Publicação
Impacto do grau de consanguinidade na descendência de um pomar de produção de sementes de polinização aberta de Eucalyptus globulus
| Resumo: | Eucalyptus globulus is a pulpwood species of outmost importance in Portugal. Open pollinated orchards are a low-cost and frequently used commercial solution for improved seed production. However, they can present disadvantages, particularly the presence of high levels of inbreeding in the seed, which reduces genetic variability and increases homozygosity, hence promoting the expression of depressive phenotypes in the offspring. The impact of the degree of inbreeding – represented by the inbreeding coefficient (F) – on the productivity of trees from different progenies in an open pollinated seed orchard was studied. Additionally, descendant trees from the seed orchard that presented abnormal morphologies were investigated, and one of the aims of this study was to perceive if this was associated with inbreeding. A total of 324 plants aged between 1.6 and 2.6 years, from 11 orchard mother trees, were analysed with small sequence repeats (SSRs), using 12 previously tested markers. Paternity tests were carried out to determine the parentage, in order to calculate the inbreeding coefficient and investigate if the parents had any degree of kinship. The plant heights were also measured and a linear mixed model including several variables (heights, F, mothers, field) was applied to perceive the impact of the degree of inbreeding on the offspring. Phenotypes related to morphology were identified in the field as normal or abnormal, in order to perform a chi-square test and understand if there was a dependency between this variable and the inbreeding coefficient. At a population level, the productivity of the offspring showed a negative trend as inbreeding increased (estimate = -0.957). A self-pollinated plant (F = 0.5) presented, on average, 40 cm less height than an outcross plant. It may seem an insignificant value, however it is important to remember that plants are in their early years, having a greater impact on the competition for sunlight and nutrients. The offspring from each mother showed a variation related to the population model, maintaining however a negative trend. There were mothers with offspring less influenced by inbreeding (minimum estimate = -0.515) and others that were highly influenced (maximum estimate = -1.486) suggesting some mothers may have inherited more deleterious mutations than others. As far as abnormal phenotypes are concerned, no inbreeding-related dependency was found (χ2(4) = 2.4277; p = 0.6576). Nevertheless, there seems to be an indication that certain crosses developed a higher percentage of offspring with these traits. This study suggests that the trees in the orchard have a variable performance when undergoing inbreeding. Thus, the latter is a relevant characteristic to be analysed in the construction and management of an improved seed orchard, in order to minimise the impact of this disadvantage inherent to open pollinated orchards. |
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| Autores principais: | Faia, João Pedro Osório |
| Assunto: | Eucalyptus globulus Consanguinidade SSRs Melhoramento genético Polinização aberta Teses de mestrado - 2020 |
| Ano: | 2020 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | português |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Eucalyptus globulus is a pulpwood species of outmost importance in Portugal. Open pollinated orchards are a low-cost and frequently used commercial solution for improved seed production. However, they can present disadvantages, particularly the presence of high levels of inbreeding in the seed, which reduces genetic variability and increases homozygosity, hence promoting the expression of depressive phenotypes in the offspring. The impact of the degree of inbreeding – represented by the inbreeding coefficient (F) – on the productivity of trees from different progenies in an open pollinated seed orchard was studied. Additionally, descendant trees from the seed orchard that presented abnormal morphologies were investigated, and one of the aims of this study was to perceive if this was associated with inbreeding. A total of 324 plants aged between 1.6 and 2.6 years, from 11 orchard mother trees, were analysed with small sequence repeats (SSRs), using 12 previously tested markers. Paternity tests were carried out to determine the parentage, in order to calculate the inbreeding coefficient and investigate if the parents had any degree of kinship. The plant heights were also measured and a linear mixed model including several variables (heights, F, mothers, field) was applied to perceive the impact of the degree of inbreeding on the offspring. Phenotypes related to morphology were identified in the field as normal or abnormal, in order to perform a chi-square test and understand if there was a dependency between this variable and the inbreeding coefficient. At a population level, the productivity of the offspring showed a negative trend as inbreeding increased (estimate = -0.957). A self-pollinated plant (F = 0.5) presented, on average, 40 cm less height than an outcross plant. It may seem an insignificant value, however it is important to remember that plants are in their early years, having a greater impact on the competition for sunlight and nutrients. The offspring from each mother showed a variation related to the population model, maintaining however a negative trend. There were mothers with offspring less influenced by inbreeding (minimum estimate = -0.515) and others that were highly influenced (maximum estimate = -1.486) suggesting some mothers may have inherited more deleterious mutations than others. As far as abnormal phenotypes are concerned, no inbreeding-related dependency was found (χ2(4) = 2.4277; p = 0.6576). Nevertheless, there seems to be an indication that certain crosses developed a higher percentage of offspring with these traits. This study suggests that the trees in the orchard have a variable performance when undergoing inbreeding. Thus, the latter is a relevant characteristic to be analysed in the construction and management of an improved seed orchard, in order to minimise the impact of this disadvantage inherent to open pollinated orchards. |
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