Indole acetic-producing bacteria promote the root development of Acacia mearnsii cuttings

Abstract

ABSTRACT Black wattle (Acacia mearnsii) is one of the most important commercial tree species in southern Brazil, where it is planted for multiple uses, such as cellulose pulp production and tannin extraction. Recently, forest companies have been directing their efforts towards vegetative propagation to improve the productivity of black-wattle plantations. However, rooting rates of this species are low, even when treated with the synthetic auxin indole-3-butyric acid (IBA). Thus, rooting black-wattle cuttings is still considered a bottleneck for industry development. On the other hand, it is known that inoculating cuttings with indole acetic acid (IAA)-producing bacteria can be an efficient method for increasing vegetative propagation. This study investigated the potential of two bacterial strains to promote root development in black wattle. The strains SEMIA 436 and 439 (Agrobacterium radiobacter), previously isolated from the common bean and detected as high-IAA producers, were also evaluated in relation to their colonisation capacity in seedling roots. Results showed that inoculation with both strains increased rooting rates by 20−30% compared with non-treated and IBA-treated cuttings. Moreover, inoculation increased root dry mass, length and volume. Strain SEMIA 436 demonstrated higher colonisation capacity.