STRUCTURE OF THE SPECIFIC COMBINING ABILITY BETWEEN 2 SPECIES OF EUCALYPTUS .1. RAPD DATA

Within the context of the reciprocal recurrent selection scheme develo ped in 1989 by CIRAD-Foret on Eucalyptus, RAPD essays were performed t o assess the genetic diversity in the two species E. urophylla and E. grandis. The molecular markers were split into two parts: the specific markers (present with different frequencies in the two species) and t he common markers (present with similar frequencies in the two species ). The study analyses the structure of genetic diversity within and be tween the two species of Eucalyptus. Different genetic distances are w orked out for use in prediction equations of the individual tree trunk volume of hybrids at 38 months. Each distance is expressed as the sum of the general genetic distance and the specific genetic distance. Th e general genetic distance based on the double presence plus the doubl e absence of bands seems to be an interesting co-variate to use in a f actor regression model. Through this model the distance calculated bet ween species explains the general combining ability (GCA) and the spec ific combining ability (SCA) of the phenotypic character with a global coefficient of determination of 81.6%.