7.1.5. *Cymbidium* Cultivar Sunny Bell

A *Cymbidium* variety Sunny Bell (*C. karan* x *C. eburneum*) was developed at the National Institute of Horticultural & Herbal Science, Rural Development Administration, Suwon, Korea in 2013 [39]. Monoterpenes, sesquiterpenes, and aliphatics have been recognized as the major volatile compounds in *Cymbidium* Sunny Bell [39]. Twenty-four volatile components were identified in the Sunny Bell flowers; among the total volatiles, petals produced dominant volatile compounds compared to other floral tissues such as sepal, labellum, and column. Linalool is the major compound responsible for the floral volatile profile in Sunny Bell.

Some species in the genus *Cymbidium*, including *C. floribundum*, *C. pumilum*, and *C. suavissimum*, release identical volatiles for pollinator attraction. Various types of alkenes, esters, and fatty acid derivative compounds are released for pollinator attraction. It has been reported that *Cymbidium* flowers are rich in volatile compounds including cineole, isoeugenol, and (-) selinene [104]. Floral scent and color are major traits for floriculture crops in developing new cultivars of *Cymbidium*. Furthermore, 21–28 floral scent compounds have been identified as major volatile components in the flowers of three *Cymbidium* varieties [105]. The volatiles mainly comprise monoterpenes, aliphatics, and sesquiterpenes, and their content values have exceeded 90% [105]. Their aromatic characteristics can be determined by the profiles of each VOC that may vary depending on each genotype [105].

### **8. Final Remarks and Future Directions for Overcome the Challenges**

At present, orchid industries worldwide are facing various difficulties. For developing new cultivars, physiological and genomic maps have been needed to produce markers. RNA-illumina sequencing technology has been extensively used for identifying gene expression at a genome-wide scale in many organisms, including non-model plants. The adoption of this technique, especially mRNA sequencing from floral tissues and de novo transcriptome construction (Figure 4), has been performed in several orchid species, with a goal of identifying genes involved in the biosynthesis and/or biosynthetic pathways of floral volatiles [28,110].

**Figure 4.** Schematic representation of functional studies for orchid breeding to develop floral scent trait.

Moreover, other strategies include molecular evolutionary analysis tools. For example, testing for gene duplication and selection signatures in hypothesized pathway genes, from a phylogenetic perspective, is frequently used. For the identification of significant candidate genes and pathways, targeted and strategic transcriptome analyses of fragrant and non-fragrant flower organs and tissues are often the first key step. Regulation of DEGs between fragrant and non-fragrant tissues and developmental stages can be investigated. The latter provides a key baseline for identifying DEGs in fragrant tissues. This approach was utilized for the breakthrough discovery on volatile biosynthesis [58,111] and may hold potential for elucidating other biosynthetic pathways. RNA-sequencing analysis across species, with the goal of identifying shared gene expression and metabolic pathways, may also prove informative. Transformation technology has been developed for orchids; a few successful methods using virus induced gene-silencing (VIGS) approaches have recently been demonstrated as efficient strategies for functional studies of genes in orchids (Figure 4). Furthermore, transgenic approaches, such as the overexpression of floral scent genes and/or genome editing, have also been recently developed for orchids.
