Propagação vegetativa de Croton urucurana Baill. (Euphorbiaceae)

Abstract

Croton urucurana Baill. is an arboreal plant from the Brazilian flora, which has great potential for forest restoration, in addition to being frequently used in folk or traditional medicine by traditional communities. However, little information about vegetative propagation is found in the literature for this species. This paper consisted of three vegetative propagation experiments, one for cutting and two for mini-cutting. Experiment I was carried out with apical cuttings of herbaceous to semi-hardwood consistency, collected periodically at the four seasons of the year (November/2017, February, May, and August/2018), applying different concentrations of indole butyric acid (IBA) in hydroalcoholic solution (50v/v). The cuttings collection time has not influenced the percentage of rooted and non-rooted cuttings, whose averages were 28.6% and 71.4%, respectively; however, it had influenced the average number of roots/cutting, average root length, and average dry mass of roots/cuttings. The IBA application influenced the average number of roots/cuttings and the dry mass of roots/cuttings positively; the concentration of 8,000 mg L-1 was the most effective. Experiment II was carried out with ministumps of seminal origin, grown in a clonal minigarden in a semi-hydroponic system, and apical mini-cuttings of herbaceous consistency, collected simultaneously with Experiment I, using different IBA concentrations in hydroalcoholic solution (50v/v). The ministumps showed survival above 90% at the end of one year of evaluation. The average production was 741 shoots per season, with annual productivity of 3.8 shoots per ministumps/season. Spring was the most favorable season of the year for the C. urucurana mini-cuttings rooting (92.7%); and summer was the least favorable season (77.2%), with 86% overall average of adventitious rooting, regardless of the season. Indole butyric acid (IBA) treatment increased the number and the dry mass of roots/mini-cuttings. Experiment III was carried out with apical mini-cuttings of herbaceous consistency, collected in December 2017, with two lengths (5 cm and 10 cm) with apex and no apex, and no IBA application. There was a significant interaction among the factors regarding the root average number per mini-cuttings, whose absence of apex has influenced the 5 cm mini-cuttings (18.4 roots/mini-cuttings), negatively, in relation to the other combinations (24.7; 27.9; and 30.6 roots/mini-cuttings). In general, it is concluded that C. urucurana can be propagated vegetatively by cuttings at any time of the year, but with a low rooting percentage, and autumn is the least promising season for root quality. The exogenous IBA application provides improvements in the quality of the formed roots. C. urucurana ministumps have high survival potential and vegetative regeneration capacity in a clonal mini-garden, with feasibility for successive collections of young shoots, regardless of the year season. The rooting of C. urucurana minicuttings was higher when they were collected in the spring and in the winter, and rooting was lower in the summer collection. The best radial quality was obtained in the spring. The exogenous IBA application increased the number and the dry mass of C. urucurana roots/mini-cuttings. The apex length and its presence or absence do not affect the rooting percentage of C. urucurana mini-cuttings. However, smaller minicuttings without apex produce fewer root.