In vitro conservation and genetic diversity of threatened species of Melocactus (Cactaceae)
The high endemism, the natural habitat degradation, and the over-collection for ornamental purposes have led some species such as Melocactus paucispinus and Melocactus glaucescens to be threatened with extinction. The use of in vitro conservation techniques, such as slow growth storage, promotes the preservation of genetic diversity with integrity. The goal of this study was to establish a strategy for in vitro conservation of apical segments of the cladode of M. paucispinus and M. glaucescens and evaluate the genetic diversity of individuals from in vitro germinated plants. For such purpose, different concentrations of the plant regulator ancymidol and the osmotic agent sucrose on the inhibition of the in vitro growth were tested, and the genetic diversity of M. paucispinus and M. glaucescens individuals stored in vitro was evaluated. Sucrose showed higher efficiency in the reduction of growth than ancymidol for both species. However, due to the reduction in survival percentage, the use of sucrose over 75 g L−1 in the in vitro conservation of both species for 360 days is not recommended. In the genetic diversity analysis, 76.92% of polymorphic loci (P), expected heterozygosity (He) = 0.276 and Shannon index (S) = 0.414 were observed for M. paucispinus. For M. glaucescens, the observed values were P = 95.38%, He = 0.228 and S = 0.369. These values observed here were higher than those previously found for the natural populations of these species, which demonstrated that this in vitro collection showed genetic diversity and can be used in management and reintroduction programs of these species.