Inbreeding in Eucalyptus Seeds

Breeding strategies have mainly relied on crosses among hybrid genotypes, resulting in the recurrent selection of a limited number of superior clones. The development of inbred lines represents a complementary approach for broadening breeding schemes and enhancing genetic control. However, obtaining self-fertilized seeds in predominantly allogamous species is laborious, costly, and technically demanding. This study evaluated whether seed morphological screening, combined with seed collection from the central areas of monoclonal stands, could improve germination efficiency, seedling uniformity, and the identification of selfed individuals. Seeds from four commercial Eucalyptus “urograndis” clones were collected from the center of monoclonal plantations. Seed screening was conducted using granulometric sieves, manual selection based on physical integrity, and separation by weight using a seed blower, generating distinct morphological categories. Germination rate, seedling height at three months after germination, and genetic parameters were evaluated using 16 SSR markers, including selfing rate, heterozygosity, and inbreeding coefficient. Germination rates was differed among clones and morphological categories, with consistently higher values observed for heavier seeds and larger diameter classes. Seed screening increased overall germination efficiency and promoted greater seedling uniformity. Substantial variation in selfing rates was detected among clones, while morphological categories showed limited ability to discriminate selfed individuals, except in one clone. Seedling height was influenced by seed morphology, whereas genetic effects associated with inbreeding were significant in only one progeny. Overall, seed morphological screening represents a practical strategy to enhance seminal seedling production and reduce operational costs, supporting breeding programs and genetic diversification in commercial Eucalyptus plantations.