If you like your chile peppers hot, thank a fungus.
The spicy fruits developed their kick to ward off invading pathogens bent on destroying chile seeds before they could grow into new plants, according to a study published Tuesday. The bigger the threat from microbial invaders, the more pungent the pepper.
“It is a great example of the power of natural selection,” said Joshua Tewksbury, the University of Washington biologist who led the study in the Proceedings of the National Academy of Sciences.
Chiles are native to South America, where heat and humidity nurture the toxic fungus Fusarium semitectum. The fungus enters chiles through puncture holes made by hungry insects.
Chile peppers responded by growing built-in pesticides called capsaicinoids, the chemical compounds that give them their distinctive zesty taste.
Scientists had surmised that capsaicinoids evolved as a defense against invading bugs, be they insects or fungi. The recent discovery of wild chiles with varying amounts of capsaicinoids allowed Tewksbury and his team to test that hypothesis.
The researchers collected samples from seven chile populations in a 618-square-mile area of southeastern Bolivia. They counted the scars on the peppers to gauge the extent of the fungal threat in each group and examined the seeds inside. For any given number of scars, the chilies with more capsaicinoids had fewer infected seeds, according to the study.
Then the team exposed pristine peppers to fungus-carrying bugs.
Fungal loads in spicy chiles were 45 percent to 55 percent lower than in their mild counterparts, the researchers reported.
