Abstract
Polyploidy plays an important role in crop improvement. Polyploid plants, particularly those produced through unreduced gametes (2n gametes), show increased organ size, improved buffering capacity for deleterious mutations, and enhanced heterozygosity and heterosis. Induced polyploidy has been widely used for improving floriculture crops, however, there are few reported sexual polyploid plants in the floriculture industry. This study evaluated nine cultivars of Cymbidium Swartz and discovered that 2n male gametes occurred in this important orchid. Depending on cultivars, 2n male gamete formation frequencies varied from 0.15 to 4.03%. Interspecific hybrids generally produced more 2n male gametes than traditional cultivars. To generate sexual polyploid plants, seven pairs of crosses were made, which produced five triploid and two tetraploid hybrids. Two triploid hybrids were evaluated for in vitro regeneration and growth characteristics. Compared to the diploid parents, the triploids were more easily regenerated through rhizomes or protocorms, and regenerated plants had improved survival rates after transplanting to the greenhouse. Furthermore, the sexual polyploid plants had more compact growth style, produced fragrant flowers, and demonstrated heterosis in plant growth. Through this study, a reliable protocol for selection of appropriate parents for 2n gamete production, ploidy level evaluation, in vitro culture of polyploid progenies, and development of new polyploid cultivars was established. Our study with Cymbidium suggests that the use of 2n gametes is a viable approach for improving floriculture crops.
Highlights
Cymbidium Swartz, or boat orchid, is a genus of evergreen flowering plants in the family Orchidaceae
Cymbidium is known as the King of Orchids due to its fragrant flowers and multitudes of colors which can remain in bloom for up to 3 months
Sexual polyploidization through 2n gametes can be of immense significance because it can combine genetic effects of polyploidy with meiotic recombination and sexual hybridization and produce tremendous genetic variation and heterosis (Ogburia et al, 2002; Ramanna and Jacobsen, 2003; Brownfield and Köhler, 2010; Khan et al, 2010; Lai et al, 2015)
Summary
Cymbidium Swartz, or boat orchid, is a genus of evergreen flowering plants in the family Orchidaceae. It is mainly native to China and northern Asia and is one of the most important orchids produced commercially as cut flowers and potted flowering plants around the world (Xie et al, 2017). Terrestrial Cymbidium sinense, C. ensifolium, C. faberi, C. kanran, Unreduced Gamete Formation in Cymbidium and C. goeringii are the most popular and economically significant ornamental plants in China. These species have been cultivated since the time of Confucius (551–479 BC) because of their graceful leaves, erect inflorescences, and sweet-scented flowers (Liu Y. et al, 2017). Interest in cymbidiums has shifted from cultivars with small flowers to those possessing large and round flowers with long-lasting inflorescences and fragrance and more robust stems and leaves
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