Even cyclamens grown from the same pair of parents do not release identical blends of floral scent compounds. One individual may contain more citronellol, while another has a higher proportion of nerol. A 2018 study demonstrated these differences by examining the diversity of scents in wild species and analyzing flowers produced through actual crosses.
The goal was not merely to find fragrant cyclamens, but to create a range of choices in scent, as in flower color and shape. The researchers therefore addressed two questions: which wild species might serve as parents, and how parental scents appear in their offspring.
Collecting scents from 17 wild Cyclamen species
At the time, fragrant interspecific cyclamens had been produced by crossing Cyclamen persicum, the source species of cultivated varieties, with the wild species Cyclamen purpurascens. Suspecting that other wild species might also offer breeding material, the researchers examined 17 species.
Flowers on potted plants were enclosed in bags, and emitted compounds were collected on an adsorbent over 24 hours while air flowed through. The samples were then examined by gas chromatography and mass spectrometry. Different sample-introduction methods were used for the nine strongly scented and eight weakly scented species. The compounds’ odor qualities were classified using a Takasago fragrance database.
Characteristic scent compositions were reported for 14 species. The remaining three, C. coum, C. parviflorum, and C. balearicum, had very weak scents and yielded too little material for inclusion in the detailed table, although traces of some scent compounds were detected.
From hyacinth-like notes to fruit and coconut
The wild species did not all smell alike. C. cilicium and C. alpinum had hyacinth-like notes, with phenylacetaldehyde among their major constituents. C. cyprium and C. pseudibericum were described as having lemon- or lily-of-the-valley-like notes, and compounds including geraniol and geranyl acetone were found.
C. mirabile, meanwhile, had fruity and coconut-like notes. In addition to fruity butyl acetate, a type of lactone with a coconut-like odor was detected. These differences suggest that breeding could target fruity scents as well as floral notes reminiscent of rose or hyacinth.
Among the wild species examined, C. purpurascens had the highest reported number of compounds, at 62. Alongside floral compounds such as citronellol, it contained fruity compounds and was used as a parent in the subsequent crossing experiments.
The compound proportions reported in the paper are ratios of analytical peak areas. A proportion twice as large, for example, does not mean that people perceive twice as much scent. Some compounds are readily perceived at low levels, and combinations of compounds influence the overall aroma.
Even flowers from the same parents have different blends
Before making the crosses, the researchers examined 18 individuals representing 11 cultivated varieties and eight C. purpurascens individuals, confirming variation in composition within species and cultivars. They then crossed the cultivar Akebono with C. purpurascens individual 40-3 and raised six offspring. A second cross, between Schubert and C. purpurascens individual 40-2, produced five offspring. The method involved culturing ovules obtained from crosses between different species.
The six Akebono-derived offspring differed in the proportions of citronellol, nerol, and geraniol, which contribute rose-like notes. Among these three compounds, citronellol was most abundant in individual 1; nerol and citronellol stood out in individual 2; and all three occurred in relatively similar proportions in individual 3. Even with the same parental pairing, offspring compositions offered a range from which to select.
Citronellol predominated in many Schubert-derived offspring, but there was also an exception in which geraniol was a major constituent. However, the two crosses differed not only in the maternal cultivar but also in the paternal wild individual. The design did not isolate the mother alone as the cause of differences between the groups.
Some compounds were inherited, while others newly appeared
The complete set of compounds was not simply transferred unchanged from parents to offspring. Methyl citronellate, which was not detected in the cultivated varieties examined, was found in three Akebono-derived and three Schubert-derived individuals. Floral compounds present in the wild species, including farnesols, also appeared in the offspring.
Furthermore, benzyl acetate was found in some Akebono-derived offspring and benzyl alcohol in some Schubert-derived offspring, although neither had been detected in the respective parents used in the crosses. Conversely, methyl benzoate, which had been expected to provide a fruity note, was not detected in these hybrids.
The authors suggested that the inheritance of scent compounds involves multiple biosynthetic pathways and enzyme activities and is difficult to explain through simple inheritance. The study did not directly investigate the genetic mechanisms; instead, chemical analysis pointed to possibilities to test in future breeding work.
Summary
Wild Cyclamen species showed diverse combinations of scent compounds, ranging from hyacinth-like floral notes to fruity and coconut-like notes. Even hybrid individuals from the same parents differed in their proportions of citronellol, nerol, geraniol, and other compounds, and in some cases contained substances not detected in either parent.
Challenges remain in introducing a desired scent, as illustrated by the absence of the expected methyl benzoate in the offspring. The study shows that breeding floral fragrance requires both selecting parental species and examining the resulting individuals one by one.
The paper lists one author as affiliated with Takasago International Corporation at the time of the research and acknowledges researchers from that company. No separate research-funding or conflict-of-interest declaration section could be found.
Reference
Shibusawa, N., Nohara, I., & Ohsawa, R. (2018). Interspecific variation of scent characteristics in the Cyclamen genus and the utility of the variation. Horticultural Science, 45(4), 193–204. doi:10.17221/111/2017-HORTSCI (Full original paper)
