Estimation of outcrossing rate in a breeding population of Eucalyptus urophylla with dominant RAPD and AFLP markers

Abstract

Eucalyptus breeding is typically conducted by selection in open-pollinated progenies. As mating is controlled only on the female side of the cross, knowledge of outcrossing versus selfing rates is essential for maintaining adequate levels of genetic variability for continuous gains. Outcrossing rate in an open-pollinated breeding population of Eucalyptus urophylla was estimated by two PCR-based dominant marker technologies, RAPD and AFLP, using 11 open-pollinated progeny arrays of 24 individuals. Estimated outcrossing rates indicate predominant outcrossing and suggest maintenance of adequate genetic variability within families. The multilcous outcrossing rate (t) estimated from RAPD markers (0.93$0.027), although in the same range, was higher ('0.01) than the estimate based on AFLP (0.89$0.033). Both estimates were of similar magnitude to those estimated for natural populations using isozymes. The estimated Wright's fixation index was lower than expected based on t possibly resulting from selection against selfed seedlings when sampling plants for the study. An empirical analysis suggests that 18 is the minimum number of dominant marker loci necessary to achieve robust estimates of t. This study demonstrates the usefulness of dominant markers, both RAPD and AFLP, for estimating the outcrossing rate in breeding and natural populations of forest trees. We anticipate an increasing use of such PCR-based technologies in mating-system studies, in view of their high throughput and universality of the reagents, particularly for species where isozyme systems have not yet been optimized.

Outcrossing rate between 'Haden' and 'Tommy Atkins' mangoes estimated using microsatellite and AFLP markers

“…This model has been successfully applied by different authors (Gaiotto et al, 1997;Muluvi et al, 2004;Muchugi et al, 2008) to species without available co-dominant markers.…”

“…Dominant DNA markers, such as RAPD and AFLP, have been used to estimate outcrossing rates in Moringa oleifera (Muluvi et al, 2004) and Eucalyptus urophylla (Gaiotto et al, 1997), despite limitations on the correct genotypic identification of individuals. To overcome this limitation, Ritland (2002) developed the multilocus model to estimate outcrossing rates in plant species, so that dominant markers could be applied in mating system studies.…”

Cellulose content as a selection trait in breeding for kraft pulp yield in Eucalyptus urophylla

“…The significance of fixed effects was tested using F-tests. The outcrossing rate in natural stands of E. urophylla has been estimated to be about 90% (House and Bell, 1994;Gaioto et al, 1997). This information was incorporated in the calculations of genetic parameters in ASReml by declaring a selfing rate of 10% in the population in the model (Gilmour et al, 2006).…”

Gene flow estimation with microsatellites in a Malagasy seed orchard of Eucalyptus grandis

“…For Eucalyptus citriodora, Yeh et al (1983) reported an outcrossing rate of 85% estimated with isozymes. For Eucalyptus urophylla, Gaiotto et al (1997) estimated around 90% with RAPD and AFLP markers.…”