Investigating the origin and genetic diversity of improved Eucalyptus grandis populations in Brazil

Abstract

To better understand the genetic variability among and within Eucalyptus grandis populations introduced in Brazil, we use microsatellite loci to investigate the mating system, genetic structure, and Australian origins of several introduced provenances. Our sample includes 981 trees from ten Brazilian populations and 254 trees from 18 Australian populations. Significant higher observed heterozygosity (Ho) and significant lower fixation index (F) was detected in grouped Brazilian provenance (Ho = 0.753, F = 0.140) than in Australian samples (Ho = 0.680, F = 0.220). However, Brazilian samples presented significantly lower genetic differentiation (GST ′) among populations (0.541) than Australian populations (0.838) indicating that the overall genetic diversity captured in the Brazilian collection is low due to the limited number of populations represented. All sampled Brazilian populations showed 100% correct expectation of attribution to their reference population, showing consistency with historical information. A lower fixation index (F) was detected in Brazilian seed trees (−0.101) than their offspring (0.140), suggesting selection against inbred individuals between seedling and adult stages. The outcrossing rate (tm) was high (0.994) with low variability among populations (0.921–0.969). However, some mating occurred between related trees (tm-ts = 0.149) and were correlated (rp(m) = 0.113), indicating that some offspring are inbred and families are composed of different levels of relatedness. The coancestry (Θ = 0.141) was higher and the effective size within families (Ne = 3.09) lower than that expected for half-sib families (Θ = 0.125; Ne = 4). Brazilian E. grandis populations offer the possibility to develop new breeding populations with high genetic variability due to their differing origins combined with individual selection.