Acacia mearnsii pyroligneous acid as a promoter of rooting and quality of rooted cuttings of subtropical Eucalyptus

The pyroligneous acid of Acacia mearnsii enhanced the rooting, promoted higher carbon allocation and quality of rooted cuttings representing a novel, natural input for subtropical Eucalyptus clone production.

The development of strategies aimed at optimizing the clonal propagation of Eucalyptus species, especially those that are difficult to root, is of great importance. In this context, the present study aimed to evaluate the effect of applying different concentrations of the pyroligneous acid (PA) of Acacia mearnsii De Wild, through foliar spraying, on mini-cuttings of E. benthamii, E. dunnii, and the hybrid, E. urophylla × E. dunnii, during the summer and winter periods in southern Brazil. The experiments were carried out in a greenhouse in a factorial scheme, testing four PA concentrations (0 [control], 2%, 4%, and 6%) and five clones, E. benthamii (B1 and B2), E. dunnii (D1 and D2), and E. urophylla × E. dunnii (UD). Thirty days after staking, the percentage survival of the mini-cuttings was evaluated, and at 50 days, adventitious rooting and callogenesis, as well as the morphological attributes of the mini-cuttings were evaluated. Chemical analysis of the PA revealed the presence of phenolic compounds, primarily syringol, pyrocatechol, and guaiacol derivatives. The PA of A. mearnsii was shown to be a potential alternative input for maximizing the rooting percentages of subtropical Eucalyptus clones that are difficult to propagate. PA contributed to greater allocation of dry matter and quality (Dickson Quality Index) of clonal seedlings, except for clone D2. Spraying concentrations between 2 and 4% PA, applied twice a week, optimized the subtropical eucalyptus mini-cuttings, with the dose of maximum technical efficiency being (DMTE) estimated between 3.5 and 4.5% PA. PA represents a novel, natural input for the production of clones of E. benthamii, E. dunnii, and the hybrid, E. urophylla × E. dunnii.