Physiological and anatomical aspects of the rooting of Brunfelsia pauciflora cuttings

Brunfelsia is an important genus of the Solanaceae family due to its ornamental aspects and pharmacological properties. Brunfelsia pauciflora stem cuttings represent an alternative to seedling production for its propagation. There is no scientific data currently available concerning B. pauciflora cuttings, although previous studies with Brunfelsia uniflora indicated that it may be difficult to root. Anatomical barriers have been reported as limiting factors for some species that are difficult to root. We investigated the effects of the plant growth regulator indolebutyric acid (IBA) and the influence of the seasons of the year on the rooting of B. pauciflora stem cuttings and compared its rooting to B. uniflora. We also investigated the possible influence of anatomical barriers and starch contents on their rooting. Cuttings of B. pauciflora (7 ± 1 cm long) were made in the autumn of 2019, spring/2019, and summer/2020, and treated with IBA at concentrations of 0, 2000, 4000, and 8000 mg L⁻¹. For comparison, similar cuttings of B. uniflora were prepared during spring/2019 and treated with IBA concentrations of 0, 4000, and 8000 mg L⁻¹. The rooting variables of both species were analyzed after 120 days of growth in a greenhouse. For the anatomical analyses, segments of the base of the cuttings were collected on the day of their collection, and again after the 120 day growth period. The samples were embedded in historesin, sectioned, and stained with toluidine blue and Lugol's iodine solution. No combined influence of plant growth regulator concentrations and the season of the year was identified, indicating that those factors act separately on the adventitious rooting of B. pauciflora. The IBA plant growth regulator did not significantly affect any of the variables analyzed. The greatest rooting of B. pauciflora (38.8%), the highest leaf maintenance (82.0%), and the lowest mortality rate (11.2%) were observed in the summer. The species can be classified as difficult-to-root. B. uniflora, on the other hand, evidenced a greater rooting capacity (52.2%) in the spring than B. pauciflora (12.2%). The use of IBA (4000 mg L⁻¹) resulted in an increased rooting rate of B. uniflora. Anatomically, it was possible to identify the origin of the root primordia as the vascular cambium region, with root formation being defined as direct. A ring of perivascular fibers, often indicated in the literature as an anatomical barrier, was not observed as such in B. pauciflora, as rooting not only overcame the fibers, but also the callus mass. The two species of Brunfelsia differed in terms of their starch contents, which was greater in B. uniflora and appeared to favor its rooting.