Bananapocalypse? Yep. Sure Looks Like It.

Banana lovers got an alarming piece of news on August 8, 2019: Fusarium Wilt Tropical Race 4 (TR4) – also known as Panama disease TR4 -- has arrived in Latin America, specifically in Colombia. This disease has decimated plantations of Cavendish bananas in Asia and Australia since the 1990s, and its appearance in Colombia prompted the Colombian government to declare a national emergency.

Since Cavendish bananas constitute nearly half of the world’s banana crop, and TR4 will kill off 100% of every Cavendish plantation, the disease’s invasion of the New World, although inevitable, makes bananapocalypse more of a reality for those who depend on Central and South America for their banana supply. Bananas are a significant food staple for people who live where bananas grow; they are the fourth most consumed food crop globally. In the US, a banana shortage might move consumers to eat other fruit. Much of the world, though, has no alternative. Eliminating the TR4 threat is a matter of life and death, on several levels, for the 400 million people who rely on this food.

Are the banana end times really close at hand? Maybe not. I checked on research advances since August 2016, when I wrote my first banana-themed blog. At that time, no fungicide or biological control existed for TR4. Researchers in the Netherlands, Australia and elsewhere are making progress on several fronts.

A Fungus-resistant Cavendish Banana

In 2017 researchers from Queensland University of Technology reported results of three years of field trials testing transgenic Cavendish bananas. Fifteen separate lines of banana received different sets of genetic material that had exhibited Fusarium wilt resistance in other plants and in a species of nematode. The results, which were validated by banana researchers from Wageningen University in the Netherlands, indicated that one line was completely TR4 free and three others demonstrated robust resistance.

This research stimulates hope on at least two fronts. Producing four disease-resistant lines of Cavendish bananas provides four potential crops. Perhaps more exciting is the identification of the first gene that controls resistance to TR4. This gene, RGA2, is present in Cavendish bananas but is not expressed. Figuring out how to turn on this gene consistently would greatly increase the number of TR4-resistant varieties.

The Queensland team has expanded the size of their research plots to test disease resistance and yields.

Disabling the Fusarium Wilt Fungus

Another approach to eliminating TR4’s effects on Cavendish bananas lies in understanding why the fungus attacks these plants mercilessly. In October 2018 Dutch researchers announced that they have isolated a protein in the fusarium pathogen that is apparently responsible for the pathogen’s virulence. A naturally occurring variant of the gene that produces this protein was found to be much less aggressive. Using this knowledge to disable the fusarium fungus could be another way to attack TR4.

Dutch Bananas

Wageningen University experimenters are working with a local produce supplier to test the feasibility of growing bananas hydroponically in greenhouses. Banana plants are grown either on rock wool or coco peat with the addition of a specially tailored nutrient solution, avoiding the use of soil and eliminating soil as a source of TR4. According to Wageningen professor and longtime banana researcher Gert Kema, the experiment is going well. As of December 2018, the first batch of greenhouse-grown bananas was harvested and sent for further ripening.

If hydroponic culture is cost-effective and if consumers approve of the taste of the fruit, this could be a game-changer. Growing bananas closer to consumers eliminates costly, and environmentally unfriendly, shipping. Given the importance of bananas in the food supply of countries where they are currently grown, switching to a non-soil-based culture would stabilize the supply.

Banana Science

Current banana research is not limited to the three breakthroughs reported here. The Wangeningen University group has a longtime commitment to research on banana diseases. Bioversity International sponsors a banana gene bank and partners with smallholder banana growers to identify varieties that resist pests and diseases, tolerate drought and succeed in their particular environments. ProMusa, a network of people involved in banana research, supports a website with news, links to banana research, an image bank, a blog with the enchanting title Under the Peel, and an encyclopedia of banana knowledge.

By the way, Musa is the name of the banana genus in Linnaean plant taxonomy.

¹An oft-repeated statistic is that bananas are the fourth most consumed food globally. A ProMusa blogger pointed out that this "most consumed food" lacks an operational definition. In addition, non-banana-expert readers think of bananas as a sweet fruit and plantains as a separate category. Plantains are cooking bananas, not a separate genus, and not all cooking bananas are plantains.