Are all bananas edible?

If you start asking the question whether all bananas are edible, you are also wondering if some species are perhaps inedible. But questioning the inedibility of bananas begs another question: why shouldn't bananas be eaten if they are inedible?

Some other fruits, like the tomato, are poisonous if they are still green and unripe. Both ripe and unripe bananas are never poisonous, although you might have trouble digesting a truly unripe one.

[Image: fncw.nsw.gov.au]

No, the real difference between edible and inedible bananas is seeds. Edible variants produce fruit without any seeds, whereas inedible bananas produce a myriad of hard pea-sized seeds. This simply means that eating a banana with loads of seeds is almost physically impossible. Added to that is the fact that these inedible bananas mostly have very little pulp in them, because that too is a mutation. A modern edible banana like the ‘Cavendish’ thus has undergone two different mutations that created a hybrid without seeds but with a lot of pulp. Inedible bananas are not just edible bananas with loads of seeds: inedible bananas are usually quite small, with very little pulp and lots of seeds.

I think it is probably better to define inedible bananas as non-edible bananas.

A noteworthy banana: Musa acuminata

The Musa acuminata is a wild banana species and is one of the two ancestors of virtually all modern commercially cultivated bananas (the other one being Musa balbisiana). The origin of the wild banana and its centre of domestication is thought to be the region that stretches from India to Papua New-Guinea and includes Malaysia and Indonesia.

This large herb can reach a height of some seven meters. The individual flowers are white to yellowish-white in color and will grow upwards and away from the ground. The rather slender fruits are in fact berries (botanically speaking) and their size depends on the number and size of the seeds.

[Image: Kurt Stueber]

It was first cultivated by humans some 8000 years ago. Although it is widely assumed that the modern seedless banana is a hybrid of Musa acuminata and Musa balbisiana, in reality its ancestry is unclear. Some hypothesize[1] that the evolution under domestication of cultivated banana hybrids is more likely to have passed through an intermediate hybrid.

The Musa acuminata likes the more humid conditions of the tropical forests, while the Musa balbisiana has evolved to be more comfortable with somewhat drier conditions.

[Image: foragersyear.wordpress.com]

The wild banana species is considered light demanding and intolerant of competition, opportunistically exploiting breaks in the rain forest, such as on river margins[2]. Various parts of the plant, including the male bud, are still widely used as food in several Asian cuisines. That may lead to the suggestion that wild bananas were at first used for other parts and that occasionally finding seedless hybrids may be considered a lucky break.

[1] De Langhe et al: Did backcrossing contribute to the origin of hybrid edible bananas? in Annals of Botany - 2010
[2] Gowen (Editor): Bananas and Plantains - 1995

Cavendish, the man behind the banana

William George Spencer Cavendish, 6th Duke of Devonshire (1790-1858) became the wealthiest man in England when his father died in 1930.

The Duke was an almost obsessive collector of books, paintings, sculptures and orchids. Owning an orchid was considered a status symbol in the first half of the nineteenth century and the desire to own more of these remarkable plants became a mark of the wealthy and established gentry.

[Cavendish, the 6th Duke of Devonshire]

In order to further increase his orchid collection, Cavendish decided that an expedition should be send to India. One of his gardeners, John Gibson, was to lead the expedition and when Gibson arrived back in England two years later, he had collected several thousand plants, including three hundred orchids with well over 100 of them new species.

All sorts of tropical plants were collected and one of them was a banana plant from China. It was named ‘Cavendish’ in honour of the Duke.

Little did William George Spencer Cavendish, 6th Duke of Devonshire, know that his banana would become the world’s most favoured banana.

Antibacterial activity of banana leafs

Bananas grow in tropical regions of the world and the humid conditions in the tropics also favour growth of fungi and bacteria. Any insect that eats off a banana leaf will leave it wounded and prone to attacks from these pathogens. Nature is all about balance and therefore the banana leaf will try to defend itself by creating bioactive compounds.

Scientists[1] have evaluated banana leafs from four different species of banana for antibacterial activity against multi-drug resistant pathogens causing infections.

The study concluded that among the different banana species studied, Musa paradisiaca displayed efficient antibacterial activity followed by Musa acuminata against multi-drug resistant infection causing pathogens. Further studies are needed to identify the specific bioactive compounds.

It is thus possible that sometime in the future new types of antibiotics can be developed from banana leafs. Which is a really positive outlook because most antibiotics that are in use today are in danger of becoming obsolete.

[1] Karuppiah et al: Antibacterial and antioxidant activities of Musa sp. leaf extracts against multidrug resistant clinical pathogens causing nosocomial infection in Asia Pacific Journal of Tropical Biomedicine.

Mixing the Banana Genome

If you are human, your egg cell or sperm cell carries a full set of chromosomes that includes a single copy of each chromosome. Haploid is the term used when a cell has only one set of chromosomes, which is very useful because males and females can then produce offspring that has the characteristics of both parents. The number of haploid cells in sperm and eggs is 23, which results in a diploid number of chromosomes of 46 (twice 23) in complete humans.

So far, so good.

Having more than two sets of chromosomes is called polyploidy and it is most commonly found in plants. Triploids have three sets of chromosomes, tetraploids have four, etc.

Most of the cultivated sweet bananas and plantains are triploid varieties that evolved from the two wild species, Musa acuminata and Musa balbisiana. That proved easy to designate because the former got the genome designation ‘AA’ (from acuminata) and the latter got the genome designation ‘BB’ (from balbisiana)[1].

The formation of homogenomic triploids hybrids with the AAA genotype occurred within Musa acuminata, leading to cultivars that mostly comprise the sweet bananas. Crosses of the diploid and triploid types of Musa acuminata with Musa balbisiana resulted in the formation of heterogenomic triploid hybrids that are mostly plantains (AAB genotype) and other cooking bananas (ABB genotype). Tetraploid bananas do also exist.

[Image: www.frontiersin.org]

Both the ‘Gros Michel’ and the ‘Cavendish’ belong to the genotype AAA. The modern day edible bananas are therefore a maddening mix of wild and cultivated species, varieties and hybrids, all associated with Musa acuminata and Musa balbisiana.

The breeding of bananas needs triploids or tetraploids, rather than diploids, because only those result in virtually seedless bananas. The ‘Cavendish’ does so very rarely set seed that it is considered sterile. But it isn’t.

[1] Simmonds et al: The taxonomy and origins of the cultivated bananas in Journal of Linnean Society of London - 1955

A noteworthy banana: Pink banana

The Pink banana (Musa dasycarpa, formerly known as Musa velutina) is banana species that originated from Assam[1]. This species is known for its strikingly pink flowers. It is a rather smallish banana plant, that is typically used for its ornamental appeal. Normally, its height will not exceed two meters. One of its other appealing aspects is that it usually flowers within a year.

The bananas are borne on erect flower stalks are pink and hairy. The fruit itself is about ten centimeters long, has soft, sweet flesh and is edible. The fruits peel back when ripe. Eating however is made rather difficult because of an abundance of small black seeds.

In other words: if you want to grow an attractive and not too large banana in your own home, the pink banana is certainly a very good choice.

Häkkinen et al: Taxonomic history and identity of Musa dasycarpa, M. velutina and M. assamica (Musaceae) in Southeast Asia in Journal of Systematics and Evolution - 2008. Pdf here.

A noteworthy banana: Musa balbisiana

The Musa balbisiana is a wild banana species and is one of the two ancestors of virtually all modern commercially cultivated bananas (the other one being Musa acuminata). This wild banana species is native to the drier areas of Southeast-Asia, while the Musa acuminate has evolved in the wetter tropical areas. Musa balbisiana may have adopted to drier regions but it does grow perfectly in tropical and subtropical forests of the Philippines, Thailand, New Guinea, India, south China, Malaysia, Burma, Indonesia, and some other countries.

[Musa balbisiana in Kew Gardens]

Like all other bananas, Musa balbisiana is a herb and it grows with lush leaves in clumps and grows with a more upright habit than most cultivated bananas. Flowers grow in clusters with attractive colours that range from red to maroon. The fruit itself is rather small and is blue-ish green or greenish blue in colour. They are considered inedible because of the many pea-sized seeds they contain. However, it is assumed that wild bananas were used to be cooked and consumed in the remote past because otherwise early farmers would not have developed the cultivated wild banana.

[Foto: Warut Roonguthai]

Research[1] suggests that significant genetic differentiation exists among populations of Musa balbisiana in China which may be helpful in finding genes that help combat Panama disease and black Sigatoka.

[1] Ge et al: Population structure of wild bananas, Musa balbisiana, in China determined by SSR fingerprinting and cpDNA PCR-RFLP in Molecular Ecology - 2005

Bananas: A frightful lesson from the past

The wild banana is a giant herb with a fruit that normally contains a mass of hard pea-sized seeds that make it virtually inedible. In the remote past, hunter-gatherers sometimes discovered plants that produced tasty, seedless, soft fruit. But these seedless plants were mutated and by definition sterile. Sometime at the very end of the last ice age, early farmers in Southeast Asia started to cultivate these sterile varieties by replanting cuttings of these mutants.

These days the ‘Cavendish’ is the worlds premier commercially grown banana and that means that means that if some pest or disease emerges in one part of the world, the ‘Cavendish’ may be extinct within a few short years.

A frightening example can be found in the predecessor of the ‘Cavendish’: the ‘Gros Michel’ and until the 1950s this variety dominated the world’s commercial banana business. The ‘Gros Michel’ was discovered by French botanists in Asia in the 1820s and was richer and sweeter in taste than today’s ‘Cavendish’. The ‘Gros Michel’ fell victim to a soil fungus that produced a wilt known as Panama disease. Because all commercially grown bananas were identical ‘Gros Michaels’, they all withered worldwide and mass unemployment quickly followed.

Now, the ‘Cavendish’ is under threat too: it’s under attack from the ever evolving fungi that causes Panama disease and also one that leads to Black Sigatoka. The only way to keep these diseases at bay is heavy spraying with pesticides: forty sprayings of fungicide a year is typical, making the Cavendish the most heavily sprayed food crop in the world.

One wonders if those pesticides could have a detrimental effect on human health. It is no real surprise that women in banana-packing plants in Costa Rica suffer double the average rates of leukemia[1] and birth defects. Furthermore, a fifth of male banana workers are sterile[2], possibly as a result of exposure to dibromochloropropane, which is now banned.

Meanwhile, the latest mutation of Panama disease, called tropical race 4 (TR4) has now reached South Africa, Australia and much of Asia. Millions of banana plants have died in southern China and pesticides cannot control it. So, it is only a matter of time before the disease reaches the commercial plantations of Ecuador, Costa Rica, Honduras, and Colombia.

The problem is that we neglected the fruit’s genetic base in the wild and we risked losing the possible genes they contain. Genes that could be and undermining the future of the fruit.

Normally plant breeders would engineer resistance into a plant that is at risk but you should remember that the banana is sterile and thus that particular route is very difficult. Which begs the question: what can we do to rescue the banana? Recently scientists from Wageningen University in The Netherlands have been trying to ‘unpeel’ the genome of the banana and to their own amazement, the wild banana species for which the genome has been sequenced turned out to be highly resistant to TR4. And that fact alone may turn out to be the most important result because if these scientist can insert this resistance into the ‘tame’ banana, it may even survive.

[1] Wesseling et al: Cancer in banana plantation workers in Costa Rica in Journal of Epidemiology - 1997 
[2] Bretveld et al: Influence of pesticides on male fertility in Scandinavian Journal of Work, Environment and Health -2007

A noteworthy banana: Apple banana

The Apple banana (also known as Latundan banana, Tundan, Silk bananas, Pisang raja sereh or Manzana bananas) are triploid hybrid banana cultivars from the Philippines. It is one of the most common banana cultivars in the Philippines.

Most bananas are nowadays sterile hybrids or cultivars and the Apple banana is no exception: it is actually a hybrid cultivar of the wild seeded bananas Musa balbisiana and Musa acuminate. The apple banana is a triploid (AAB) hybrid[1]. Its full scientific designation is Musa acuminata × M. balbisiana (AAB Group) 'Silk'.

[Image: www.hale-pohaku.com]

Apple bananas are rather stout and plump, with a thick taut peel. The texture of their flesh is firm when young, maturing to tender and creamy when ripe. Apple banana's flavor is a reflection of its name: when young, it is both tangy and sweet with apple nuances. As the fruit ripens, it will develop a far more tropical flavour profile, with notes of pineapple and strawberry.

One of its names, Latundan banana, honours Claude Letoundal, a French missionary from India who introduced the banana in the Philippines where it remains the most popular banana grown on the islands of the Philippines.

The Apple banana is not grown for large scale commercial production, thus its culinary relevance is mainly within its growing region.

[1] Heautea et al: Analysis of induced mutants of Philippine bananas with molecular markers. Pdf here.

Bananas & Tomatoes

More than 400 million people depend on the banana (Musa acuminata) as their staple food. After wheat, rice and corn, banana is the fourth food crop worldwide. Annual production is about 100 million tons.

But the banana faces major problems: the plant is susceptible to a number of fungal diseases. During the middle of the last century, the 'Gros Michel' banana variety was wiped out by the Panama disease, a disease caused by the soil fungus Fusarium oxysporum, which rapidly spread around the world from Central America. It led to the collapse of the banana industry in Latin America, followed by a huge unemployment.

The 'Cavendish' was selected as the successor to the 'Gros Michel': not as tasty, a shorter shelf life and more vulnerable during transport, but resistant to Panama disease. Sadly though, the party lasted only a few decades, because the 'Cavendish' succumbed to a new, mutated variant of the Panama disease.

[Wild banana with its pea-sized seeds]

But 'Cavendish' is also hit hard by Black Sigatoka, a fungal disease caused by Mycosphaerella fijiensis, which emerged on the Fiji Islands and spread rapidly to the other growing areas The not so environmentally friendly solution was excessive spraying of the banana plantations with poison.

But Dutch scientists came to the rescue of the beleaguered banana: Gert Kema, a researcher at the University of Wageningen is trying to build resistance into banana varieties. His promising discovery is that a resistance gene in tomato recognizes the fungus that causes black Sigatoka in banana. That gene is now being incorporated into the banana plant.

The tomato is thus a possible saviour for the banana.

More info can be read here.