Enhancing Eucalyptus seedling quality through multi-strain bacterial inoculation.

The use of bacterial inoculants in forestry is a promising strategy to enhance seedling quality, reduce costs, and promote sustainable cultivation. This study evaluates the effects of a multi-strain bacterial consortium on Eucalyptus seedlings, considering the plant growth, microbial community composition, and seedling quality. A consortium consisting of one representative from each of five bacterial genera - Bacillus, Paenibacillus, Paraburkholderia, Methylobacterium, and Mesorhizobium - was applied to three Eucalyptus clones, a large field experiment was conducted in a tree nursery. To assess the root endophytic community composition, samples were processed and analyzed using 16 S rRNA metabarcoding sequencing to characterize the bacterial communities present. After 13 weeks, we assessed microbial diversity, morphological seedling traits, and survival rates. While inoculation did not significantly affect bacterial richness and diversity, it altered the root microbial community structure. Two genotypes exhibited improved seedling quality, with a higher proportion classified into superior categories, and one genotype showed a significant reduction in mortality (from 21.8% to 6.7%). Additionally, inoculated seedlings displayed reduced relative abundance of Ralstonia, a genus that includes vascular phytopathogenic species responsible for Eucalyptus wilt disease. Biomass allocation patterns varied, indicating genotype-specific responses to inoculation. These findings underscore the potential of bacterial consortia to enhance Eucalyptus seedling resilience and productivity, presenting a sustainable alternative to conventional forestry practices.