Plant growth-promoting rhizobacteria enhance adventitious rooting of mini-cuttings from Ilex paraguariensis clones

Abstract Key Message Plant-growth-promoting rhizobacteria increase adventitious rooting in yerba mate mini-cuttings, particularly in low-rooting genotypes; these bacteria showed potential to improve clonal propagation efficiency. Abstract Yerba mate ( Ilex paraguariensis A. St.-Hil.) is a forest species of great economic, social, and ecological importance in South America. However, clonal propagation via mini-cuttings remains limited due to low rooting rates. This study aimed to investigate the bacterial community associated with yerba mate clones and to identify plant growth-promoting rhizobacteria (PGPR) capable of inducing adventitious rooting in mini-cuttings. Bacterial isolates were obtained from clones with high rooting capacity and were characterized and identified through partial 16S rRNA gene sequencing. In parallel, the bacterial community associated with clones exhibiting contrasting rooting capacities was assessed. A total of 87 bacterial isolates were obtained, of which 15 were selected and belonged to different PGPR-associated genera. No significant differences in bacterial diversity were observed among clones, and the phyla Proteobacteria and Actinobacteriota were the most abundant. Inoculation assays were conducted using bacteria isolated from yerba mate and from other species. Bacterial inoculation positively affected rooting rate and root dry mass. In the high-rooting clones, isolate ERR 1227 increased the rooting rate to 85%; however, this value was not significantly different from the 60% observed in the non-inoculated control. In the low-rooting clones, isolate CNPF 715 achieved a rooting rate of 35%, which was higher than the 18.3% observed in the non-inoculated control. Isolate CNPF 363 exhibited consistent results across both groups (71.7% high and 31.7% low-rooting clones). These findings demonstrate that selected rhizobacteria can enhance adventitious rooting, particularly in low-rooting genotypes, highlighting PGPR as a promising tool for improving yerba mate clonal propagation.