COMPARATIVE GENETIC MAPPING IN INTERSPECIFIC BACKCROSS FAMILIES OF Eucalyptus USING AFLP MARKERS

Forest Biotechnology Group, Department of Forestry, NC State University, Raleigh, NC 27695 USA

We are investigating the genetic control of wood properties in Eucalyptus, a genus that includes the most widely planted hardwood tree species in the world. Wide interspecific crosses of E. grandis (high lignin, low wood density) and E. globulus (low lignin, high wood density) parents were made to obtain a large number of F₁ progeny. An exceptional F₁ individual (hybrid A1) was crossed to non-parental trees in the two parental species to obtain two interspecific backcross families of approximately 350 individuals each. We are using a new ("three-way pseudo testcross" or "pseudo backcross") mapping approach to construct high-resolution comparative AFLP genetic maps of the E. grandis and E. globulus backcross parents and of the A1 hybrid tree. This will allow us to test the effect of E. globulus alleles segregating in a E. grandis genetic background and vice versa, and will allow us to investigate the genetic basis of interspecific differences in wood properties between these two species. In addition, this approach will allow us to obtain haplotype maps of the E. grandis and E. globulus gametes that produced the fastest growing F₁ tree in a large F₁ progeny set. The AFLP maps will be used as frameworks for mapping candidate genes and quantitative trait loci (QTLs) for wood properties in these trees. The backcross families will also be useful for mapping loci contributing to hybrid vigor and hybrid dysgenesis observed in this wide interspecific cross.