Then-Lieutenant William Bligh was the captain of the HMS Bounty when the ship’s mutiny occurred in 1789. After being set adrift in Bounty’s launch by the mutineers on board, Bligh and 18 sailors who remained loyal to him and were thrown aboard all reached the southeast Asian island of Timor.
Many people might be familiar with Bligh from Mutiny on the Bounty, a classic book and a film starring Clark Gable that fictionalized the arduous journey and mission’s ultimate failure. The film was later remade twice, with Marlon Brando in 1962 and Anthony Hopkins in 1984.
In 1793, Bligh docked another ship, the HMS Providence, in Kingstown in St. Vincent and the Grenadines, a small island nation in the Caribbean Sea, with cargo filled with several hundred sapling breadfruit trees. His goal was unique – to introduce the long-lived trees with their carbohydrate-rich fruits to cheaply feed Britain’s slaves who labored on the islands’ sugar plantations.
Five lineages of breadfruit
The expedition failed to inventory what types of breadfruit they introduced. Caribbean people cared for the breadfruit, enabling it to thrive. Now, 230 years later, a plant biology team led by Northwestern University, the Chicago Botanic Garden and the St. Vincent Botanical Gardens has, for the first time, traced five major lineages of Caribbean breadfruit back to that single introduction from Bligh’s voyage.
Seventeen years after the Bounty mutiny in 1806, he was appointed governor of New South Wales in Australia with orders to clean up the corrupt rum trade of the New South Wales Corps. His actions directed against the trade triggered the Rum Rebellion, during which Bligh was placed under arrest and deposed from his command, an act that the British Foreign Office later declared to be illegal. He died in London on December 7, 1817.
For the first time, the team identified five lineages in the Caribbean and connected them to the original Tahitian lineages introduced in 1793. Not only have the original breadfruit tree cultivars (or varieties produced by selective breeding) survived for centuries, they also are thriving, the researchers found.
The study has just been published in the journal Current Biology under the title “Linking breadfruit cultivar names across the globe connects histories after 230 years of separation,” on the 230th anniversary of Bligh’s arrival in the Caribbean. “Breadfruit is an underutilized crop, and it doesn’t get nearly as much attention as the major crops. However, interest in breadfruit is increasing globally, and we thought this would be a fascinating puzzle to solve,” said Nyree Zerega, the study’s senior author.
An important crop for food security
“Outside of Oceania, the Caribbean is one of the largest producers of breadfruit worldwide,” added Lauren Audi, the study’s first author. “We really don’t know much about the genetic diversity of the fruit in the Caribbean. Because this is an important crop for food security – especially for island nations that are highly susceptible to climate change – we wanted to characterize the genetic diversity of breadfruit crops in order to conserve them. The first step for that is to characterize the diversity of what we already have.”
A breadfruit expert, Zerega is director of the Program in Plant Biology and Conservation of Northwestern’s Weinberg College of Arts and Sciences and the Chicago Botanic Garden, Audi was a graduate student in Zerega’s laboratory at the time of the research and is now a lab manager at the Sackler Institute for Comparative Genomics at the American Museum of Natural History in New York.
“When you look at the logs from the Bounty, Bligh carefully documented what was collected,” Zerega said. “But on his second voyage, the time spent in Tahiti was shorter, and there weren’t any notes about the names of the breadfruit cultivars they actually collected. He did indicate that five kinds of seedless breadfruit were collected, but subsequent historical texts have suggested different numbers. Wanting to know this is partly curiosity, but it’s also useful because it links cross-cultural knowledge about the plants.”
The lack of historical records from Providence is not the only reason why characterizing breadfruit genetic diversity in the Caribbean has been challenging. There are several genetic challenges – seedless breadfruit trees have three copies of chromosomes, instead of two, which is more common. There are not as many genetic tools designed to analyze triploids compared to diploids.
Triploid breadfruit trees also are unable to reproduce sexually and can only survive if humans propagate them by cloning. “When you bite into a honey crisp apple, you expect a different taste and texture than a McIntosh,” Zerega explained. “Clonal propagation ensures that you get what you expect. When plants develop seeds through sexual reproduction, they give rise to variation in offspring – just like the variation among human siblings.”
Over thousands of years of clonal propagation, however, variation can still arise due to somatic mutations, which are mutations in the tree’s non-reproductive cells. Somatic mutations can occur spontaneously, due to stress or errors in DNA repair. In search of the best fruits, humans sometimes select the part of the plant where the somatic mutation occurred and propagate it. So, if the mutation gives rise to a desirable new leaf or fruit type, people can cut the branch where the mutation occurred, propagate it and essentially clone that new mutation to grow a tree with the desirable fruit again.
The researchers combined local knowledge with historical documents and specimens, observations about the fruit’s size, shape, texture and targeted genome sequencing. They traveled throughout St. Vincent, collecting leaves and taking measurements of leaf and fruit size and shape. Then, they supplemented these samples with historical dried, pressed specimens stored in herbaria in museums and botanic gardens around the world – including a specimen collected in 1769 from the HMS Endeavor voyage led by Captain James Cook. Finally, the scientists were able to provide answers to a centuries-old mystery as to which kind of breadfruit was cultivated by Bligh.
Although breadfruit began with a dark history in the Caribbean as slave food, the nutritious fruit eventually became an important part of island diet and culture. Despite having “fruit” in its name, breadfruit is starchy and seedless, playing a culinary role more like a potato. Closely related to jackfruit, the nutrient-rich food is high in fiber, vitamins and minerals.
In its native Oceania where breadfruit was domesticated, people have been eating breadfruit for thousands of years – steamed, roasted, fried or fermented. Breadfruit also can be turned into flour to lengthen its shelf life. Once established, a single breadfruit tree can live for decades, producing a large number of fruits each year, and, because it’s a perennial crop, it also requires less water and fertilizer than annual crops that must be replanted each year. Like other trees, it also removes carbon dioxide from the atmosphere.