Chili peppers produce capsaicin, the pungent substance that gives the fruit its heat, as a chemical weapon to beat back invading Fusarium fungi and to protect their seeds. However, in dry conditions, the fungi do not thrive and so the plants do not need to produce as much capsaicin to protect themselves. In wetter regions in which the fungus thrives, the pepper plants spice up their defenses. There is a major physiological trade-off, however. Pungent plants have reduced efficiency in water use, so make fewer seeds in dryer areas. Non-pungent plants in wetter areas, make more seeds but these are more likely to be attacked by fungus.
Throwing cold water on red hot chili peppers