Genetic Architecture of Hybrid Fitness and Wood Quality Traits in a Wide Interspecific Cross of Eucalyptus Tree Species
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2001-07-24
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The genetic architecture of interspecific differentiation plays a key role in the evolution ofreproductive isolating barriers in plants, and has important implications for hybrid breeding programs. Interspecific hybridization is an important approach towards the genetic improvementof Eucalyptus tree plantations. However, incompatibilities between diverged eucalypt genomes often lead to reduced fitness of interspecific hybrids and decrease the efficiency of hybridbreeding programs. Furthermore, very little information is available on the genetic control ofquantitative traits in interspecific hybrids of Eucalyptus tree species.The aim of this project was to obtain a detailed description of the genetic architecture ofhybrid fitness and wood property traits in an interspecific cross between two commerciallyimportant hardwood tree species, E. grandis and E. globulus spp. globulus. This cross combines the superior growth and adaptability of E.globulus. The two species are members of different sections of the subgenus Symphyomyrtus andhybrid generations of this wide cross are characterized by large amounts of F hybrid inviability and F hybrid breakdown.Two interspecific backcross families of E. grandis x E. globulus were each genotyped withmore than 800 amplified fragment length polymorphism (AFLP) markers using a new high-throughput protocol for AFLP analysis on automated DNA sequencers. A pseudo-backcrossmapping approach was used to generate detailed comparative genetic maps of a single superior F hybrid tree and of two backcross parents. The genetic maps of the two pure species parents andthe F hybrid were colinear and 11 comparative synteny groups were characterized. Overall recombination rates did not differ significantly, although heterogeneity in recombination rateswas observed in several map regions. Approximately 30% of the AFLP markers were significantly distorted from expected segregation ratios. The distorted markers were located in specific map regions and distortion washighly directional in these regions. A Bayesian Markov chain Monte Carlo approach was used to estimate the position and effect of genetic factors that cause segregation distortion. At least six segregation distorting loci (SDL) were located in the genetic maps of the F hybrid. Two SDL were detected in the genome of the E.globulus backcross parent. Donor alleles were found to be favored in the recurrent genetic background at several SDL in the maps of the F hybrid. Marker-assisted breeding based ondetailed, whole-genome genotypes of hybrids may be useful to minimize the effect of hybrid breakdown factors in further generations of this cross.Near-infrared (NIR) analysis was used to predict wood property trait values for approximately 270 individuals of each backcross family after two years of growth in a field site. The trait data and AFLP genotypes were used for QTL detection and analysis in the parental genetic maps. Inaddition, a principal component analysis was performed on the NIR spectral data of eachbackcross family and the data used to map QTLs for NIR spectral variation. A total of 18 QTLsfor NIR predicted wood properties and NIR spectral variation were characterized in the parental maps of the E. globulus BC family while 13 QTLs were detected in the E. grandis BC family. Many of the QTLs had effects on multiple, correlated wood property traits and on raw NIRspectral variation. Individual principal components of NIR spectral variation were correlated withgroups of chemical and physical wood properties, and shared several large-effect QTLs with theindividual wood properties. These QTL may represent key genetic loci that are involved in thegenetic differentiation of wood properties between these two species.
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PhD
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Genetics
