Using RAPDs to Detect QTLs in an Interspecific F2 Hybrid of Eucalyptus

The inheritance and linkage relationships of Random Amplitied Polymorphic DNA (RAPD) markers were examined in seedlings of an interspecific hybrid between Eucalyptus gunnii and E. globulus ssp. globulus. One hundred and ten RAPD markers were scored from 71 F2, 11 F1 and 10 backcrosses to E. gunnii. Nineteen percent of the RAPD markers showed disturbed segregation in the F2, with most having a deficiency of E. globuluc bands (13 out of 18). The F2 had high levels of morphological abnormalities and poor growth compared to parental controls.F1 and outcrossed F2 progenies. Linkage analysis revealed fifteen linkage groups of three or more markers, 8 pairs and 13 unlinked markers LOD < 3.0). Markers with disturbed segregation were clustered together. One normally segregating marker (U63-695) was significantly associated with abnormal leaf morphology, branching and frost tolerance. A significant proportion (ANOVA R2=18.5%) of the variation in frost tolerance in the F2 was explained by the marker. However, abnormal leaf morphology and frost tolerance were not correlated. While interspecific hybridisation may be a powerful means of generating large amounts of genetic variation, the detection and exploitation of QTLs may be complicated by large and deleterious pleiotropic gene effects and biased by distorted segregation.