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Some fungi show up in our diets, while others are capable killers, possessing the potential to wipe out entire species. The Gros Michel banana, sweeter and less prone to bruising, was wiped out in the 1950s by a fungus called Fusarium oxysporum f. sp. cubense Tropical Race 1 (Foc TR1).
While Foc TR1 is no longer a threat, a new race called Foc TR4 is threatening to repeat history. Foc TR4 causes Fusarium wilt, a disease that clogs nutrient-delivering pathways in plants. It grows in infected plants in the xylem, the nutrient- and water-delivering pipeline, leading to rotting and causing plant mortality rates between fifty and eighty percent. Acting within a species complex—a group of closely related strains that appear alike—Foc can infect over one hundred types of crops. Each strain has a shared core genome and a unique accessory genome, which makes it a niche pathogen for specific plants.
In a study published in Nature, scientists compared thirty-six strains of Foc, finding that Foc TR4 was the most potent inducer of Fusarium wilt. Through genome sequencing, the researchers discovered that Foc TR4’s accessory genome allows it to produce and detoxify nitric oxide, a noxious gas. They found that disabling the genes responsible for nitric oxide production and detoxification reduced Foc TR4’s virulence significantly.By targeting Foc TR4’s nitric oxide defense mechanisms, scientists could weaken the fungus and reduce its threat to bananas. This could involve genome editing, fungicide development, or genetic modification of the bananas to resist the wilt or the effects of nitric oxide, offering new ways to protect bananas from extinction.