Fungus Puts the Heat in Chili Peppers, Study Says

August 11, 2008

There's a fungus among us chili fans—and some of the spicy peppers evolve their kick to repel it, a new study says.

Chili peppers develop piquant chemicals to thwart the harmful microbes long enough to give birds and other animals a chance to disperse the pepper seeds, helping the chilies to procreate, scientists found.

Chilis high in chemicals called capsaicinoids occur most in areas where the fungus can enter the peppers through holes bored by insects, and these chilies are hotter, said study author Joshua Tewksbury, a biologist at the University of Washington in Seattle.

The finding was published online today in the journal Proceedings of the National Academy of Sciences.

The research was funded in part by a grant from the National Geographic Society. (National Geographic News is owned by the National Geographic Society.)

Gradient of Hotness

Tewksbury made the discovery after learning that some species of wild chilies in Bolivia have both pungent, spicy individuals and others that lack any kick whatsoever.

"You can't tell them apart unless you chew on the fruits," he said.

Chewing on fruits—tough field work, Tewksbury joked—helped the team to establish a gradient of hotness along a 185-mile-long (300-kilometer-long) sample area in Bolivia.

The northern end of the line is dominated by nonpungent chilies. The southern populations are much denser and hotter—really hot.

When the team examined fruits from along this transect, they found the pungent ones also had a greater concentration of scar damage from foraging insects similar to aphids and leaf hoppers.

The skin on fruits, Tewksbury explained, is a first line of defense against microbes, which can't get past it on their own.

Continued on Next Page >>


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