WAMU’s Jerry Gray. (Douglas Chevalier/WASHINGTON POST)

Gerald Poulsen, the WAMU radio host known on air as Jerry Gray, whose popular weekday and Saturday afternoon shows helped make the Washington station one of the nation’s principal broadcast outlets for bluegrass music for more than three decades, died Feb. 2 at a hospice facility in Roanoke. He was 78.

He had complications from a heart transplant that he received after suffering a heart attack on the air in 1989, his son Mark Poulsen said.

Much of the radio audience consists of commuters and other motorists in their cars. “When they ride with me,” Mr. Poulsen once told The Washington Post, referring to fans who heard him in his heyday, “they’re out riding on the range.”

Before WAMU (88.5 FM) shifted away from bluegrass programing in 2001 — a move still mourned by many devoted fans of the genre — Mr. Poulsen had amassed an audience of more than 110,000 weekly listeners.

After starting in 1971 at WAMU, the public station licensed to American University, he became host of “The Jerry Gray Show,” filling Saturday afternoons for 30 years with the old-style country music of performers who included Gene Autry, Tex Ritter, Roy Rogers and Patsy Montana.

The show also featured stories based on Mr. Poulsen’s near- encyclopedic knowledge of the form and his upbringing in a bluegrass family. Mark Poulsen said his father chose Gray as his radio name as an allusion to the color of the uniforms worn by the Civil War armies of the South. That was the region where his family came from and bluegrass music originated.

In 1978, Mr. Poulsen began co-hosting (and later hosting) “Bluegrass Country,” a weekday drive-time radio show. In the 1980s, the station devoted as much as 23 hours a week to bluegrass, and its devotees were said to be among WAMU’s most loyal donors during funding drives.

But in 2001, in what was described as a response to surveys of its audience, the station cut back sharply on bluegrass in favor of news and public affairs. Mr. Poulsen left the station and retired to Hardy, Va.

The switch increased the station’s overall popularity, but bluegrass loyalists felt betrayed because WAMU had been Washington’s only broadcast outlet for the music. The fact that Washington had once been known as “the Nashville of bluegrass” only added to the loss.

Mr. Poulsen traced the genre’s popularity in Washington to the Great Depression, which sent many Southerners to the capital for work. His parents were among them.

Washington “was the first big city going north,” he once said, noting that the new arrivals “brought their music with them.”

Mr. Poulsen carried each day’s selections to the studio with him, drawn from his personal collection of more than 12,000 records.

His afternoon shows combined classic and modern bluegrass, chosen not by popularity but by quality.

Mr. Poulsen’s musical upbringing emphasized authenticity. “I didn’t learn to like country music from listening to the radio,” he told the Washington City Paper. Instead, he said, he learned by listening as his relatives played at home.

Those who heard but never saw him would probably not have been surprised to learn that he did his shows in black boots and often wore plaid shirts with pearl snaps.

Gerald Ralph Poulsen was born Oct. 9, 1933, in Washington, the son of a D.C. firefighter. Explaining his twangy, down-home accent, he once told an interviewer, “Well, you always hear that Washington is a Southern city.”

After his 1951 graduation from McKinley Technical High School, he served in the Army, attended American University and studied at a private radio training academy in the Washington area. While a student, he reportedly hosted WAMU’s first country show.

In the late 1960s, he worked for a commercial station in Front Royal that billed itself as “the grandest little station in the nation.” His musical tastes drew the attention of a WAMU official, who offered him a job. Mr. Poulsen’s responsibilities included providing the music.

Survivors include his wife of 52 years, Louise “Kay” Gregory Poulsen of Hardy; five children, Donna Catron of Hardy, Jon Poulsen of Grasonville, Md., Lora Whitehurst of Manteo, N.C., Mark Poulsen of Mason Neck, Va., and Kathryn Dorshimer of Raleigh, N.C.; his mother, Vesta Poulsen of Edwardsville, Ill.; one sister; nine grandchildren; and one great-grandson.

Mr. Poulsen was joined during “The Jerry Gray Show” by an imaginary sidekick called Clyde the Cow. Mr. Poulsen brought in the cow, he once told the City Paper, for companionship.

“There was nobody in the studio but me,” he said, “and I needed somebody to help out, like when I wanted to have some campfire coffee. Half the time he’s laying on the floor sleeping, the idiot.”