The current banana industry originated a hundred years ago with the introduction of the banana rhizome (an underground stem) to the Americas from the Caribbean island of Martinique. The variety had thick skin resistant to bruising, the bananas grew close together and could be tightly packed, and the ripening time was long. It was therefore well suited to ship transport and could make a long journey over rough seas.
This banana variety was Gros Michel also called Big Mike. The banana plant was propagated by digging up the stem from the rhizome and planting it back in the soil. This type of reproduction is without meiosis. The crops are therefore all very identical to the first stock. This means that if a disease can infect and destroy one of the plants, it is likely to infect and destroy all the other plants as well.
In the 1950s, banana plantations with Gros Michel were plagued by the Karfusariosis fungus (Fusarium oxysporum). The fungus can live for a long time in the soil and can be transported and spread with plants, soil and water. Banana plants will absorb the fungus through the roots, and then the banana will starve of nutrients. The Fusarium type TR1 caused the banana disease called "Panama disease". The epidemic wiped out the large banana monocultures and in the 60s this banana variety was commercially extinct.
But there was another type of banana, also with good properties for transport, and which was resistant to this banana plague. The new banana type, resistant to the Panama disease of the type TR1, is the variety "Cavendish" and has been cultivated in Latin America for export to North America and Europe since the 60s and until now.
Now the Fusarium disease against bananas from Latin America has returned. The new type of Fusarium was first discovered in 1989 in Taiwan and has spread throughout South and South-East Asia. Thirty years later in 2019, this banana disease was observed for the first time in Colombia. The fungus is called Fusarium oxysporum TR4 and can, as TR1 did to Gros Michel before, destroy all Cavendish plantations in Latin America, thereby eradicating Cavendish bananas there as grown and exported today.
The new type of Karfusariosis disease is caused by the soil fungus Fusarium oxysporum cubense tropical race 4 (TR4). No Cavendish is likely to be resistant to this banana plague. But the wild banana (Musa acuminate malaccensis) in Asia is much more diverse than the Cavendish variety and resistance to TR4 has been discovered there. More specifically, a gene has been discovered in wild bananas that can provide resistance to infections from TR4.
The gene RGA2 from wild banana, inserted into a Cavendish banana plant through genetic engineering, creates Cavendish with higher resistance to Fusarium TR4. To create bananas that are completely resistant to the new banana plague, the Ced9 gene from a roundworm has been inserted into the genetically modified Cavendish. The Ced9 gene is from a roundworm that codes for apoptosis (a type of cell death) that will possibly be caused by Fusarium TR4. This leads to the Cavendish banana, free of T4 symptoms. But, it also involves unintended effects.
Links:
Alarm as devastating banana fungus reaches the Americas
Transgenic Cavendish bananas with resistance to Fusarium wilt tropical race 4
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