The banana stands out in the fruit section because it is strange; a long, curved, yellow fruit amongst the rounder red, blue, and purple fruits. But for all of our love for the peculiar fruit, it is endangered, due to a disease called Fusarium wilt. Fusarium wilt, caused by a fungus called Fusarium oxysporum f.sp cubense tropical race 4 (TR4), began its attack on bananas in Southeast Asia in the 1990s and exploded across global banana-producing regions, leaving behind a wake of wilted, discolored trees with no viable fruit. Since the emergence of the disease, countless preventions and treatments have been tried without success resulting in diminished banana supply affecting people in the U.S. and in developing countries alike. That’s why agricultural researchers at the International Institute for Tropical Agriculture, IITA, or a new start-up called Tropic Biosciences are turning to genetic modification to breed a new banana that can withstand Fusarium wilt.
The banana we know was plucked from its tree because it was a mutant, a lone tree producing yellow bananas in a grove of small, red bananas. Unlike other red bananas, which had to be cooked before consumed, the mutant yellow banana was tasty when it was raw. Because the yellow bananas were mutant themselves, any new tree that was planted started as a sucker or side-shoot of an existing tree. Soon banana groves in Latin America, Australia, Southeast Asia, or Sub-Saharan Africa were populated with thousands of trees with the exact same genetics. However, it’s nemesis, TR4, quickly rose up to challenge the banana craze. TR4 saw the genetically-identical plantations as an opportunity, a smorgasbord of its favorite food.
The crisis of bananas vs. TR4 is a case study in the dangers of monocultures. An entire field of plants with the exact same weapons is left defenseless if their weapons are outmatched. Encouraging plantings of diverse plants species and individuals allows an ecosystem to bounce back when threats do emerge. But at this point, if we want to continue the production of our favorite fruit, we need to focus on the plant’s genetics as well.
Plant breeding has been around since the advent of agriculture. It’s how we got corn or wheat from native grasses and the wide variety of crops we grow. Humans have always been selective about the plants and traits they desire and grow. But in the past, we planted seeds and hoped for the best. When researchers discovered DNA in the 1960s, we gained a better sense of the exchange of chromosomes that happens during reproduction and were able to be more particular about the crop traits we were hoping for. The traits that we love about bananas, their amount of fruit and seedlessness is a result of being triploid. Instead of two sets of chromosomes like humans have, bananas have three sets of chromosomes which often renders them sterile. In order to get a new banana variety, breeding involves tedious steps of crossing bananas, planting a new tree, and waiting to see if the banana actually has the desired trait, which can take up to ten years.
There is another option available to us besides traditional breeding called gene-edited crops, or GECs. Like producing GMOs, creating a GEC does involve taking a fragment of DNA and inserting it into the genome sequence of a crop, but unlike GMOs, the DNA fragments aren’t from different species but the exact same one. While our favorite, yellow banana doesn’t have the genetic ability to defend itself against TR4, other bananas do. Researchers can determine what part of the red or green bananas genome causes immunity and “copy and paste” those sequences into yellow bananas. GECs have the potential to help create more disease-resistant or drought-resistant crops while using traits already available in the plant population.
What makes GECs especially important for bananas is that traditionally breeding bananas is complex and unreliable. While this tool isn’t a panacea and we should strive for agricultural systems that are diverse and sustainable, gene-editing is an assistance in an ever-changing world. Hopefully, through the addition of gene-editing techniques to our crop production tool belt, we can continue to produce and preserve important crops, even the curved, yellow banana.