Various models of the genetic architecture of quantitative traits have been considered to provide the basis for increased genetic progress. The finite polygenic model (FPM), which contains a finite number of unlinked polygenic loci, is proposed as an improvement to the infinitesimal model (IM) for estimating both additive and dominance variance for a wide range of genetic models. Analysis under an additive five-loci FPM by either a deterministic Maximum Likelihood (DML) or a Markov chain Monte Carlo (MCMC) Bayesian method (BGS) produced accurate estimates of narrow-sense heritability (0.48 to 0.50 with true values of h2 = 0.50) for phenotypic data from a five-generation, 6300-member pedigree simulated without selection under either an IM, FPMs containing five or forty loci with equal homozygote difference, or a FPM with eighteen loci of diminishing homozygote difference. However, reducing the analysis to a three- or four-loci FPM resulted in some biased estimates of heritability (0.53 to 0.55 across all genetic models for the 3-loci BGS analysis and 0.47 to 0.48 for the 40-loci FPM and the infinitesimal model for both the 3- and 4-loci DML analyses). The practice of cutting marriage and inbreeding loops utilized by the DML method expectedly produced overestimates of additive genetic variance (55.4 to 66.6 with a true value of sigma squared sub a = 50.0 across all four genetic models) for the same pedigree structure under selection, while the BGS method was mostly unaffected by selection, except for slight overestimates of additive variance (55.0 and 58.8) when analyzing the 40-loci FPM and the infinitesimal model, the two models with the largest numbers of loci. Changes to the BGS method to accommodate estimation of dominance variance by sampling genotypes at individual loci are explored. Analyzing the additive data sets with the BGS method, assuming a five-loci FPM including both additive and dominance effects, resulted in accurate estimates of additive genetic variance (50.8 to 52.2 for true sigma squared sub a = 50.0) and no significant dominance variance (3.7 to 3.9) being detected where none existed. The FPM has the potential to produce accurate estimates of dominance variance for large, complex pedigrees containing inbreeding, whereas the IM suffers severe limitations under inbreeding. Inclusion of dominance effects into the genetic evaluations of livestock, with the potential increase in accuracy of additive breeding values and added ability to exploit specific combining abilities, is the ultimate goal. / Master of Science

O milho-doce é um tipo especial de milho, de alto valor nutricional que acumula polissacarídeos solúveis de caráter adocicado no endosperma. O consumo deste vegetal está crescendo no Brasil. Sendo esse um dos maiores países produtores de milho do mundo, há também um enorme potencial de produção de milho-doce. Atualmente, existem 53 cultivares de milho-doce registradas no país, mas apenas uma predomina nas lavouras desta cultura. Nota-se uma demanda por novas cultivares de milho-doce adaptadas às condições tropicais, com altas produtividades e excelente qualidade dos grãos. Há também uma escassez de informações sobre a avaliação e obtenção de cultivares de milho-doce. Os objetivos deste trabalho compreenderam: (i) verificação da viabilidade da utilização de um testador com elevado nível de endogamia e mais selecionado, em relação aos testadores com menores níveis de endogamia e menos selecionados, para obtenção de testcrosses; (ii) verificação do progresso realizado nas médias dos testcrosses; (iii) estimação das correlações entre a produtividade de espigas e os componentes de produção; (iv) aplicação de um índice de seleção para caracterizar e selecionar os melhores testcrosses e (v) verificação da variância genética disponível após a seleção e autofecundação. Foram avaliadas duas populações de milho-doce, em que uma é testadora da outra. Os três tipos de testadores utilizados foram obtidos a partir de uma mistura de linhagens selecionadas da geração anterior, sendo assim eles possuíam duas etapas de seleção e três níveis de endogamia. Visando a seleção de linhagens, 176 testcrosses foram avaliados em duas épocas de plantio, em delineamento casualizado em blocos com três repetições. Foram avaliados os caracteres dias para florescimento masculino(FM), altura das plantas(AP), número de espigas comerciais(EC), produtividade das espigas comerciais(PE), comprimento das espigas(CE), diâmetro das espigas(DE) e enchimento de ponta(EP). Foram observadas diferenças significativas entre as médias dos testcrosses nas análises de variância individuais e conjuntas. As interações entre testcrosses e testadores, nas análises individuais, não apresentaram diferenças significativas, indicando que não houve mudança no ordenamento dos testcrosses quando se utilizaram diferentes testadores. Para a mesma interação, nas análises conjuntas foram estimadas as correlações de Spearman, que se mostraram, na grande maioria, significativas, ou seja, foi detectada correlação entre o ranqueamento dos testcrosses. Para todos os caracteres avaliados, os testcrosses exibiram médias iguais ou superiores à melhor testemunha. Não houve evidências claras da diminuição da variância genética dos testcrosses quando foram utilizados testadores mais endogâmicos e mais selecionados. O testador com endogamia equivalente à das linhagens testadas e mais selecionado mostrou-se tão eficiente quanto os testadores com endogamia menor e menos selecionado. Foram observados valores consideráveis para os progressos realizados nas médias dos testcrosses, na maioria superiores a 1%, quando a seleção se deu nos testadores e nas linhagens, destacando que a utilização de testadores selecionados maximiza as médias dos testcrosses. Observaram-se correlações genéticas positivas (rG≥0,556) entre a produtividade de espigas comerciais e os caracteres EC, CE, DE e EP. O índice utilizado classificou os testcrosses em relação a todos os caracteres avaliados simultaneamente e permitiu a seleção dos melhores. / Sweet corn is a special type of corn, with high nutritional value, which accumulates soluble polysaccharides in the endosperm, so it is sweeter than other types of corn. The consumption of sweet corn is increasing in Brazil. Being one of the major producers of corn in the world, there is also an enormous potential for the production of sweet corn. Currently, there are 53 sweet corn varieties registered in the country, but only one prevails in crops of this species. There is a demand for new varieties adapted to tropical conditions with high grain yield and superior grain quality. Additionally, there is not enough information about evaluation and development of sweet corn varieties for the Brazilian conditions. The goals of this project were: (i) to verify the feasibility of using a tester with high level of inbreeding and more selected in relation to testers with lower levels of inbreeding and less selected to obtain testcrosses; (ii) to verify the improvement of the testcross means; (iii) to estimate correlations between ear yield and production components; (iv) to apply a selection index to rank and select the best testcrosses and (v) to verify the genetic variance available after selection and selfing in the testcrosses. Two populations, where one was the tester of the other, were evaluated. In each cycle of selection testers were obtained from a mixture of selected inbred lines of the previous generation, leading to two levels of selection and three levels of inbreeding. For selection of inbred lines, 176 testcrosses were evaluated in two seasons, in randomized completed blocks with three replications. The traits days to male flowering (FM), plant height (AP), number of commercial ears (EC), ear yield (PE), ear length (CE), ear diameter (DE) and tip fill (EP) were evaluated. There were significant differences between testcross in the individual and the combined analysis of variance. Interactions between testcrosses and testers, from the individual analysis, in general, were not significant, indicating no change in the ranking of testcrosses when using different testers. For this interaction, from the joint analysis, Spearman\'s rank correlations were estimated and showed significance in most cases. For all variables, the testcross means were either equal to or greater than the best control. The level of selection underlying the constitution of a tester did not affect the genetic variance among testcrosses. The tester stemming from more selected inbred lines was as good as testers derived from less selected lines. There was progress in the testcross means, generally higher than 1%; the use of selected testers maximized testcross means. Positive genetic correlations (rG ≥ 0.556) were detected between ear yield and EC, CE, DE and EP traits. The selection index ranked the testcrosses for all traits evaluated simultaneously and allowed selecting the superior ones.

Liquidambar L. genus are represented with four species in the world and one of these species, Turkish sweet gum (Liquidambar orientalis Miller) is naturally found only in southwestern Turkey with limited distribution in Mugla Province. The presence of increasing threats to its genetic resources signifies the importance of studying the phylogenetic relationships and genetic diversity in this relict endemic species. In this study, 18 different populations were sampled throughout the species range and noncoding transfer ribonucleic acid (trn) region of chloroplast DNA was studied to asses the phylogenetic relationships and genetic diversity. Experimental studies included the extraction of DNA, amplification and sequencing of the trn region of the chloroplast DNA. Molecular evolutionary analysis was done by using MEGA version 3.1 and Arlequin 2.000 softwares. Sequences from six other species of Liquidambar (L. styraciflua from USA, L. macrophylla from Mexico, L. formosana from Vietnam, L. acalycina from China, L. formosana from China and L. acalycina from USA) in the database were also included in the analysis. Moleculer diversity results show that population located in Mugla-Yatagan district has the highest number of polymorphic sites among the other populations of Turkish sweet gum. Population located in Marmaris-G&uuml / nn&uuml / cek has an average genetic distance value of 0.0032 within population, being the highest within the studied populations of Turkish sweet gum. The average genetic distance within variety orientalis (0.0011) was the greatest among all the varieties, but the most separated or divergent populations were members of variety integriloba. For both varieties and geographic groups, average diversity within was found to be the greatest portion (greater than 80%) of the total sequence diversity. The geographic groups located in Denizli and Mugla-Yatagan showed the highest average genetic distances within location, with a value of 0.0014. The genetic distance between the closest neighbor of Turkish sweet gum, American L. styraciflua was 0.0002, whereas the genetic distance between the most distant neighbors (Vietnamese L. formosana, Chinese L. acalycina and L. formosana) was 0.0051. Based on the molecular diversity analysis, seven populations were found to be important for conservation issues and two of them located in Marmaris have the highest priority. The most variant geographic groups are located in Denizli and Mugla-Yatagan districts. These populations could be considered as good candidates for future in-situ or ex-situ conservation programs

More than half of the Pinaceae is including in genus Pinus covers the large parts of vegetation of northern hemisphere. The Anatolian Black Pine is one of the subspecies of European Black Pine, growing naturally as a widespread mid elevation species of Taurus, western Anatolian and northern Anatolian Mountains of Turkey. Although it is disputed that there are 5 varieties of Anatolian black pine but three of these are well recognized. These are Pinus nigra subsp. pallasiana var. pallasiana, Pinus nigra Arnold subsp. pallasiana var. pyramidata (pyrimidal black pine) and Pinus nigra Arnold subsp. pallasiana var. seneriana. To determine the genetic relationship between Anatolian black pine and its well recognized varieties, 3 different taxa of Anatolian black pine (well recognized varieties) were sampled in the natural range of species and non-coding trn regions of chloroplast DNA (cpDNA) were sequenced to assess the genetic structure of the species. Three sectors of trn region were examined. Analysis was assessed with using MEGA version 4.0 and Arlequin 2.000 softwares. Considering genetic diversity of three Anatolian black pine taxa with respect to trn regions and parsimonic sites, the result showed that P. nigra subsp pallasiana var seneriana was more polymorphic than other two taxa. Also, the most distant taxon that show differences in trn sequences when compared to other taxa was P. nigra subp pallasiana var pyramidata. The constructed phylogenetic tree showed that individuals of P.nigra subsp pallasiana var pyramidata were grouped together. However, other two taxa showed a dispersed allocation in the tree. This result indicates that var pyramidata was the most distant taxon. According to present study, there is no clear speciation between varieties and var pallasiana. The differences between them may be a result of mutation which may have occured in the genes coding for growth and form of Anatolian black pine.

The genus Picea is located from temperate to Taiga (boreal) regions of northern hemisphere from subtropical to high altitude with 34 species. Picea orientalis is endemic to Eastern Black Sea Mountainous region of Turkey and Western Caucasus. To determine the genetic relatedness within Picea orientalis populations, as well as the relationship between other Pinaceae species from database, populations were sampled from 15 different locations within the natural range of species and grouped into 5 depending on several criteria. In order to evaluate the genetic structure of the taxon, non-coding trn and matK regions of choloroplast DNA (cpDNA) were sequenced. According to genetic diversity analysis of 15 Picea orientalis populations with respect to trn and matK regions, there is not much variation among populations. Among 3 non-coding trn and the matK region, there is only one variable site which was parsimony informative. The results indicated that the populations from Artvin had the highest divergence. In this study, the genetic divergence of Picea orientalis from other Pinaceae species were also observed. According to the results obtained from trnV region the studied Picea orientalis observed to display a close relationship with Larix and distinct from other Pinaceae especially Pinus genus. This result is unrepresentative due to the results of other studies. Moreover, as a result of analysis with trncd-ef region, the studied Picea orientalis populations possessed close relationship with species from clade Picea. Moreover, based on molecular clock estimations the studied Picea orientalis populations had close relationships with the species form Asia. Finally, the relationship of Picea orientalis with other Picea species were analyzed with respect to matK region. The result is consistent with the results of trncd-ef region and also with other studies.

During the last decades the climate has been changing more rapidly than in the preceding periods. This is for instance characterized by an increase in temperature. Interestingly, such changes in the environment are not necessarily constant over time as they often show high levels of fluctuation. Organisms are exposed to these changes and respond to them and a recent theoretical model predicts that fluctuations in the environment are important for populations’ response to climate change. The aim of this thesis is to investigate how populations respond to a changing environment, including fluctuations. My thesis is based on the previously mentioned theoretical model and I used a suite of laboratory experiments on the seed beetle Callsosobruchus maculatus, to test the model predictions in a quantitative genetic framework. First, I assessed the genetic architecture of several life history and morphological traits in order to verify that there is sufficient additive genetic variation for the population to respond to changes in the environment. Second, I tested the detailed model predictions explicitly, by investigating whether different types of environmental fluctuations matter for a population’s response. Third, I investigated changes in quantitative genetic variation after i) a rapid shift in temperature and ii) long term selection under increasing temperature including fluctuations. Fourth, I concentrated on sex differences in response to temperature, and finally, I assessed the relative importance of genetic and nongenetic inheritance for traits that differ in their plastic response to a change in the environment. I found that environmental fluctuations are highly important for a population’s response to environmental change. I could detect changes in a set of quantitative genetic parameters, suggesting that a population’s potential to respond to selection, environmental sensitivity and the evolution of phenotypic plasticity are affected by the selective past. I also found that sexes differ in additive genetic variation and plasticity and that parental effects may play an important role in the evolutionary process. Therefore, future studies would benefit greatly from considering details of the selective past and especially environmental fluctuations during attempts to predict how populations respond to a changing environment, particularly with regards to climate change.

O milho-doce é um tipo especial de milho, de alto valor nutricional que acumula polissacarídeos solúveis de caráter adocicado no endosperma. O consumo deste vegetal está crescendo no Brasil. Sendo esse um dos maiores países produtores de milho do mundo, há também um enorme potencial de produção de milho-doce. Atualmente, existem 53 cultivares de milho-doce registradas no país, mas apenas uma predomina nas lavouras desta cultura. Nota-se uma demanda por novas cultivares de milho-doce adaptadas às condições tropicais, com altas produtividades e excelente qualidade dos grãos. Há também uma escassez de informações sobre a avaliação e obtenção de cultivares de milho-doce. Os objetivos deste trabalho compreenderam: (i) verificação da viabilidade da utilização de um testador com elevado nível de endogamia e mais selecionado, em relação aos testadores com menores níveis de endogamia e menos selecionados, para obtenção de testcrosses; (ii) verificação do progresso realizado nas médias dos testcrosses; (iii) estimação das correlações entre a produtividade de espigas e os componentes de produção; (iv) aplicação de um índice de seleção para caracterizar e selecionar os melhores testcrosses e (v) verificação da variância genética disponível após a seleção e autofecundação. Foram avaliadas duas populações de milho-doce, em que uma é testadora da outra. Os três tipos de testadores utilizados foram obtidos a partir de uma mistura de linhagens selecionadas da geração anterior, sendo assim eles possuíam duas etapas de seleção e três níveis de endogamia. Visando a seleção de linhagens, 176 testcrosses foram avaliados em duas épocas de plantio, em delineamento casualizado em blocos com três repetições. Foram avaliados os caracteres dias para florescimento masculino(FM), altura das plantas(AP), número de espigas comerciais(EC), produtividade das espigas comerciais(PE), comprimento das espigas(CE), diâmetro das espigas(DE) e enchimento de ponta(EP). Foram observadas diferenças significativas entre as médias dos testcrosses nas análises de variância individuais e conjuntas. As interações entre testcrosses e testadores, nas análises individuais, não apresentaram diferenças significativas, indicando que não houve mudança no ordenamento dos testcrosses quando se utilizaram diferentes testadores. Para a mesma interação, nas análises conjuntas foram estimadas as correlações de Spearman, que se mostraram, na grande maioria, significativas, ou seja, foi detectada correlação entre o ranqueamento dos testcrosses. Para todos os caracteres avaliados, os testcrosses exibiram médias iguais ou superiores à melhor testemunha. Não houve evidências claras da diminuição da variância genética dos testcrosses quando foram utilizados testadores mais endogâmicos e mais selecionados. O testador com endogamia equivalente à das linhagens testadas e mais selecionado mostrou-se tão eficiente quanto os testadores com endogamia menor e menos selecionado. Foram observados valores consideráveis para os progressos realizados nas médias dos testcrosses, na maioria superiores a 1%, quando a seleção se deu nos testadores e nas linhagens, destacando que a utilização de testadores selecionados maximiza as médias dos testcrosses. Observaram-se correlações genéticas positivas (rG≥0,556) entre a produtividade de espigas comerciais e os caracteres EC, CE, DE e EP. O índice utilizado classificou os testcrosses em relação a todos os caracteres avaliados simultaneamente e permitiu a seleção dos melhores. / Sweet corn is a special type of corn, with high nutritional value, which accumulates soluble polysaccharides in the endosperm, so it is sweeter than other types of corn. The consumption of sweet corn is increasing in Brazil. Being one of the major producers of corn in the world, there is also an enormous potential for the production of sweet corn. Currently, there are 53 sweet corn varieties registered in the country, but only one prevails in crops of this species. There is a demand for new varieties adapted to tropical conditions with high grain yield and superior grain quality. Additionally, there is not enough information about evaluation and development of sweet corn varieties for the Brazilian conditions. The goals of this project were: (i) to verify the feasibility of using a tester with high level of inbreeding and more selected in relation to testers with lower levels of inbreeding and less selected to obtain testcrosses; (ii) to verify the improvement of the testcross means; (iii) to estimate correlations between ear yield and production components; (iv) to apply a selection index to rank and select the best testcrosses and (v) to verify the genetic variance available after selection and selfing in the testcrosses. Two populations, where one was the tester of the other, were evaluated. In each cycle of selection testers were obtained from a mixture of selected inbred lines of the previous generation, leading to two levels of selection and three levels of inbreeding. For selection of inbred lines, 176 testcrosses were evaluated in two seasons, in randomized completed blocks with three replications. The traits days to male flowering (FM), plant height (AP), number of commercial ears (EC), ear yield (PE), ear length (CE), ear diameter (DE) and tip fill (EP) were evaluated. There were significant differences between testcross in the individual and the combined analysis of variance. Interactions between testcrosses and testers, from the individual analysis, in general, were not significant, indicating no change in the ranking of testcrosses when using different testers. For this interaction, from the joint analysis, Spearman\'s rank correlations were estimated and showed significance in most cases. For all variables, the testcross means were either equal to or greater than the best control. The level of selection underlying the constitution of a tester did not affect the genetic variance among testcrosses. The tester stemming from more selected inbred lines was as good as testers derived from less selected lines. There was progress in the testcross means, generally higher than 1%; the use of selected testers maximized testcross means. Positive genetic correlations (rG ≥ 0.556) were detected between ear yield and EC, CE, DE and EP traits. The selection index ranked the testcrosses for all traits evaluated simultaneously and allowed selecting the superior ones.

A epistasia já é conhecida desde o início dos estudos em genética, porém sua contribuição para as estimativas dos componentes da variância genética e para o melhoramento genético ainda não é bem entendida. A maioria dos modelos usados para estudar a herança dos caracteres quantitativos considera apenas os efeitos genéticos aditivos e de dominância, assumindo ausência da epistasia, mesmo que as análises não forneçam testes para tal suposição. Portanto, na sua presença, estimativas de variância aditiva e dominância, coeficientes de herdabilidade e respostas esperadas com a seleção estão viesadas. Os objetivos deste estudo foram: (i) verificar se a epistasia está presente na expressão de diversos caracteres em testecrosses; (ii) estimar os efeitos epistáticos em cada planta 2 F para estes caracteres; e (iii) verificar se a epistasia interage com ambientes e testadores. Uma população de 100 progênies F2:3 foi obtida do cruzamento das linhagens endogâmicas L-08-05F e L-38-05D e foram retrocruzadas com as linhagens parentais e sua geração 1 F , conforme o delineamento triple test cross. As 300 progênies de retrocruzamento foram cruzadas com as linhagens testadoras L-02-03D e L-04-05F. Os testecrosses obtidos foram avaliados em dez ambientes no município de Piracicaba, SP, em delineamento látice a no esquema fatorial com duas repetições por ambientes. Os caracteres avaliados foram produção de grãos, prolificidade, acamamento e quebramento de plantas, florescimento masculino e feminino, intervalo entre florescimentos, altura de planta e espiga e posição relativa da espiga. A presença de epistasia foi detectada para todos os caracteres nos testecrosses de ambos testadores, exceto para acamamento e quebramento de plantas em que a epistasia foi observada somente nos testecrosses provenientes do testador L-04-05F. Cada testador detectou efeitos epistáticos em diferentes grupos de plantas 2 F e estes não foram unidirecionais para todos os caracteres avaliados. A interação epistasia por testador foi significativa para todos os caracteres, enquanto que a interação epistasia x ambientes não foi observada para nenhum caráter em ambos testadores. A presença de desequilíbrio de ligação na população foi observada para todos os caracteres, exceto para acamamento e quebramento. As estimativas dos componentes de variância e dos coeficientes de herdabilidade diferiram significativamente de zero, com exceção dos parâmetros estimados para os testecrosses do testador L-04-05F para o caráter acamamento e quebramento. Os resultados sugerem que as estimativas da variância aditiva e dos coeficientes de herdabilidade para aqueles caracteres nos quais foi verificada a presença de epistasia estarão viesados, caso a epistasia seja desconsiderada. Além disso, a presença de desequilíbrio de ligação na população gera vieses adicionais nas estimativas desses parâmetros. / Epistasis has been known since the beginning of the genetics studies. However its contribution to genetic variance components and to plant breeding is not well understood. Most of the genetic models designed to study the inheritance of the quantitative traits consider the absence of epistasis although most of these analyses dont provide test for such assumption. Therefore in its presence estimates of additive and dominance variances, heritability coefficients and selection responses would be biased. The objectives of this study were: (i) to verify whether epistasis is significant to the expression of several traits in testcrosses; (ii) to estimate the epistatic effects in individual 2 F plants for these traits; and (iii) to verify whether epistasis interacts with environment and with testers. A population of 100 3 : 2 F progenies from the cross of inbred lines L-08-05F and L-38-05D were backcrossed to the parental lines and their 1 F following the triple test cross design. The 300 backcrossed progenies were testcrossed to the inbred lines L-02-03D and L-04-05F. The 600 testcrosses were grown at ten environments in Piracicaba, SP, using the látice a design on a factorial scheme with two replications per environment. The traits recorded were grain yield, prolificacy, root and stalk lodging, days to anthesis, days to silk emergence, anthesis-silking interval, plant height, ear height and ear placement. Epistasis was detected for all traits in both testcrosses, but for root and stalk lodging epistasis was detected only in the testcrosses from L-04-05F tester. Each tester detected epistasis in different groups of 2 F plants, and the epistatic effects were not unidirectional for all traits. The epistasis by tester interaction was significant for all traits in both testers, but epistasis by environment interaction was not significant for all traits. Also linkage disequilibrium in the population was detected for all traits, except for root and stalk lodging. Estimates of variance components and heritability coefficients were all significant, except for testcrosses from L-04-05F tester for root and stalk lodging. The results suggested that the estimates of additive variance and heritability coefficients will be biased if the epistasis be unconsidered. Moreover the presences of linkage disequilibrium produce additional biases in the estimative theses parameters.

A trait must genetically correlate with fitness in order to evolve, however, theory suggests that strong directional selection should erode additive genetic variance (Va) in fitness and limit future evolutionary potential. Sexual antagonism and temporal fluctuations in selection are mechanisms that could maintain Va in fitness. Maternal genetic effects could be an additional source of adaptive genetic variation. I used ‘animal models’ to examine a long-term population of red squirrels to determine 1) if either sexual antagonism or temporal fluctuations in selection were maintaining direct Va in fitness or 2) if maternal genetic effects were a source of indirect Va in fitness. While there were environmental trade-offs on juvenile survival, neither sexual antagonism nor temporal fluctuations in selection maintained Va in fitness. Maternal genetic effects on fitness were significant and provide the Va in fitness needed for rapid microevolution. This is the first instance of maternal genetic effects demonstrated as the only genetic variance available for microevolution. / Northern Scientific Training Program, the Arctic Institute of North America, American Society of Mammologists, Queen Elizabeth II Graduate Scholarship in Science and Technology, NSERC Discovery (to Andrew McAdam), NSF (to Andrew McAdam)

A epistasia já é conhecida desde o início dos estudos em genética, porém sua contribuição para as estimativas dos componentes da variância genética e para o melhoramento genético ainda não é bem entendida. A maioria dos modelos usados para estudar a herança dos caracteres quantitativos considera apenas os efeitos genéticos aditivos e de dominância, assumindo ausência da epistasia, mesmo que as análises não forneçam testes para tal suposição. Portanto, na sua presença, estimativas de variância aditiva e dominância, coeficientes de herdabilidade e respostas esperadas com a seleção estão viesadas. Os objetivos deste estudo foram: (i) verificar se a epistasia está presente na expressão de diversos caracteres em testecrosses; (ii) estimar os efeitos epistáticos em cada planta 2 F para estes caracteres; e (iii) verificar se a epistasia interage com ambientes e testadores. Uma população de 100 progênies F2:3 foi obtida do cruzamento das linhagens endogâmicas L-08-05F e L-38-05D e foram retrocruzadas com as linhagens parentais e sua geração 1 F , conforme o delineamento triple test cross. As 300 progênies de retrocruzamento foram cruzadas com as linhagens testadoras L-02-03D e L-04-05F. Os testecrosses obtidos foram avaliados em dez ambientes no município de Piracicaba, SP, em delineamento látice a no esquema fatorial com duas repetições por ambientes. Os caracteres avaliados foram produção de grãos, prolificidade, acamamento e quebramento de plantas, florescimento masculino e feminino, intervalo entre florescimentos, altura de planta e espiga e posição relativa da espiga. A presença de epistasia foi detectada para todos os caracteres nos testecrosses de ambos testadores, exceto para acamamento e quebramento de plantas em que a epistasia foi observada somente nos testecrosses provenientes do testador L-04-05F. Cada testador detectou efeitos epistáticos em diferentes grupos de plantas 2 F e estes não foram unidirecionais para todos os caracteres avaliados. A interação epistasia por testador foi significativa para todos os caracteres, enquanto que a interação epistasia x ambientes não foi observada para nenhum caráter em ambos testadores. A presença de desequilíbrio de ligação na população foi observada para todos os caracteres, exceto para acamamento e quebramento. As estimativas dos componentes de variância e dos coeficientes de herdabilidade diferiram significativamente de zero, com exceção dos parâmetros estimados para os testecrosses do testador L-04-05F para o caráter acamamento e quebramento. Os resultados sugerem que as estimativas da variância aditiva e dos coeficientes de herdabilidade para aqueles caracteres nos quais foi verificada a presença de epistasia estarão viesados, caso a epistasia seja desconsiderada. Além disso, a presença de desequilíbrio de ligação na população gera vieses adicionais nas estimativas desses parâmetros. / Epistasis has been known since the beginning of the genetics studies. However its contribution to genetic variance components and to plant breeding is not well understood. Most of the genetic models designed to study the inheritance of the quantitative traits consider the absence of epistasis although most of these analyses dont provide test for such assumption. Therefore in its presence estimates of additive and dominance variances, heritability coefficients and selection responses would be biased. The objectives of this study were: (i) to verify whether epistasis is significant to the expression of several traits in testcrosses; (ii) to estimate the epistatic effects in individual 2 F plants for these traits; and (iii) to verify whether epistasis interacts with environment and with testers. A population of 100 3 : 2 F progenies from the cross of inbred lines L-08-05F and L-38-05D were backcrossed to the parental lines and their 1 F following the triple test cross design. The 300 backcrossed progenies were testcrossed to the inbred lines L-02-03D and L-04-05F. The 600 testcrosses were grown at ten environments in Piracicaba, SP, using the látice a design on a factorial scheme with two replications per environment. The traits recorded were grain yield, prolificacy, root and stalk lodging, days to anthesis, days to silk emergence, anthesis-silking interval, plant height, ear height and ear placement. Epistasis was detected for all traits in both testcrosses, but for root and stalk lodging epistasis was detected only in the testcrosses from L-04-05F tester. Each tester detected epistasis in different groups of 2 F plants, and the epistatic effects were not unidirectional for all traits. The epistasis by tester interaction was significant for all traits in both testers, but epistasis by environment interaction was not significant for all traits. Also linkage disequilibrium in the population was detected for all traits, except for root and stalk lodging. Estimates of variance components and heritability coefficients were all significant, except for testcrosses from L-04-05F tester for root and stalk lodging. The results suggested that the estimates of additive variance and heritability coefficients will be biased if the epistasis be unconsidered. Moreover the presences of linkage disequilibrium produce additional biases in the estimative theses parameters.