In a laboratory in the mid-1970s, Mary-Dell Chilton kept getting a result her training told her should not exist: DNA from a soil bacterium was sitting stitched into the chromosomes of the plant cells it had infected. Chilton, the biochemist whose insistence on that improbable result helped produce the world's first genetically modified plant, died on June 24, 2026, at her home in Carrboro, North Carolina, at 87.

She was born February 2, 1939, in Indianapolis, Indiana, and grew up mostly in Southern Pines, North Carolina, raised by her grandmother. Her son, Mark Chilton, later said his mother's grandmother had been probably the single biggest influence on her life: a woman who, without ever saying so, showed a granddaughter watching her that there was no reason she could not become a chemist. Mark Chilton still has stacks of handwritten letters his mother and her grandmother exchanged through her college years and up until her grandmother's death.

Chilton earned a bachelor's degree in chemistry from the University of Illinois Urbana-Champaign in 1960 and a doctorate there in 1967, then joined the University of Washington faculty in Seattle to study the biochemistry of plant cells. "When I was a graduate student, we were just beginning to work out the genetic code, and I was tickled to death by the experiments," she said of those years, a drive she later summed up more bluntly: "You can't stop me. When I'm after something, I work on it endlessly until I get it."

It was at Washington that Chilton and her colleagues found fragments of Ti plasmid DNA from Agrobacterium tumefaciens, the soil bacterium that causes crown gall disease, integrated into the nuclear DNA of the plant's own tumor cells, work published in the journal Cell in 1977 according to a tribute from France's Institut de biologie moléculaire des plantes. The result upended what plant biologists assumed was possible, so much so that the team repeated the work before trusting it. "We had to perform the experiment repeatedly because the outcome was so surprising," she said afterward.

In 1979 she moved to Washington University in St. Louis, where her team showed that the disease-causing genes on the Ti plasmid could be stripped out without disabling its ability to ferry other genes into a plant's chromosomes, turning the bacterium's own infection machinery into a delivery system, according to the university's own account of her work at the Washington University commencement archive. Three years later, in 1982, her lab used that disarmed Agrobacterium to insert a chosen gene into tobacco cells and regenerate them into whole, fertile plants that passed the new trait to their offspring, the achievement now generally credited as the world's first genetically modified plant.

Chilton left the university in 1983 to found the first agricultural biotechnology research laboratory at Ciba-Geigy Corporation, in Research Triangle Park, North Carolina, a company that became Syngenta. Over a 35-year career there she rose to Vice President of Agricultural Biotechnology and Distinguished Science Fellow, work that helped bring Syngenta's early biotech corn traits to market before she retired in 2018.

Honors followed the research for decades: the Benjamin Franklin Medal in Life Sciences in 2002, The News & Observer's Tar Heel of the Year in 2013, and, that same year, the World Food Prize, shared with Marc Van Montagu and Robert Fraley. "Millions of farmers all over the world have Dr. Chilton to thank for protecting their crops from disease, pests and climate shocks," World Food Prize Foundation chief executive Tom Vilsack said after her death. Washington University had already named its Mary-Dell Chilton Distinguished Professorship in Arts and Sciences after her in 2009, installing biologist Barbara A. Schaal as its first holder, and gave her an honorary doctor of science degree in 2015, the same year she entered the National Inventors Hall of Fame. In 2023, President Joe Biden presented her with the National Medal of Technology and Innovation; Justin Wolfe, president of Syngenta Seeds, called her "a true trailblazer and icon in our industry" in a statement from Syngenta Group.

Outside the lab, Chilton kept the same stubbornness that drove her science. At 76 she paddled her own canoe the length of Utah's Stillwater Canyon on the Green River, refusing her son's repeated offers to take over. "She did wind up in the hospital, but she made it all the way," Mark Chilton said. "I tried and tried to get her to stop paddling and let me just paddle the canoe, but she would not." She was also an avid card player and dog lover, according to WRAL.

She is survived by her sons, Mark and Andrew Chilton, and two grandchildren. Mark Chilton served as mayor of Carrboro, North Carolina, from 2005 to 2013.

The disarmed Agrobacterium Chilton engineered remains the basic tool researchers still use to insert genes into crop plants worldwide, quiet infrastructure behind decades of pest-resistant corn, cotton and soybeans. Washington University fills an endowed chair that carries her name, and a case in the National Inventors Hall of Fame holds the patent that grew out of her Ti plasmid work. It is, in the end, a straight line back to a girl in Southern Pines who watched her grandmother do what no other woman in town was doing, and decided the same rule applied to her.