In vitro propagation of Cymbidium goeringii Reichenbach fil. through direct adventitious shoot regeneration

A chromosome-scale genome assembly and annotation of the spring orchid (Cymbidium goeringii)

Cymbidium goeringii, commonly known as the spring orchid, has long been favoured for horticultural purposes in Asian countries. It is a popular orchid with much demand for improvement and development for its valuable varieties. Until now, its reference genome has not been published despite its popularity and conservation efforts. Here, we report the de novo assembly of the C. goeringii genome, which is the largest among the orchids published to date, using a strategy that combines short- and long-read sequencing and chromosome conformation capture (Hi-C) information. The total length of all scaffolds is 3.99 Gb, with an N50 scaffold size of 178.2 Mb. A total of 29,556 protein-coding genes were annotated and 3.55 Gb (88.87% of genome) repetitive sequences were identified. We constructed pseudomolecular chromosomes using Hi-C, incorporating 89.4% of the scaffolds in 20 chromosomes. We identified 220 expanded and 106 contracted genes families in C. goeringii after divergence from its close relative. We also identified new gene families, resistance gene analogues and changes within the MADS-box genes, which control a diverse set of developmental processes during orchid evolution. Our high quality chromosomal-level assembly of C. goeringii can provide a platform for elucidating the genomic evolution of orchids, mining functional genes for agronomic traits and for developing molecular markers for accelerated breeding as well as accelerating conservation efforts.

Complete chloroplast genome sequence of an orchid hybrid Cymbidium sinense (♀) × C. goeringii (♂)

The complete chloroplast genome sequence of the Cymbidium hybrid, C. sinense (♀) × C. goeringii (♂) was assembled in this study. The circular genome was 150,149 bp in length with an overall GC content of 37.1% and consisted of a pair of 25,691 bp inverted repeats, and two single-copy regions that were 84,987 bp and 13,780 bp, respectively. Gene annotation analysis identified 109 genes including 75 protein-coding genes, 30 transfer RNA, and 4 ribosomal RNA genes. Phylogenetic analysis showed its closest relationship to Cymbidium sinense, reflecting a maternal inheritance of chloroplasts.

In Vitro Propagation of Gastrochilus matsuran (Makino) Schltr., an Endangered Epiphytic Orchid

Gastrochilus matsuran (Makino) Schltr. (Orchidaceae) populations are declining quickly because of overexploitation, climatic changes, and deforestation; therefore, mass-production protocols are required for this orchid. Natural propagation of this species is often hampered by meager seed germination and slow growth. Thus, our aim was to establish an effective protocol for the in vitro propagation of G. matsuran and reduce the risk of its extinction. We investigated the impacts of culture media, coconut water (CW), and plant hormones (gibberellic acid (GA₃), indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), α-naphthaleneacetic acid (NAA), and thidiazuron (TDZ)) on asymbiotic germination, multiplication and conversion of protocorms, and plantlet development. Maximal seed germination (93.3%) was achieved on ½ MS medium without vitamins plus 5% CW, 1 µM NAA, and 1.5 µM GA₃. Secondary protocorm formation was best achieved on ½ MS medium without vitamins plus 2 µM TDZ. The conversion of protocorms into seedlings was maximized by supplementation with 2 µM IBA or 1 µM NAA. Acclimatized plantlets that exhibited exuberant growth on sphagnum moss were reintroduced to tree trunks in a natural habitat, with a 67% survival rate. This in vitro propagation procedure would be helpful for the mass production and conservation of this rare epiphytic orchid.