Water cranks up the heat in chillies
Paris - Scientists on Wednesday said they had solved a puzzle over why some wild chilli plants yield red-hot fruit but others have fruit which is mild.
The answer lies in exposure to water, they reported in the British journal Proceedings of the Royal Society B: Biological Sciences.
The fiery ingredient in chillies is capsaicinoid, which the fruit exudes to protect itself against a nasty damp-loving fungus called Fusarium.
Researchers led by David Haak of Indiana University went to Bolivia to check capsaicinoid levels in chillies growing along a 300km line.
In the dryer northeast part of the section, only 15 to 20% of the plants had pungent fruit.
The pungency level increased along the line to the wetter southwest, where eventually 100% of plants produced high-capsaicinoid fruit.
High-pungency chilies pay a price - a "tradeoff" in evolutionary biology - for being able to ward off the fungus.
They produce half as many seeds as low-pungency chillies, which produce more seeds to boost chances of reproductive success in dry conditions.
The study looked at a wild strain of chilli, Capsicum chacoense, which is native to South America and has never been cultivated.