Question: Who founded the radio show that The Carter Sisters joined in 1950 ? 

full_context: Document 1: Ryman Hospitality Properties: Ryman Hospitality Properties, Inc. () is a hotel, resort, entertainment, and media company named after National Historic Landmark the Ryman Auditorium, built as a tabernacle by Captain Thomas G. Ryman in 1892 and later the home of the Grand Ole Opry from 1943-74. The hospitality group was founded by Edward Gaylord. Prior to its public ownership, it was previously a subsidiary of the Oklahoma City-based Oklahoma Publishing Company, which was formerly owned by the Gaylord family for 71 years until 2011. The OPUBCO company was once the longtime publisher of the "Daily Oklahoman" newspaper. Until 2012, the company was known as Gaylord Entertainment Company, and earlier as Gaylord Broadcasting Company. The company has operated as a real estate investment trust since October 1, 2012.
Document 2: Guiding Light: Guiding Light (known as The Guiding Light before 1975) is an American television soap opera listed in "Guinness World Records" as the longest-running drama in television in American history, broadcast on CBS for 57 years from June 30, 1952, until September 18, 2009, preceded by a 19-year broadcast on radio. "Guiding Light" is the longest running soap opera and the fifth-longest running program in all of broadcast history; only the American country music radio program "Grand Ole Opry" (first broadcast in 1925), the BBC religious program "The Daily Service" (1928), the CBS religious program "Music and the Spoken Word" (1929), and the Norwegian children's radio program "Lørdagsbarnetimen" (first aired in 1924, cancelled in 2010) have been on the air longer.
Document 3: Helen Carter: Helen Myrl Carter (September 19, 1927 – June 2, 1998) was an American country music singer. The eldest daughter of Maybelle Carter, she performed with her mother and her younger sisters, June Carter and Anita Carter, as a member of "Mother Maybelle and the Carter Sisters", a pioneering all female country/folk music group. The group was also known as The Carter Family.
Document 4: Anita Carter: Ina Anita Carter (March 31, 1933 – July 29, 1999), the youngest daughter of Ezra and Mother Maybelle Carter, was a versatile American singer who experimented with several different types of music and played upright bass with her sisters Helen Carter and June Carter Cash as The Carter Sisters. The trio joined the "Grand Ole Opry" radio show in 1950 (Anita was 17 years old at the time), opened shows for Elvis Presley, and joined "The Johnny Cash Show" in 1971. As a solo artist, and with her family, Carter recorded for a number of labels including RCA Victor, Cadence, Columbia, Audiograph, United Artists, Liberty and Capitol.
Document 5: Minnie Pearl: Sarah Ophelia Colley Cannon (October 25, 1912 – March 4, 1996), known professionally as Minnie Pearl, was an American country comedian who appeared at the Grand Ole Opry for more than 50 years (from 1940 to 1991) and on the television show "Hee Haw" from 1969 to 1991.
Document 6: June Carter Cash: Valerie June Carter Cash (June 23, 1929 – May 15, 2003) was an American singer, songwriter, actress, dancer, comedian, and author who was a member of the Carter Family and the second wife of singer Johnny Cash. Prior to her marriage to Cash, she was professionally known as June Carter and occasionally was still credited as such after her marriage (as well as on songwriting credits antedating it).
Document 7: The Carter Sisters: The Carter Sisters, (also known as the second version of The Carter Family) were an American singing quartet consisting of Maybelle Carter and her daughters June Carter Cash, Helen Carter, and Anita Carter. Formed during World War II, the group recorded and performed into the 1990s.
Document 8: Mountain Stage: Mountain Stage is a two-hour music radio show, first aired in 1983, produced by West Virginia Public Broadcasting and distributed worldwide by National Public Radio (NPR). Hosted by Larry Groce, the program showcases diverse music, from the traditional to modern. It is recorded before a live audience, usually at the Culture Center Theater in Charleston, West Virginia, but occasionally travels to other venues elsewhere in the United States. Major private funding is provided by the West Virginia-based law firm of Bailey & Glasser LLP, the Charleston WV Convention & Visitors Bureau and Wild, Wonderful West Virginia (West Virginia Division of Tourism).
Document 9: Midwestern Hayride: Midwestern Hayride, sometimes known as Midwest Hayride, was an American country music show originating in the 1930s from radio station WLW and later from television station WLW-T in Cincinnati, Ohio. During the 1950s it was carried nationally by NBC and then ABC television. The program featured live country music (performed mainly by local musicians but on lesser occasions by national stars) and what was then called "hayseed" comedy, much of which was the inspiration for the later TV series "Hee Haw". It is credited as the first country music program regularly broadcast by a national network.
Document 10: Maybelle Carter: "Mother" Maybelle Carter (May 10, 1909 – October 23, 1978) was an American country musician. She is best known as a member of the historic Carter Family act in the 1920s and 1930s and also as a member of Mother Maybelle and the Carter Sisters.
Document 11: Janette Carter: Janette Carter (July 2, 1923 – January 22, 2006) was the last surviving child of A.P. and Sara Carter, of Carter Family musical fame. In 1976, she and community members built an 880-seat amphitheater, the Carter Family Fold, beside the store her father operated in Southwestern Virginia. Today, the Carter Family Fold attracts more than 50,000 visitors a year. She had three children from her first husband: Donald William (deceased), Rita Janette, and James Delaney (Dale). The surviving two reside in her hometown of Maces Spring, (Scott County) Virginia, which is nestled in Poor Valley at the foot of Clinch Mountain. She was awarded the Bess Lomax Hawes NEA National Heritage Award in 2005 for her lifelong advocacy for the performance and preservation of Appalachian music. In 2006 she died and was buried next to her mother, Sara Carter Bayes, and her brother at the Mount Vernon United Methodist Church Cemetery in Maces Spring.
Document 12: Ryman Auditorium: Ryman Auditorium (formerly Grand Ole Opry House and Union Gospel Tabernacle) is a 2,362-seat live performance venue, located at 116 5th Avenue North, in Nashville, Tennessee and is best known as the home of the "Grand Ole Opry" from 1943 to 1974. It is owned and operated by Ryman Hospitality Properties, Inc.
Document 13: Country radio: Country radio refers to radio stations that play country music. Most country radio stations are commercial radio stations, with some exceptions which are public radio stations. Most country radio stations usually play only music which has been officially released to country radio by record labels. The largest owners of country music stations in the United States include iHeartMedia, Cumulus Media, CBS Radio, and Townsquare Media. There are more radio stations in the United States specializing in country music (about 2,100 stations) than any other format, out of a total of about 15,000 radio stations in the US. Country radio stations are very influential in the country music industry, compared to other genres of music.
Document 14: WoodSongs Old-Time Radio Hour: The WoodSongs Old-Time Radio Hour was created, is produced, and is hosted by folksinger Michael Johnathon. The WoodSongs Old-Time Radio Hour is an all volunteer run non-profit organization, and is a worldwide multimedia celebration of grassroots music filmed in front of a live audience. WoodSongs is not a concert, but a one-hour musical conversation focusing on the artists and their music. The WoodSongs Old-Time Radio Hour began in 1998 in a small studio that sat only 20 people. It was recorded on a cassette tape that had to be turned over half way through the broadcast, and was picked up by one radio station, WRVG in Georgetown, Kentucky. In 1999 WoodSongs moved to a 150 seat room at the Lexington Public Library. After selling out 50 shows in a row, the broadcast was moved in 2000 to the Kentucky Theatre where it stayed until January 2013 when it moved to the 540 seat Lyric Theatre & Cultural Arts Center. By 2005 WoodSongs was being aired on 320 radio stations, and by 2013 509 radio stations across North America and Internationally. The radio program is available to both noncommercial and commercial radio stations, one of the few widely distributed radio programs in the United States to be offered to both types of stations. This does not include the addition of the American Forces Network which broadcasts it in 173 nations, to over 1 million listeners worldwide, and every US Naval ship at sea. In Kentucky, KET (Kentucky Educational Television) (PBS) public television airs the show several times a week. It is distributed to public television stations by the National Educational Telecommunications Association. The WoodSongs Old-Time Radio Hour produces 1 show a week for 44 weeks every Monday evening at the Lyric Theatre in Lexington, Kentucky, and has produced over 750 broadcasts that have aired worldwide.
Document 15: Grand Ole Opry: The Grand Ole Opry is a weekly country-music stage concert in Nashville, Tennessee, which was founded on November 28, 1925, by George D. Hay as a one-hour radio "barn dance" on WSM. Currently owned and operated by Opry Entertainment (a division of Ryman Hospitality Properties, Inc.), it is the longest-running radio broadcast in US history, albeit not the longest-running one on a radio network. Dedicated to honoring country music and its history, the Opry showcases a mix of famous singers and contemporary chart-toppers performing country, bluegrass, Americana, folk, gospel, and comedic performances and skits. It attracts hundreds of thousands of visitors from around the world and millions of radio and Internet listeners.
ground_truth: George D. Hay