Effects of Plant Growth Promoting Rhizospheric Bacteria (PGPR) on Survival, Growth and Rooting Architecture of Eucalyptus Hybrid Clones

Clonal plantation involves the rooting of cuttings from superior genotypes selected for their hybrid vigor and desired qualities. However, the cuttings of some Eucalyptus species and their hybrid genotypes present difficulties in their rooting capacity. Applying PGPR to cutting growth medium as a root stimulating agent has not been extensively studied for Eucalyptus tree species. We aimed to assess the rooting capacity of cuttings taken from two poor-rooting Eucalyptus hybrid clones of E. grandis x E. nitens through the application of PGPR in nursery trials. Seven rhizospheric bacterial species that demonstrated the ability to produce indole-3-acetic acid and to solubilise phosphate were used to prepare two rhizospheric consortium inoculums in which Pseudomonas-Bacillus strains and non-Pseudomonas-Bacillus were grouped. Inoculums were tested for their rooting stimulating capacity on cuttings of the hybrids GN 018B and GN 010 and compared to the nursery standard indole-3-butyric acid. A total of 320 cuttings were treated. Both hybrid clones demonstrated significant (p < 0.0001) genotype differences for all three growth responses, i.e., total, root, and shoot length. Cuttings of both hybrids demonstrated high survival rates and rooting percentage. Although several rooting architectural configurations were prevalent, the Pseudomonas-Bacillus consortium promoted adventitious root development and fibrosity in GN 018B hybrids.