Cracking the Pistachio Problem

When pistachio hulls split too early, they open the door to insects and fungi that damage nuts, contaminate harvests, and cost farmers money. While about 4 percent of the overall crop is affected, some cultivars can see hull split reach 40 percent under certain conditions. Now, for the first time, scientists at UC Davis are uncovering why this happens and how it might be prevented, offering new hope for California’s $2 billion pistachio industry.

By closely examining pistachio hulls at the anatomical, cellular, and genetic levels, the research team discovered that changes in pectin, a key cell wall component, cause cells to come unhitched as the fruit ripens. This breakdown leads to cracks and tears in the hull. As Department of Plant Sciences Professor Georgia Drakakaki said, “This is the first time anyone has studied the pistachio hull at the anatomical and cellular level while also looking at gene expression and physiological data.”

Over three years, the team tracked hull development across major California varieties, linking cell size, gene expression, and ripening to different types of hull breakdown. Their findings give breeders new tools to select traits that strengthen hulls, protect crops, and support growers into the future.