ESTIMATION OF OUTCROSSING RATE IN A BREEDING POPULATION OF EUCALYPTUS-UROPHYLLA WITH DOMINANT RAPD AND AFLP MARKERS

Eucalyptus breeding is typically conducted by selection in open-pollin ated progenies. As mating is controlled only on the female side of the cross, knowledge of outcrossing versus selling rates is essential for maintaining adequate levels of genetic variability for continuous gai ns. Outcrossing rate in an open-pollinated breeding population of Euca lyptus urophylla was estimated by two PCR-based dominant marker techno logies, RAPD and AFLP, using 11 open-pollinated progeny arrays of 24 i ndividuals. Estimated outcrossing rates indicate predominant outcrossi ng and suggest maintenance of adequate genetic variability within fami lies. The multilcous outcrossing rate (t(m)) estimated from RAPD marke rs (0.93 +/- 0.027), although in the same range, was higher (alpha > 0 .01) than the estimate based on AFLP (0.89 +/- 0.033). Both estimates were of similar magnitude to those estimated for natural populations u sing isozymes. The estimated Wright's fixation index was lower than ex pected based on t, possibly resulting from selection against selfed se edlings when sampling plants for the study. An empirical analysis sugg ests that 18 is the minimum number of dominant marker loci necessary t o achieve robust estimates of t,. This study demonstrates the usefulne ss of dominant markers, both RAPD and AFLP, for estimating the outcros sing rate in breeding and natural populations of forest trees. We anti cipate an increasing use of such PCR-based technologies in mating-syst em studies, in view of their high throughput and universality of the r eagents, particularly for species where isozyme systems have not yet b een optimized.