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In vitro regeneration systems provide a powerful tool for manipulating ploidy to facilitate breeding and development of new crops. Polyploid induction can expand breeding opportunities, assist with the development of seedless triploid cultivars, enhance ornamental characteristics and environmental tolerances, increase biomass and restore fertility in wide hybrids. In vitro ploidy manipulation is commonly induced using antimitotic agents such as colchicine, oryzalin and trifluralin, while many other antimitotic agents have been relatively unexplored. Successful induction requires a synergistic pairing of efficient penetration of the antimitotic agent and may be dependent the length of exposure and concentrations of antimitotic agents, tissue types, and interactions with basal media and plant growth regulators. In vitro conditions vary among taxa and individual genera, species, and cultivars, often requiring unique treatments to maximize polyploid induction. In some taxa, the induction of polyploidy influences in vitro growth, development, and root formation. Here we provide an overview of mitotic inhibitors and their application for in vitro ploidy manipulation for plant breeding and crop improvement.

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In vitro growth responses of Magnolia ‘Ann’ to basal salt composition, cytokinins, and phenolic binding agents were investigated in a series of experiments to refine micropropagation protocols. Murashige and Skoog (MS), half-strength MS, Woody Plant Medium (WPM), Driver and Kuniyuki (DKW), and Blaydes basal salts in conjunction with 1 g·L−1 activated charcoal (AC) or 1 g·L−1 polyvinylpyrrolidone (PVP) were evaluated as multiplication media. Benzylaminopurine (BAP), meta-topolin (mT), or 6-(γ,γ-dimethylallylamino) purine (2iP) at 2, 4, or 8 μM was investigated to optimize the cytokinin concentration. Murashige and Skoog medium supplemented with 2 μM BAP with no phenolic binding agent was an optimal multiplication medium that yielded 3.2 ± 0.2 shoots with a mean length of 17.2 ± 1.8 mm over an 8-week period. For rooting, microshoots were cultured on half-strength MS media supplemented with 0, 5, 10, or 20 μM indolebutyric acid (IBA) with or without AC. Media containing AC produced elongated microshoots suitable for rooting and ex vitro establishment. Microshoots cultured on medium supplemented with AC also had higher in vitro rooting (16%) and higher ex vitro rooting (75%) compared with those without AC regardless of in vitro IBA concentration.