Negative geotropism is one of those interesting agricultural phenomena that might escape you especially if you aren’t looking.
So, what causes that upward bend that is characteristic of bananas when growing on their bunch? Why don’t they just grow straight?
Of course, it’s negative geotropism!
But what exactly is this negative geotropism and why does it have to be bananas.
Well, I have some interesting banana science to add to your agriculture knowledge.
In summary, bananas usually grow with an upward bend due to a botanical phenomenon called negative geotropism where photosensitive hormones auxin causes the banana fruit to bend outwards and upwards in search of sunlight.
What is Negative Geotropism?
Negative geotropism is the opposite of a natural or positive geotropism process whereby plant parts tend to grow towards the ground due to gravitational pull.
Normally, roots and fruits of a plant are meant to respond to the gravitational force that pulls things towards the ground.
But due to some environmental reasons, some plants defy this natural cause for survival.
A good example can be seen in the way the roots of mangrove trees grow upwards to escape the saline conditions on the ground caused by seawater.
But today, we are focusing on something we all know and love. Bananas.
The negative geotropism in bananas occurs due to the presence of a hormone called auxin that I talked about in a separate article here.
Since the green chlorophyll pigments on the banana fruit require sunlight, the hormone auxin forces the fruit to grow towards sunlight.
If the fruits grew straight or facing downwards, the upper layers would obstruct the others below them and deny them access to sunlight.
The weight of the bunch could also easily topple the entire tree.
This is why you may see cultivated bananas being supported by those Y-shaped poles like the one in the picture below.
It is a struggle for survival that the banana fruit had to adapt or perish.
Why are Bananas Curved? The Biological Aspect
The scientific phenomenon of negative geotropism is the reason why bananas are curved when growing on the bunch.
But there is more.
Before man started cultivating bananas, they were wild fruits that naturally grew in some of the world’s dense tropical rain forests.
That environment meant they needed to compete with other taller trees with widespread canopies for light.
Through evolutionary adaptations, bananas developed an epigenetic mechanism to seek out as much sunlight as possible.
This is where the auxins hormones came in.
As the banana fruit grows, more of the auxins move to the fruit apex making it grow in a curve through some complex biological processes that involve changes in pH and osmotic pressure.
This is why the bananas are usually straight in the initial stages of development and only acquire the curvature at the maturity stages.
A banana tree only bears one bunch a year. One bunch can carry more than 100 fruits.
This also means that the fruits have to find a way to reach the sunlight without overwhelming the fragile trunk.
It further explains their negative geotropic curve and the need to stay in compact groups.
Are all Bananas Curved?
Not really. Some varieties do not exhibit this typical banana curvature.
These banana varieties tend to be short, staunch, and firmly straight.
Most of the curved bananas are usually the long fruit varieties that grow on big bunches such as the common Cavendish variety.
The short varieties can easily reach sunlight even in their later stages of development hence do not need to exhibit negative geotropism for survival.
Some examples of these straight varieties include the sweet apple banana, the bluggoe variety, fehi, and the gold finger variety.
Are Curved Banana Varieties More Nutritious than the Straight Varieties?
Well, this is one question that most banana consumers may be asking themselves while selecting bananas on that supermarket shelf.
It is known that most banana consumers subconsciously go for curved bananas with the assumption that they are better than the straight varieties.
Nutritionally speaking, all bananas have almost a similar nutritional profile aside from a few outliers or cross-breeds that may be slightly different.
There may be differences in sweetness, shape, flavor, and color but most bananas are mainly packed with carbohydrates, vitamins, fiber, and essential minerals such as potassium and magnesium.
If you look at the USDA nutritional profile for ripe, slightly ripe, and raw bananas, you will see that the information is similar.
Here are some selected common nutrients in typical banana fruit.
|Nutrient||Quantity in 100g Portion|
|Total dietary fiber||4.62g|
Commercial Benefits of Negative Geotropism in Bananas
Bananas are among the most eaten fruits in the world.
They are also major ingredients in many food processing and food production settings such as baking and food flavoring.
This is because of their nutritional versatility and their availability in many places almost all year round.
To satisfy the huge demand in the market, commercial farmers have developed some selective cultivation techniques to maximize on yield and tackle logistical challenges.
Since bananas are mostly shipped while still intact on their bunches, commercial farmers need to minimize on the space the bunch would occupy in shipping vessels.
To achieve this, synthetic auxin hormones have been used on bananas to induce negative geotropism and maximize on the fruit’s curvature.
This makes the bunch compact and easy to ship since they would occupy less space.
Also, most consumers are used to seeing long curved bananas in the market.
Since this is what banana consumers find appealing, commercial farmers usually take advantage of the negative geotropism phenomenon using hormones to achieve the perfect banana curve.
In conclusion, the curvature seen on bananas is not just a natural thing that has literally no significance in the life cycle of a banana.
It is a product of a series of adaptations that ensured bananas survived their native harsh competitive environment in the tropical forests.
Incidentally, the negative geotropism phenomenon came as a blessing to commercial banana farmers as far as banana logistics are concerned.