Understanding the in vitro growth dynamics of Melocactus (Cactaceae) species for effective medium-term conservation strategies
摘要
Melocactus glaucescens and M. paucispinus, both endemic to Brazil, are threatened with extinction, necessitating urgent conservation strategies. Slow growth tissue culture offers a medium-term approach for conservation genetic diversity with integrity while allowing immediate use of conserved cultures in reintroduction programs when required. This study aimed to understand the effects of osmotically active substances - sucrose, sorbitol, and mannitol - on the in vitro growth dynamics of M. glaucescens and M. paucispinus shoots over 360 days to establish optimal medium-term conservation strategies. Shoots (5–10 mm) of both species were inoculated in MS culture medium gelled with 6.5 g L−1 of agar, supplemented with either 30 g L−1 sucrose (control) or varying concentrations of sucrose (45, 60, 75, 90, or 105 g L−1). Additionally, treatments included 30 g L−1 of sucrose combined with sorbitol or mannitol at 15, 30, 45, or 60 g L−1. Growth parameters evaluated included survival, length of the aerial portion (LAP), stem coloration (COLOR), and development of apical spines (DAS) at 120 and 360 days of cultivation. Total dry matter (TDM) of the shoots was also assessed after 360 days. After 120 days of cultivation, all cultures exhibited 100% survival. A progressive reduction in LAP and TDM was observed at higher concentrations of sucrose, sorbitol, and mannitol after 120 and 360 days of culture. COLOR shifted from medium- to reddish-green in cultures with highest concentrations of sucrose and sorbitol. Sorbitol and mannitol appeared to interact with sucrose metabolism through osmoprotective mechanisms, indicating more complex connections in the metabolism of Melocactus. Further studies are needed to clarify their roles. Based on these findings, M. glaucescens and M. paucispinus shoots can be effectively conserved in vitro in MS medium containing 75 g L−1 and 90 g L−1 sucrose, respectively. This concentration supports minimal growth without inducing stress-related changes, ensuring shoot viability for at least 360 days.