EVALUATING POPULATION STRUCTURE BY NEUTRAL MARKERS AND QUANTITATIVE GENETIC PARAMETERS IN A THINNED PROGENY TRIAL OF EUCALYPTUS UROPHYLLA

The aim of this study was to estimate from microsatellite variation the levels of homozygote excess within nine populations comprising a combined population and progeny trial of Eucalyptus urophylla in northern Vietnam and to compare the population differentiation estimated by molecular markers with that estimated from growth traits. The material was thinned in year 2 (removing 75% of the trees) and year 5 (removing 37% of the remaining trees). Microsatellite variation was measured after the second thinning. Homozygote excess (F-IS) among populations ranged from 0.069 to 0.198. Most of the molecular variation was within populations (97.1% of the total variation), in agreement with the low FST value (0.023) of neutral molecular markers (F-ST) (0.023). Estimates of quantitative trait differentiation (Q(ST)) based on a univariate model among populations for height and diameter at breast height were low over the first eight years of the trial, at most 0.21. This presumably reflected selection for the same traits in a common environment. The differences between Q(ST) after the second thinning and F-ST, a measure of the effects of selection, were also small. Prospects for further breeding progress are bright, whether or not crosses are made among populations.