Polyploidy occurs naturally in plants through cell division errors or can artificially be induced by antimitotic agents and has ecological effects on species adaptation, evolution, and development. In agriculture, polyploidy provides economically improved cultivars. Furthermore, the artificial induction of polyploids increases the frequency; thus, it accelerates obtaining polyploid plants used in breeding programs. This is the reason for its use in developing many crops of economic interest, as is the case of orchids in the flower market. Polyploidy in ornamental plants is mainly associated with flowers of larger size, fragrance, and more intense coloring when compared to naturally diploid plants. Currently, orchids represent the largest flower market worldwide; thus, breeding programs aim to obtain flowers with the larger size, durability, intense colors, and resistance to pathogens. Furthermore, orchid hybridization with polyploidy induction has been used to produce improved hybrid cultivars. Thus, the objective of this review was to compile information regarding the natural occurrence, importance, and methods of induction of polyploidy in orchids. The study also summarizes the significance of polyploids and techniques associated with artificially inducing polyploidy in different orchids of commercial relevance.

The Cattleya (Orchidaceae–Laeliinae subtribe) intergeneric hybrids, such as Brassolaeliocattleya (Blc.), have great ornamental value, due to their compact-size, with large and high color diversity of flowers. Artificial induction of polyploidy brings agronomic, ornamental and genetic benefits to plants. Polyploidization efficiency depends on factors, such as the type of antimitotic, polyploidization method, concentrations, exposure times and type of explant. This study aimed to develop a protocol to polyploidize Blc. orchids, by testing two types of explants (seeds and protocorms), concentrations and exposure times to colchicine. The effects of colchicine on the in vitro development of explants were also investigated. The responses of explants to colchicine depended on the concentrations, exposure time and the interaction of these factors. Flow cytometric analysis evidenced high endopolyploidy and allowed the separation of polyploidized (4C, 8C and 16C peaks) from non-polyploidized (only 2C and 4C peaks) plants. The highest percentage of polyploid plants was regenerated from protocorms (16.4%) treated with colchicine instead of seeds (3.2%). Protocorms treated with colchicine at 500–750 μM for 18 h resulted in the best percentage of polyploidization. Additionally, in vitro natural polyploidization using protocorms was reported (11.5%). Cytological analyses allowed an estimation of the number of chromosomes of the parents (≡70), polyploidized (≡140) and non-polyploidized progeny (≡70).

No abstract