Root-enhancing properties of rhizospheric bacteria on Eucalyptus hybrid cuttings

Published Thesis ; Worldwide, the demand for hardwood from commercial plantations is rising as the consumption of forest products increases. In Eucalyptus plantation forestry the formation of interspecific hybrids has driven the commercial forestry industry to produce a variety of different hybrids that are often deployed in marginal areas. Superior hybrid genotypes are deployed through the application of vegetative propagation and the rooting of cuttings. However, the cuttings of some hybrid genotypes demonstrate relatively low rooting percentages, which results in financial losses experienced by many commercial forestry nurseries. This study was thus undertaken to assess the potential of rhizospheric bacteria to improve the rooting capacity of two hybrids clones of E. grandis × E. nitens (GN 018B and GN 010). Methods: Firstly, the rhizospheric bacterial composition of Eucalyptus rhizospheric soils of different ages were characterised using fatty acid methyl ester (FAMEs) analyses. Thereafter, rhizospheric bacteria were isolated from Eucalyptus rhizospheres and characterised by sequencing the ≈1,300 base pair fragment of the 16S rRNA gene, after which the sequences were submitted to BLAST searches to identify the bacterial strains. Thereafter, the identified bacterial strains were tested for two important root promoting characteristics; the ability to produce indole-3-acetic acid and to solubilise phosphates. Bacterial inoculums were prepared and tested on cuttings of the two hybrids in the nursery. Four treatments were applied to the cuttings; the nursery standard, which acted as the control, two treatments prepared from the isolated rhizospheric bacteria and a commercial treatment containing a live fungus. Cutting survival, rooting, rooting architecture and growth were measured after eight weeks of growth. Results: This study revealed that rhizospheric microbial communities’ diversity evolved over time. Younger rhizospheres displayed significantly greater diversity when compared to the older rhizospheres. The ...