Avaliação da morfogênese para a conservação ex situ de cactáceas micro endêmicas da Chapada Diamantina (BA)

Abstract

Cacti have great commercial relevance, with distribution nearly restricted to the Americas, and the elevated threats of extinction of species from this botanical family raise some concerns about their conservation. Ex situ conservation techniques can promote long-term viability of explants for propagation that serves both conservation and industrial purposes, however they demand a delicate balance of techniques and a deep study regarding the species' specific morphophysiological behavior. This dissertation aims to understand the morphophysiological behavior in the regeneration of different kinds of explants from Micranthocereus flaviflorus (Buining & Brederoo) P.J. Braun & Esteves and Micranthocereus alvinii (M. Machado & Hofacker) N.P. Taylor & M. Lowry. After inducing the material, callus portions of 0.01 cm², 0.04 cm², or 0.16 cm² of both species were submitted to culture in half-strength MS, 1.5% sucrose, and pH ranging from 5.6 to 5.8, supplemented with various combinations and concentrations of the auxins 2.4-D and NAA and the cytokinins BAP and KIN, and part of the samples were dry-weighted every 15 days for a total of 90 days. All tested callus sizes were able to regenerate. The highest mean was observed for treatments containing 5 μM 2.4-D with 5 μM KIN for M. alvinii and 5 μM 2.4-D with 10 μM BAP for M. flaviflorus. There was a significant increase in dry weight from day 75, which continued until day 90 for M. flaviflorus, unlike M. alvinii. Treatments containing 5 μM 2.4-D with 10 μM KIN for M. alvinii and 5 μM 2.4-D with 10 μM BAP for M. flaviflorus fit linear equations and may extend the growth phase beyond the 90 days tested. We also tested five different explants under suitable combinations of growth regulators to induce shoot or callus formation. For M. flaviflorus, a single areole was able to regenerate, producing either shoots or calluses, while for M. alvinii, although a single areole was able to produce calluses, the smallest explant capable of producing shoots was a quarter of a transversal section with one row of areoles. For the establishment of a cell suspension, 0.16 cm² portions were inoculated in test tubes or Erlenmeyer flasks subjected to a 16 h light/day cycle or complete darkness. In all treatments, we successfully obtained cell suspensions, and there was no interference from the container type or light exposure. This study contributes to the development of basic techniques for future application of cryopreservation practices in isolated cactus tissues, aiming to assist with the ex situ conservation of species in this botanical family.