Melhoramento genético de Corymbia torelliana: parâmetros genéticos e caracterização molecular de progênies

Abstract

The silviculture of the genus Corymbia in Brazil shows high productive potential, particularly for the production of charcoal and energy biomass. However, it still lacks established genetic improvement programs and superior genetic materials adapted to national soil and climatic conditions. Among the species, Corymbia torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson stands out as a strategic choice, both for its silvicultural performance and for serving as a preferred parent in the creation of highly productive interspecific hybrids tolerant to biotic and abiotic stresses. Therefore, the objective was to evaluate the genetic potential of Corymbia torelliana progenies by estimating genetic growth parameters, characterizing selected progenies at the molecular level, and seeking guidance for establishing seed orchards to continue the species' genetic improvement program. The central hypothesis was that sufficient genetic variation exists to continue a genetic improvement program for the species. The thesis is structured into four main parts: (i) a theoretical framework establishing the basis for the species' silvicultural potential and the concepts of forest breeding, quantitative genetics, and molecular genetics; (ii) Chapter 1 (Article 1), addressing the estimation of genetic parameters and correlations between growth traits in C. torelliana progenies during the establishment phase; and (iii) Chapter 2 (Article 2), covering the molecular characterization of selected progenies using microsatellite markers, followed by (iv) the thesis's Final Considerations. In the first chapter, growth traits were evaluated in a C. torelliana progeny test using linear mixed models via REML/BLUP (Restricted Maximum Likelihood / Best Linear Unbiased Prediction). The results demonstrated vigorous tree growth and significant genotypic variation in diameter at breast height. Estimates of heritability and selection accuracy were of moderate magnitude, indicating significant potential for response to selection. Genetic correlations between traits and between evaluation ages were mostly positive and of high magnitude. However, they did not yield sufficient indirect selection accuracy (ASI) to make indirect selection across ages and silvicultural traits feasible. In the second chapter, molecular characterization was performed using microsatellite (SSR) markers, enabling the assessment of diversity, dissimilarity, and genetic structure among individuals selected to form future seed orchards. The results indicated limited levels of genetic diversity, yet sufficient dissimilarity and intra-progeny structure to support controlled mating strategies and the maintenance of genetic diversity across selection cycles, thereby guiding the establishment of second-generation seed orchards (PSG) and clonal seed orchards (PCS). Taken together, and following the technical-scientific guidelines highlighted during the study, the results confirmed the potential of C. torelliana for genetic improvement programs aimed at timber production in the Campo das Vertentes region. Thus, it was demonstrated that the species possesses a suitable genetic base for selection, conservation, and recombination, contributing to the diversification of Brazil's forestry base and the sustainability of the forestry sector.