They also selected three populations of chili plants that each produced both pungent and non-pungent fruit and spanned the range of rainfall and pungency differences. They then grew seeds from those plants in the UW Botany Greenhouse to examine what affect water availability had on pungency.
The 330 plants that resulted from those seeds were grown under identical conditions until they reached their first flowering, then were separated into two groups one that received plenty of water and one that was stressed by receiving only the amount of water available to plants in the driest area of Bolivia from which seeds were taken.
The scientists found that under water-stressed conditions, non-pungent plants produced twice as many seeds as pungent plants. That suggests the pungent plants trade some level of fitness for protection from the Fusarium fungus, Haak said.
The researchers determined the pungent plants have developed a reduced efficiency in water use, so in dryer areas they produce fewer seeds and are more limited in reproduction. In wetter areas, non-pungent plants are at a reproductive disadvantage because they are much more likely to have their seeds attacked by the fungus.
"It surprised us to find that the tradeoff to produce capsaicin in pungent plants would involve this major physiological process of water-use efficiency," Haak said.
He noted that over the entire range, 90 to 95 percent of the chili fruits had some level of fungal infection, and pungent plants were better able to defend themselves.
|Contact: Vince Stricherz|
University of Washington