Genetic architecture of hybrid fitness and wood quality traits in a wide interspecific cross of Eucalyptus tree species

The genetic architecture of interspecific differentiation plays a key role in the evolution of reproductive isolating barriers in plants, and has important implications for hybrid breeding programs. The aim of this research project was to determine the genetic architecture of hybrid fitness and wood property traits in a cross between Eucalyptus grandis and E. globulus, two commercially important hardwood tree species. This cross combines the superior growth and adaptability of E. grandis with excellent wood properties of E. globulus. However, large amounts of F₁ hybrid inviability and F₂ hybrid breakdown are present in the progeny of this wide interspecific cross.; A pseudo-backcross mapping approach was used to generate comparative, amplified fragment length polymorphism (AFLP) genetic maps of a single superior F₁ hybrid tree and of two backcross parents. More than 1200 AFLP marker loci were analyzed. Eleven comparative synteny groups were obtained and the genetic maps of the two pure species trees and the F₁ hybrid were essentially colinear. Approximately 30% of AFLP markers were significantly distorted from expected segregation ratios and mapped to specific regions of the parental maps. The mapping data were used to estimate the position and effect of putative segregation distorting loci (SDL). At least six SDL were located in the genetic maps of the F₁ hybrid, and donor alleles were found to be favored in several of these genomic regions.; 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 NIR spectral data, predicted wood properties and AFLP genotypes were used for quantitative trait locus (QTL) analysis. A total of 18 QTLs for 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 NIR spectral variation. These QTL may represent key genetic loci that are involved in the genetic differentiation of wood properties between these two species.