Unraveling the inbreeding depression patterns in a self-pollinated eucalyptus population

Abstract Genetic improvement greatly contributed to the success of the forest industry in Brazil. While past selection efforts in Eucalyptus spp. have yielded satisfactory genetic gains, the response to selection in the last decade has fallen below expectations. Recent research suggests that inbreeding-based selection strategies, well-established in crops such as rice and maize, could be adapted to enhance perennial species such as guava and can be expanded to forest species, such as eucalypt. In this context, 20 elite Eucalyptus spp. genotypes were self-pollinated, producing 30 progenies per family. A total of 600 individuals were planted in an experimental trial and evaluated for growth traits at 3 years of age. Both the progeny and the 20 parent geno-types were genotyped using SNP chips. This research aims to unravel the patterns of inbreeding depression in this S0:1 population of Eucalyptus spp., by examining autozygosity and genomic inbreeding patterns, estimating in-breeding depression (ID) and genetic parameters, and studying the impact of the unbalance between selfed and crossed individuals on the inbreeding depression estimator. The results revealed that dominance variance accounted for a notable portion of the phenotypic variation, demonstrating the significance of non-additive genetic effects in diameter at breast height (DBH). ID was evident, with reductions in DBH observed in most families as ho- mozygosity increased. Simulations highlighted that unbalanced sample sizes of selfed and crossbred individuals could bias estimates of ID. By integrating genomic data and advanced quantitative methods, this study brings new information into the genetic consequences of self-pollination in eucalyptus, offering a foundation for managing inbreeding and enhancing genetic gains in perennial breeding. Competing Interest Statement The authors have declared no competing interest.