Pinus rhizosphere

Loblolly pine (Pinus taeda L.) is an important tree species in Brazil, with considerable interest in genetic improvement and vegetative propagation via cuttings. However, cuttings of this species exhibit low rooting rates, limiting the use of selected clones. Plant growth-promoting bacteria (PGPB) could be a strategy for increasing rooting efficiency in cuttings. Therefore, the aim of this study was to assess the bacterial diversity associated with the rhizosphere of loblolly pine in a commercial nursery and to select plant growth-promoting isolates to improve rooting. Analyses via 16S rRNA gene metabarcoding were conducted to compare rhizosphere and substrate samples from different loblolly pine genotypes. Additionally, rhizospheric bacteria were isolated and characterized. The selected isolates were inoculated into bean plants and loblolly pine cuttings. Metabarcoding and culturomics approaches revealed high microbial diversity. Thirty-three bacterial genera were isolated, notably Novosphingobium and Pseudomonas, and functional screening revealed growth-promoting activities, including 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and indole compounds production. Inoculation tests on bean plants revealed enhanced root growth. In loblolly pine mini-cuttings, isolate CNPF 363 (Mesorhizobium sp.) achieved up to 92.1% rooting, whereas isolate CNPF 448 (Brucella sp.) presented consistent performance across the two trials, with an average rooting rate of 83.8%. These results demonstrate the potential of PGPB derived from selected loblolly pine genotypes to improve rooting efficiency in clonal propagation through mini-cutting.