Abstract
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.
Highlights
Cactaceae family is subject to intense extractive exploitation due to its great diversity and value, mainly in the ornamental trade, which is the reason why it is considered one the most endangered groups of plants (Goettsch et al 2015; Pérez-Molphe-Balch et al 2015)
For M. glaucescens, the P values observed are similar to the results found in a study of genetic characterization of the O. ficus-indica germplasm stored in field at the University of Catania-Italy using microsatellite markers (92.8%) (Caruso et al 2010), and in a study of pitaya species (Hylocereus and Selenicereus) stored in field at Embrapa Cerrados-Brazil (95.06%) (Junqueira et al 2010)
The ancymidol or sucrose effects promoted the survival of the apical segment of cladodes, 100 and 97%, respectively, of Melocactus paucispinus and M. glaucescens plants survived 360 days after inoculation (Fig. 1c; d)
Summary
Cactaceae family is subject to intense extractive exploitation due to its great diversity and value, mainly in the ornamental trade, which is the reason why it is considered one the most endangered groups of plants (Goettsch et al 2015; Pérez-Molphe-Balch et al 2015). A progressive reduction in the size of M. paucispinus and M. glaucescens populations has been observed, caused by frequent changes in their natural habitat as well as illegal harvesting for commercial and ornamental purposes (Lambert et al 2006a; b) Due to these reasons, both species have been listed as endangered in the IUCN Red List of Threatened Species (IUCN 2020). Ex situ conservation techniques are important to preserve the genetic diversity from plant genetic resources with as much integrity as possible (Villalobos et al 1991; Rao and Hodgkin 2002; Volis and Blecher 2010) In this context, the tissue culture technique represents an efficient method for ex situ genetic diversity conservation, allowing the reduction of space for the species maintenance and promoting high multiplication rates regardless of climatic conditions (Villalobos et al 1991; Engelmann 2011). This technique is indicated for species such as M. paucispinus and M. glaucescens, whose seeds lose viability when stored for long periods (data not published)
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