Wild ancestor of annatto discovered
February 17, 2016
By Peter Moon | Agência FAPESP – Annatto, a condiment and food dye derived from the seeds of Bixa orellana L., has been used for millennia as a body paint by the indigenous people of the Amazon rainforest, who call it urucum. Adopted by the European colonizers as a substitute for the expensive saffron, it is now common in Brazilian cooking. Likewise, it is used as a natural fabric dye.
According to the Brazilian Geography & Statistics Institute (IBGE), the national statistics bureau, the Brazilian production of annatto reached 12,000 metric tons per year in 2012; 60% of that production was used to manufacture food dyes, 30% was used to make fabric dyes, and 10% was exported to be used in the cosmetic industry.
Despite its economic, culinary, cultural and historical importance, the wild plant from which B. orellana was domesticated has remained unknown until now. Researchers at the National Amazon Research Institute (INPA) and at the University of São Paulo’s Luiz de Queiroz (College of Agriculture; ESALQ-USP) have identified the mysterious wild plant that gave rise to the urucum. It is a shrub called Bixa urucurana.
These researchers have also discovered that the domestication originally occurred in the northern part of South America, probably in the Brazilian state of Pará or Rondônia, rather than in the Caribbean, where the oldest paleobotanical records of annatto have been found. The article describing the research that led to the identification of the wild annatto has been published in the journal Economic Botany.
According to Priscila Ambrósio Moreira, a biologist affiliated with INPA, several plants that occur in inhabited areas of the Amazon or that are used by humans are considered to be domesticated because they have substantially changed compared with their wild ancestors. In this sense, these plants have become dependent on human cultivation to be able to propagate.
“This is the case with annatto,” Moreira said. “You don’t find B. orellana with abundant production of red or orange pigment all over the forest. It’s always associated with anthropogenic landscapes,” i.e., areas altered by direct human action. However, the plant’s origin was unknown.
In 1946, an Italian botanist and entomologist, Adolpho Ducke (1876-1959), surmised that the present-day annatto might have originated from a large tree that grows in southwestern Amazonia, Moreira said. How did Ducke think of this hypothesis? “While collecting plants in the area, he heard the locals talking about a wild plant with fruits that resemble those of cultivated annatto. This was Bixa excelsa,” she explained.
The researchers ruled out Ducke’s hypothesis because they reasoned that even by collecting seeds from the forest and sowing them in kitchen gardens or backyards, it would have been unlikely for a 30 m tree (B. excelsa) to evolve into a 2-3 m bush (B. orellana).
Could there be other species of annatto in the Amazon? “Our hypothesis to identify the ancestor of B. orellana was based on botanical evidence and the traditional knowledge of river dwellers in the region regarding the plant’s ecology,” Moreira said.
For example, river dwellers in Pará told her about a wild annatto plant that sprouted spontaneously in backyards that could be hybridized with cultivated annatto. “More importantly, according to these accounts, the first generation of cultivated annatto after hybridization resembled the wild plant more closely in the sense that its seeds yielded more dye – these people’s main use for annatto. This showed that the two species were able to hybridize, but the wild species predominated,” Moreira said.
A literature review brought the researchers’ attention to Carl Ernst Otto Kuntze (1843-1907), a German botanist and naturalist, who described B. orellana in 1891. Over 120 years ago, Kuntze suggested that B. urucurana must be a variety of the same species as the cultivated annatto.
B. urucurana is a wild annatto, and it is a shrub similar to those cultivated by the river dwellers of the Amazon; it is not a tall tree. “The only shrubby species of annatto that has been described is B. urucurana,” Moreira said.
This wild annatto is also found growing in stands or clumps in open areas on the banks of rivers and streams. “We found one stand of about 70 shrubs right next to the river, and several others along the bank of the same river,” Moreira recalled. The pods are smaller and rounder, and the seeds yield little pigment. “The wild species hardly produces any pigment, whereas the domesticated species yields large amounts,” Moreira said. “The seeds are harvested when the fruit is ripe. Then they’re put out to dry. The seeds are covered with a reddish aril, a fleshy envelope, which is the source of the dye.”
Another difference is that in the cultivated annatto, the pods open to expose the seeds when they are ripe; instead, in the wild species, they remain closed. “If B. urucurana really is the wild ancestor of B. orellana, we’re seeing a change in its seed-dispersal capacity that’s an exception to the rule,” Moreira said. “Domestication typically leads to loss of spontaneous seed dispersal. That’s what happened in the case of corn, for example. With annatto, the opposite appears to happen, given that the pods open spontaneously in the domesticated plant. Production of more seeds and more pigment may have indirectly led to pressure for the pod to open when ripe.”
Geography of domestication
Another important consideration for the researchers was the identification of the site where the domestication probably occurred. Archeological records have shown that annatto was used by Paleoindians in the Peruaçu Valley, Minas Gerais State, between 500 and 1,000 years ago. Carbonized seeds, dated to approximately 1,300 BP, have been found by archeologists in Colombia. According to linguistic studies, the pre-Maya name for the plant was used in Central America 2,400 years ago. Traces of its pigments have been found in settlement sites in central Peru 3,000 BP. However, the oldest evidence has come from an archeological site occupied 3,600 years ago on the tiny Caribbean island of Saba, a Dutch possession in the former Netherlands Antilles.
Despite all of these indications, the discovery of wild annatto led the researchers to conclude that the domestication almost certainly occurred in northern South America. This change in the paradigm results from the fact that B. urucurana is not found anywhere else in South America, Central America or the Caribbean. “Perhaps B. urucurana does occur in the Caribbean, although no herbarium has ever recorded the species. If so, it’s probable that just a few individuals managed to disperse that far. In the Amazon, however, there are plenty of recorded occurrences and areas of intense growth, showing that this is the focal point from which distribution spread,” Moreira said.
“Similarly, although there is paleobotanical evidence of annatto in the Caribbean from about 3,600 years ago, its absence in the Amazon doesn’t exclude the possibility that archeologists in the region will find annatto seeds as old as the Caribbean ones.”
To ensure that they have correctly identified the area in which the plant was domesticated, the researchers must await the results of genetic studies that will reveal whether the wild and domestic plants are indeed varieties of the same species. The genetic study is the responsibility of biologist Gabriel Dequigiovanni, a collaborator on the project and a PhD student at ESALQ-USP in Piracicaba, São Paulo State, with a scholarship from FAPESP.
According to Dequigiovanni’s supervisor, Prof. Veasey from the Genetics Department of the ESALQ-USP, the genotyping based on the use of microsatellite markers has been completed. “B. urucurana and B. orellana are distinct species but not totally separate. There must be a gene flow between them,” Veasey said. “Our hypothesis is that they’re different varieties of annatto.”
The next step is the sequencing of the DNA contained in the chloroplasts, the plant cell organelles that carry out photosynthesis. “Dequigiovanni has collected a large number of cultivated and wild annatto samples, as well as herbarium specimens of several species of Bixa and others in the same family. We now plan to compare these in search of a more concrete answer,” said Veasey, who expects the results to be ready by mid-2016. However, one finding is already certain, “It’s hard to know the focal point from which annatto evolved, but we do know where it was domesticated. The center of domestication is southwestern Amazonia,” a long way from the Caribbean.
This research, aimed at identifying the origin of urucum, is coordinated by Charles R. Clement at INPA in Manaus, the capital of the Amazonas State. His laboratory works on identifying and locating the wild ancestors of plants used by humans in the Amazonia, such as tacacá (Sterculia frondosa), biribá (Rollinia mucosa), domesticated manioc (Manihot esculenta), umari (Poraqueiba sericea), cocoa (Theobroma cacao), Brazil nut (Bertholletia excelsa) and pequiá (Aspidosperma vargasii).
“Clement’s research is important to help tell the story of the Amazon from the angle of its plants and their uses since at least 8,000 years ago,” Moreira said. “It also helps us locate areas in the Amazon that should be protected as historic heritage because of the traditional knowledge and practices of river dwellers and indigenous forest peoples.”
The article “The Domestication of Annatto (Bixa orellana) from Bixa urucurana in Amazonia” by Priscila Ambrósio Moreira, Juliana Lins, Gabriel Dequigiovanni, Elizabeth Ann Veasey and Charles R. Clement, published in Economic Botany, can be read at http://link.springer.com/article/10.1007%2Fs12231-015-9304-0.
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