New DNA mapping could lead to more nutritious, sustainable pistachios. The climate crisis has brought warmer winters and a drastic reduction in the fog that used to cool California. To do this, the tree must adapt to the new conditions, and deciphering the genetic code makes this possible.
Researchers have created the most comprehensive genomic sequence ever of the pistachio, allowing breeders to develop improved varieties of the tree.
California produces 99% of the pistachios in the United States, with an economic value of about $3 billion to the state. However, the pistachio has been relatively little studied, in part due to a lack of high-quality DNA mapping. Researchers at the University of California, Davis, have now created the most comprehensive and accurate genomic sequence of the pistachio to date, which will enable the cultivation of better, and perhaps more nutritious, varieties. The researchers have also characterized in detail for the first time the developmental stages of pistachios, which will help farmers manage the crops more sustainably.
The study was published in the scientific journal New Phytologist on March 20, 2025.
Scientists have previously sequenced the pistachio's DNA, but according to Professor J. Gray Munro, senior co-author of the study from the Department of Plant Sciences, the new genetic map is much more precise and detailed than its predecessors. "The improvement in accuracy in the new genome sequence is like going from a hand-drawn map to a Google Earth satellite image," he said.
Monroe and his team sequenced the genome of the "Kerman" variety, the most common variety in California.
Climate change challenges
Pistachio trees are relatively drought and salinity tolerant, but they need cold winters to thrive. As winters get warmer due to climate change, growers need new pistachio varieties that can handle higher temperatures. The warmer winters and the disappearance of the fog that once cooled California's Central Valley have caused significant damage to pistachio crops.
Establishing a pistachio plantation is a long-term investment of up to 50 years, so California growers are concerned about the effects of climate change on their crops.
Important developmental stages
The study identified four key stages in nut development – from flowering to harvest – that include a full physiological assessment, including shell hardening and kernel development.
"Understanding the nut's developmental process will help farmers make informed decisions, such as when to water the trees, thus contributing to more sustainable pistachio production," said Prof. Barbara Blanco-Olte, another senior co-author of the study from the Department of Plant Sciences.
Accurate assessment of developmental stages will also provide growers with better strategies for harvesting and preventing damage from insects and fungi.
According to Blanco-Olte, it was important to not only describe the physical changes in pistachios, but also the genetic and molecular factors behind them. The genome sequence includes novel information about the behavior of different genes during the growing season.
Walnut with high nutritional value
Pistachios have long been known as a nutritious food, and now researchers have discovered the genes and pathways that influence their nutritional value. Among other things, pathways for the accumulation of proteins and unsaturated fatty acids, essential for the nut's shelf life and health benefits, have been uncovered.
"We are gaining information about how all the important nutritional values of pistachios are created, and how we can improve them through proper agricultural management," said Blanco-Olte.
This understanding will help scientists cultivate more nutritious pistachio varieties in the future.
The research was funded by the California Pistachio Research Council, the U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture, and the Foundation for Food and Agriculture Research (FFAR).
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