Bananas and plantains are a staple food for a large proportion of the population in developing countries. However, they are susceptible to many diseases and pests. just-food.com’s Aaron Priel takes a look at the latest initiative to map the banana’s genome and asks what scientists expect to get out of the research.
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A few months ago, scientists from 11 countries announced the founding of an international consortium to sequence the banana genome within five years. Based in governmental, university and non-profit organisations, the researchers hope to be able to use the new genetic data to enable developing-world farmers to grow bananas that are able to resist the devastating “Black Sigatoka” fungus, as well as other diseases and pests.
“Bananas are a staple food for nearly half a billion people worldwide, but their crops are increasingly lost to disease,” explained non-profit organisation Future Harvest. Funded by the Consultative Group on International Agricultural Research, Future Harvest is an initiative of 16 food and environmental research centres that aims to build awareness and support for food and environmental research that can be used by rural communities in the developing world. A recent report by the group also highlighted the importance of banana research to developed world consumers: “The genome sequence will also benefit US and European consumers of the popular dessert banana, one of the world’s most chemically dependent crops.”
Evolutionary standstill
Ancient farmers selected banana strains that were seedless and thus sterile, and grew the fruit through vegetative sprouting, according to Dr Emile Frison, director of the Montpellier, France-based International Network for the Improvement of Banana and Plantain (INIBAP).
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By GlobalData“Cultivated bananas have, therefore, been at a near evolutionary standstill for thousands of years and lack the genetic diversity needed to fight off disease,” he explains in the Future Harvest report: “A coordinated effort by scientists worldwide is needed to unlock the diversity found in bananas that still grow and reproduce in the wild.”
INIBAP is leading the effort to unlock this diversity through the formation of an umbrella group called the Global Musa (banana) Genomics Consortium. The consortium also involves the Nigeria-based Future Harvest centre International Institute for Tropical Agriculture (IITA) and the Rome-based International Plant Genetic Resources Institute (IPGRI), which brings together organisations from Australia, Belgium, Brazil, the Czech Republic, France, Germany, India, Mexico, the UK, and the US. includes the The Institute for Genomic Research (TIGR), which previously collaborated in sequencing the genomes of rice, Arabidopsis (a plant in the mustard family) and the parasite that causes East Coast fever, a leading cause of death amongst African cattle, is also involved.
The scientists will map the banana genome using a sexually reproducing wild species of banana from Southeast Asia and according to the report, the project will make the banana “the first exclusively tropical crop to be sequenced”.
Staple crop
“More than a popular snack; bananas are a staple food that many African families eat for every meal,” Frison explained: “This is our chance to develop a crop that won’t fail for them and that may help lift them out of hunger and poverty.”
Farmers in 120 countries around the world grow bananas and plantains. Plantains are long, green bananas – one of six major groups of cooking bananas – found mostly in West Africa and Latin America. Of the 95 million metric tons of bananas grown annually, approximately one-third is produced in each of Latin America, Africa, and Asia.
“Bananas and plantains together are the developing world’s fourth most important food crop, following rice, wheat, and corn. In parts of Africa, bananas provide more than one-quarter of all food calories,” the report notes.
When ripe, most banana types are not sweet like the imported dessert Cavendish bananas eaten in Europe and North America, but starchy like a potato and eaten cooked. Banana varieties, all grouped under the scientific name of Musa, are rich in vitamins A, C, and B6 and contain high levels of calcium, potassium, and phosphorous, providing an essential source of nutrition in developing countries.
Fungus threat
Some 85% of the global crop is produced for home consumption and local trade, largely without the use of pesticides, leaving them highly susceptible to disease. The 15% of the global banana crop grown for export relies heavily on chemical inputs, Future Harvest says.
Bananas are threatened by the rapidly spreading fungus Black Sigatoka, which has been undermining production of the crop for the past three decades. “It has reached almost every banana-growing region in the world and typically reduces yield by 30 to 50%,” the report claims. Other diseases and pests that cripple yields include a soil fungus, parasitic worms, weevils, and viruses such as the Banana Streak Virus, which lurks in the banana genome itself.
Chemical input
Commercial growers can afford and rely extensively on chemical fungicides, often spraying their crops 50 times per year, which is about ten times the average for intensive agriculture in industrialised countries. Chemical inputs account for 27% of the production cost of export bananas. Agricultural chemicals used on bananas for diseases and pests have harmed the health of plantation workers and the environment.
Frison argues that if scientists can devise resistant banana varieties, “we could possibly do away with fungicides and pesticides altogether. In addition, resistant strains are essential for small-holder farmers, who cannot afford the expensive chemicals to begin with. When Black Sigatoka strikes, farmers can do little more than watch their plants die, and increased hunger can swiftly follow.”
He added that bananas have unique characteristics that will provide the latest researchers with a powerful model, capable of investigating fundamental questions with potentially widespread applications to agriculture.
Highlighting those characteristics, Frison noted that bananas originated in Asia, before being introduced to Africa several thousands of years ago. The wild bananas that remained in Asia continued to co-evolve with their pests, while the African arrivals left most of their pests behind. Comparing the genomes of wild Asian varieties with those of African cultivars will provide scientists with an uncommon look at the effects of disease agents on genome evolution.
Furthermore, bananas are the only known plant in which a virus (The Banana Streak Virus) imbeds pieces of itself into the banana’s own DNA, only to pop out during times of stress, reassemble itself, and cause disease. The banana genome sequence should reveal just how this virus is able to strike when the plant is most vulnerable and it is hoped that it will provide a powerful new tool for targeting genetic transformation.
By Aaron Priel, just-food.com correspondent
