variation in Camissoniopsis cheiranthifolia (Onagraceae): An evaluation of patterns and processesDart, Sara Rachel 21 January 2013 (has links)
Understanding how floral traits covary with one another and with mating patterns is an important step in understanding how and why mating systems evolve. I examined the evolution of floral and mating system variation in Camissoniopsis cheiranthifolia (Onagraceae), a species that exhibits divergence in key floral traits expected to be associated with variation in the relative importance of outcrossing vs. self-fertilization.
I combined geographic surveys of floral variation with genetic estimates of the proportion of seeds outcrossed (t) and confirmed that t covaried with corolla width and herkogamy in a predictable way both within and among populations. I then performed geographic surveys, manipulative experiments and genetic analyses to evaluate the potential role that; inbreeding depression (ID), interactions between flowers, pollinators and florivores, and reproductive assurance (RA) may have played in shaping and/or maintaining the geographic pattern of mating system variation in this species.
The main selective factor maintaining outcrossing in large flowered (LF) populations appears to be ID, which was much stronger in LF compared to small flowered (SF) populations. These results are also consistent with purging of ID in SF populations. Increased selfing appeared to alleviate pollen limitation (PL) because it was associated with higher and less variable fruit set and reduced florivory by a microlepidopteran. However, evidence that florivores preferentially attacked larger flowers was equivocal. LF experienced stronger PL than SF populations suggesting that one condition for the evolution of selfing via RA is met in outcrossing populations. Floral emasculation experiments revealed that the timing of selfing also covaried with flower size among and within populations. SF self-pollinate before flowers open but LF do not, suggesting that selfing evolved in response to chronic outcross PL. Negative side effects of emasculation were detected which prevented a clear interpretation of the RA value of selfing. Given that much of what is known about RA comes from emasculation experiments, my results suggest that the assumptions of this approach, which are rarely verified, require more serious consideration. Taken together my results suggest that C. cheiranthifolia has evolved multiple stable mixed mating systems perhaps in response to selection for RA. / Thesis (Ph.D, Biology) -- Queen's University, 2012-12-30 14:13:46.366
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The Effects of Inbreeding on Fitness Traits in the Critically Endangered Attwater’s Prairie-chickenHammerly, Susan C. 08 1900 (has links)
The goals of captive breeding programs for endangered species include preserving genetic diversity and avoiding inbreeding. Typically this is accomplished by minimizing population mean kinship; however, this approach becomes less effective when errors in the pedigree exist and may result in inbreeding depression, or reduced survival. Here, both pedigree- and DNA-based methods were used to assess inbreeding depression in the critically endangered Attwater’s prairie-chicken (Tympanuchus cupido attwateri). Less variation in the pedigree-based inbreeding coefficients and parental relatedness values were observed compared to DNA-based measures suggesting that errors exist in the pedigree. Further, chicks identified with high parental DNA-based relatedness exhibited decreased survival at both 14- and 50-days post-hatch. A similar pattern was observed in later life stages (> 50 days post-hatch) with birds released to the wild; however, the pattern varied depending on the time post-release. While DNA-based inbreeding coefficient was positively correlated with mortality to one month post-release, an opposite pattern was observed at nine months suggesting purging of deleterious alleles. I also investigated whether immunocompetence, or the ability to produce a normal immune response, was correlated with survival; however, no significant correlation was observed suggesting that inbreeding was a more important factor influencing survival. Pairing individuals for breeding by minimizing DNA-based parental relatedness values resulted in a significant increase in chick survival. This study highlights the importance of using DNA-based methods to avoid inbreeding depression when errors exist in the pedigree.
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Estudos genéticos de jatobá (Hymenaea courbaril L.) em área natural e restauração florestal com espécies nativas / Hymenaea courbaril L. (jatobá): genetic studies in natural population and forest restoration areas with native speciesPereira, Lya Carolina da Silva Mariano 09 October 2017 (has links)
O bioma Mata Atlântica tem sofrido com a fragmentação florestal e como forma de reestabelecer ambientes florestais são realizados plantios de restauração. Porém, por muito tempo houve preocupação somente com a composição florística das áreas e a diversidade genética foi negligenciada. Além disso, muitas áreas são implantadas a partir de sementes coletadas em áreas florestais geralmente pouco conservadas, pequenas e isoladas, o que pode comprometer a qualidade genética das mudas, produzindo indivíduos menos adaptados em decorrência da depressão endogâmica. Assim este trabalho teve como objetivo principal analisar o aspecto genético em áreas de restauração na região do Pontal do Paranapanema e área natural de referência, o Parque Estadual Morro do Diabo (PEMD), utilizando o jatobá (Hymenaea courbaril L.) como espécie modelo. No capítulo 1 com o objetivo de verificar a diversidade genética de H. courbaril em áreas de restauração florestal, foram selecionadas duas áreas de plantio com espécies nativas. Nestas áreas e no PEMD foram coletadas amostras foliares de indivíduos adultos que foram genotipadas para oito locos microssatélites. No PEMD ainda foram coletados frutos em 12 matrizes para caracterização do sistema reprodutivo. As três áreas estudadas apresentaram diversidade genética e níveis de endogamia similares. Nas três áreas de estudo foi identificada baixa estruturação genética espacial. Houve predomínio de fecundação cruzada para a produção de frutos na área natural, porém a taxa de cruzamentos entre indivíduos aparentados foi até dez vezes maior que a observada em outras populações da espécie. No capítulo 2 com o objetivo de verificar se há depressão endogâmica em progênies provenientes do PEMD foram selecionadas 320 sementes de 12 matrizes. Estas e seus frutos foram medidos. As plântulas a que deram origem também foram mensuradas, mensalmente, durante 15 meses. Todos os indivíduos foram genotipadas para oito locos microssatélites. A coancestria, foi estimada e os indivíduos separados em: não aparentados (tu), aparentados (tr) e autofecundação (s). Foi verificada diferença entre as métricas das plantas de acordo com o nível de coancestria entre indivíduos. Também foram estimados os valores de depressão endogâmica (ID). A quantidade de indivíduos irmãos de autofecundação foi muito pequena, sendo a maioria proveniente de cruzamento entre indivíduos não aparentados. A depressão endogâmica por autofecundação foi mais evidente no peso e tamanho dos frutos, e amena ou inexistente para os demais caracteres. Isto provavelmente por estas sementes terem sido coletadas em um fragmento grande e bem conservado e que ainda não sofre as consequências da depressão endogâmica. Assim, nosso trabalho mostrou que áreas de restauração florestal que seguiram as recomendações genéticas de implantação, apresentam diversidade genética suficiente para H. courbaril, podendo estas áreas serem fonte de coleta de sementes no futuro. E que os indivíduos provenientes de sementes do PEMD não apresentaram efeito de depressão endogâmica até 15 meses de desenvolvimento em viveiro. / The Brazilian Atlantic Forest was severely deforested and restoration initiatives are necessary to reestablish environments. However, for a long time there is only concern over floristic composition and the genetic diversity has been neglected. In addition, several restoration areas are planted from seeds collected in forest areas that are generally poorly preserved, small and isolated, which may compromise the genetic quality of the seedlings, producing less adapted individuals due to inbreeding depression. The aim of this work was to analyze the genetic aspects of Hymenaea courbaril L. in restoration areas in Pontal do Paranapanema region, and a natural reference forest, the Morro do Diabo State Park (PEMD), where seeds were also collected. In Chapter 1, to verify the genetic diversity of H. courbaril in areas of forest restoration, using eight microsatellites, two restoration areas were selected. In these areas and in the PEMD, leaf samples from adult individuals were collected. In the PEMD, fruits were collected in 12 seed trees for mating system characterization. The three areas presented similar genetic diversity and levels of inbreeding. Low spatial genetic structure was identified in the three studied areas. In the natural forest, fruits were mainly produced through outcrossings, but the rate of mating among relatives was up to ten times higher than the observed in other H. courbaril populations. In Chapter 2, to verify the inbreeding depression in the PEMD were selected 320 seeds from eight seed trees. The seeeds and their fruits were measured. The seedlings were also measured monthly, during 15 months. All seedlings were genotyped with eight microsatellite loci. From the pairwise coancestry the seedlings were separated into three categories: outcrossing among unrelated individuals (tu), outcrossing among related individuals (tr), and selfing (s). We verified differences among groups in the metrics of seedlings according to the level of coancestry among individuals. The values of inbreeding depression (ID) were also estimated. The number of selfed seedlings were very small, and the majority were from outcrossing among unrelated individuals. Inbreeding depression by selfing was more evident in weight and size fruit, and was insignificant or non-existent for other characters. This is probably because these seeds were collected in a large and preserved forest fragment, that does not suffer the consequences of inbreeding depression yet. Thus, our work showed that forest restoration areas that followed the genetic recommendations present enough genetic diversity for H. courbaril, and these areas may be a source of seeds for collection in the future. Besides that, seedlings from seed trees in PEMD did not present inbreeding depression effect up to 15 months of nursery development.
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Variabilidade genética em progênies S1 e depressão por endogamia em populações de milho (Zea mays L.) / Genetic variability in S1 progenies and inbreeding depression in maize (Zea mays L.) populationsGarbuglio, Deoclécio Domingos 25 January 2008 (has links)
Os objetivos do presente trabalho se dirigem ao estudo da variabilidade genética e da depressão por endogamia em sete populações de milho de ampla base genética, visando ao melhoramento de populações e obtenção de linhagens endogâmicas promissoras. Foram instalados onze experimentos em blocos casualizados em um local (Anhembi, SP), com diferentes conjuntos (N) de progênies S1 obtidos de sete populações (GO-D: dentado, GO-F: flint, GO-L: espiga longa, GO-G: espiga grossa; e compostos G3, G4 e GO-S). Foram estimadas a variância genética entre médias de progênies (2G), a variância fenotípica entre médias de progênies?^ (2F?^) e o coeficiente de herdabilidade (sentido amplo) para médias de progênies (2X). As estimativas de h 2Xhforam altas para peso de espigas (PE: 0,89 a 0,94), comprimento da espiga (CE: 0,77 a 0,88) e diâmtero da espiga (DE: 0,77 a 0,92); e menores para altura da planta (AP: 0,58 a 0,80) e altura da espiga (AE: 0,54 a 0,84), demonstrando alto potencial das populações para seleção recorrente com progênies S1. A variável PE nas populações base usadas como testemunha, mostrou valores variando de 11200 kg.ha-1 (GO-D) a 12800 kg.ha-1 (G3). As médias de progênies S1 entre populações variaram de 6070 kg.ha-1 (GO-F) a 7380 kg.ha-1 (G4); a depressão por endogamia nas progênies S1 variou de 37,5% (G4) a 48,0% (G3) em relação à população base. Os estudos sobre endogamia envolvendo as sete populações foram conduzidos com amostras da população original não endógama (S0) e das gerações S1 e S2 de autofecundação. Os experimentos foram conduzidos em Londrina (PR) e Piracicaba (SP) em blocos casualizados com parcelas subdivididas, com as populações representadas nas parcelas e as gerações de endogamia nas sub-parcelas. A estimação da depressão por endogamia foi obtida pelo modelo de regressão linear Y = µ0 + ?, sendo ? a depressão por endogamia para 100% de homozigose. A depressão esperada para 50% de homozigose é ?/2, cujo valor em percentagem variou de 25,4% a 41,4% em Piracicaba e de 23,1% a 39,3% em Londrina. Para os demais caracteres, os efeitos depressivos foram menores, geralmente <25% para AP e AE e <15% para DE e CE. / The objectives of the present work were directed for the study of genetic variability and inbreeding depression in seven maize populations of broad genetic base, as a guide for population improvement and development of promising inbred lines. The field evaluation was in eleven experiments (randomized complete blocks) in one location (Anhembi, SP) with different groups (N) of S1 progenies obtained of seven populations (GO-D: dent type, GO-F: flint type, GO-L: long ear, GO-G: thick ear; and composites G3, G4 e GO-S). Estimates were obtained for genetic variance (?^: progeny mean basis), phenotypic variance of progeny means (2G2F?^), and coefficient of heritability (broad sense) for progeny means (2Xh). Estimates of 2Xhwere high for ear weight (PE: 0.89 to 0.94), ear length (CE: 0.77 to 0.88) and ear diameter (DE: 0.77 to 0.92); and lower for plant height (AP: 0.58 to 0.80) and ear height (AE: 0.54 to 0.84), thus showing the high potential of the populations for recurrent selection based on S1 progenies. Ear yield (PE) in the base populations used as ckecks varied from 11200 kg.ha-1 (GO-D) to 12800 kg.ha-1 (G3). The means of S1 progenies varied from 6070 kg.ha-1 (GO-F) to 7380 kg.ha-1 (G4); the inbreeding depression in S1 progenies varied from 37.5% (G4) to 48.0% (G3) relative to the non-inbred population. For the studies on inbreeding in the seven populations samples of the original non-inbred populations (S0) and S1 and S2 generations of inbreeding were used. Filed experiments were carried out in Londrina (PR) and Piracicaba (SP) in randomized blocks with spli-plots, where populations were in the whole plots and inbreeding generations in the sub-plots. The estimates of inbreeding depression were obtained by the linear regression model Y = µ0 + ?, where ? is the iinbreeding depression for 100% homozygosity. The expected inbreeding depression for 50% homozygosity is ?/2, and the estimates in percentage varied from 25.4% to 41.4% in Piracicaba and from 23.1% to 39.3% in Londrina. For the other traits the inbreeding effects were lower, in general <25% for AP and AE and <15% for DE and CE.
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