Handbook of Vanilla Science and Technology

Fig. 14.2 Phylogenetic relationshipsamong selectspecies of Vanilla. Thecladogramis based on molecular sequence data from different genes including nuclear ribosomal ITS, plastid rbcL, matK, rpoC1, and others. Fully leafless species are marked with an asterisk (*). The hybrid origin of V. tahitensis from a cross between V. odorata and V. planifolia is highlighted bythe dashed lines. Informal cladeand subclades are labeled on the branch representing the common ancestor of each major species group.

14.5 SYSTEMATIC CONCLUSIONS AND IMPLICATIONS

Considering that Vanilla and its relatives have been surrounded by systematic controversy and uncertainly for such a long time, it is encouraging to witness the increased level of understanding regarding their classification, evolution, and origins that has come about in recent years. The relationship of these orchid species to one another, and to other orchids, has only been clarified during thepastdecade, especially as DNA datahas been incorporated into systematic studies. Up to this point the vanilloid orchids resisted being shoehorned into any particular sub-tribe, tribe, or subfamily of Orchidaceae. We now realize that the single fertile anther of the Vanilla flower’s column arose via a different evolutionary process compared to other orchid subfamilies with similar floral morphology. Future genetic studies into the structure and development of the Vanilla flower/fruit would be well advised to consider other genera of Vanilloideae with shared ancestry, rather than making direct comparisons to more distantly related orchids. Such comparisons could be misleading in their homology assumptions.

In a similar vein, it has become clear that the orchid family is older than previously hypothesized, and that living vanilloid orchids can trace their shared common ancestry back to around 65 million years ago. Through the process of evolution they have become adapted to a variety of habitats, pollinators, and seed dispersal strategies. Yet they share a common suite of genes. Fundamental differences in gene expression and regulation ultimately determine whether a vanilloid orchid is tropical or can survive subzero temperatures, whether it grows as an erect herb in open savannas or as a vine in the forest under-story, and whether it will produce a dry capsule or an aromatic fleshy fruit. As we move forward into the age of genomics, the manipulation of genes will become easier and more common. Future genomic studies, especially those targeting the improvement of Vanilla as a crop plant, may also want to study other closely related genera of tribe Vanilleae or even the entire subfamily Vanilloideae. Imagine the possibilities for increased cultivation potential, for example, if the Vanilla planifolia genome was modified to incorporate genes from Cyrtosia, a closely related erect herb capable of surviving in the cool climate of temperate China. Alternatively, the closely related Epistephium genome might provide clues as to the manner in which many vanilloid orchids exhibit drought tolerance and thrive in the full sun. Future Vanilla plantations might be established in areas with a variety of different climatic conditions as a result of genetic modification, and without a need for structures to support climbing vines.

At the same time that our understanding of Vanilloideae systematics has improved, systematic studies within the genus Vanilla have also broadened our view of its species, both wild and cultivated. Recent publications into the hybrid origin and population genetics of Vanilla tahitensis are the most notable. The genus is more diverse than people in the vanilla industry realize, and there are certainly a number of species other than Vanilla planifolia that produce vanillin and characteristic chemical profiles within their aromatic fruits. Focused breeding among species of the American fragrant Vanilla group would be a logical place to begin, if the development of novel flavors and/or fragrances was a desired goal.