A vanilla Vanilla
The orchid that produces the favorite flavor has low genetic diversity, may face risk from pathogens
Scientists have now tasted the genetic makeup of Vanilla, the orchid whose pods bestow flavor on ice cream, perfume and rum. Their findings? It’s pretty plain.
Genetic diversity in Vanilla planifolia is “Very, very, very low,” says Pascale Besse, who led the research, which will appear in the July American Journal of Botany. Besse and colleagues examined a stretch of genetic code in more than 300 vanilla plants from Réunion island, Madagascar, French Polynesia, Mexico, Central America and Brazil.
The findings are worrisome, the researchers say. The blandness of the plant’s DNA suggests that cultivated vanilla is a monoculture, lacking the genetic variation that would help in a face-off with pests or disease.
But even with Plain Jane DNA, there is consistent physical variation among the surveyed orchids — differences in leaf shape and size, pod shape, stem thickness and self-fertility, the researchers report. This physical variation in vanilla plants, without the variation at the genetic level, suggests some intriguing things might be going on — perhaps epigenetic modifications that don’t actually alter the DNA code but can crank up the volume of certain genes while silencing others.
“This opens the doors to a lot of research,” comments botanist Ken Cameron of the University of Wisconsin-Madison, who says that other work has shown interesting chromosomal traits in vanilla. The new report “is pretty exciting,” he says. And “it shines a light of hope for the crop that it will exist in the future even if it is a monoculture now.”
The research also supports current notions of vanilla’s movement around the globe. Roughly 95 percent of the estimated 2,300 metric tons of vanilla beans sold each year are the pods of Vanilla planifolia, predominately grown on the Indian Ocean islands of Réunion (formerly Bourbon), Comoros and Madagascar. But V. planifolia is native to Mexico. There are five recorded introductions of the plant to Réunion island, says Besse, a plant geneticist at the joint research center PVBMT Cirad and University of Réunion. “All the individuals grown here are virtually identical genetically,” she says. And the samples collected from Mexico are the same genetically as the Réunion plants.
The genetic similarity with vanilla plants from all over the place is consistent with records suggesting that a single plant was introduced from Mexico to the West Indies, and then brought to Europe in the early 19th century by the Marquis of Blanford. The exotic specimen then spread further via botanical gardens of Paris and Antwerp. Vanilla probably first arrived on Réunion island during this excursion. One genetic individual survived, and then there was a second diaspora out of the Indian Ocean region, such that plants in cultivation around the world are probably all derived from the original Mexican specimen.
And little has happened to the plant in the intervening years. Unlike corn or rice or roses, which have been bred like crazy, growers basically care for the plant, pollinate it and then let it do its thing.
“Vanilla is still essentially a wild crop that’s treated in the same way it always has been,” says Cameron. “It’s really odd. It is one of those crops that’s being farmed, marketed and processed in the same way it has for hundreds of years.”
That’s not to say vanilla isn’t high-maintenance. On the contrary — its vines must be surveyed daily for new flowers, which must be hand pollinated in the mornings. The task is still carried out by the same method reportedly established by a young slave on the island in the early 1800s — a tiny flap of tissue that separates the sexual parts is poked aside with a little stick and then male and female parts are squeezed together. (The original pollinator is unknown, says Cameron, but was likely a small bee that got pollen on its thorax backing out of the flower.)
Considering vanilla’s lack of genetic diversity, Cameron is especially curious about diversity in the plant’s biochemical pathways. Different cultures prefer different vanilla bouquets, and may favor a hint of brown sugar or tobacco to a more flowery scent.
“By many estimates, vanilla flavor and fragrance is the most popular on Earth — it’s in thousands of products,” say Cameron. Tapping into the biochemical diversity, investigating hybrids, and more research into some of the other 50 to 90 related species could provide a lot of variation for breeders to work with. “There’s nothing plain about vanilla,” he says.
