Comparative genetic linkage maps of Eucalyptus grandis, Eucalyptus globulus and their F1 hybrid based on a double pseudo-backcross mapping approach

Comparative genetic mapping in interspecific pedigrees presents a powerful approach to study genetic differentiation, genome evolution and reproductive isolation in diverging species. We used this approach for genetic analysis of an F1 hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and Eucalyptus globulus (Labill.). This wide interspecific cross is characterized by hybrid inviability and hybrid abnormality. Approximately 20% of loci in the genome of the F1 hybrid are expected to be hemizygous due to a difference in genome size between E. grandis (640 Mbp) and E. globulus (530 Mbp). We investigated the extent of colinearity between the two genomes and the distribution of hemizygous loci in the F 1 hybrid using high-through-put, semi-automated AFLP marker analysis. Two pseudobackcross families (backcrosses of an F1 individual to non-parental individuals of the parental species) were each genotyped with more than 800 AFLP markers. This allowed construction of de novo comparative genetic linkage maps of the F1 hybrid and the two backcross parents. All shared AFLP marker loci in the three single-tree parental maps were found to be colinear and little evidence was found for gross chromosomal rearrangements. Our results suggest that hemizygous AFLP loci are dispersed throughout the E. grandis chromosomes of the F1 hybrid.