It began at WNYC as the program South American Way (November 4, 1940 edition above) and ended up at WQXR as Nights in Latin America. Through it all, the source collection of recordings remained the same (and grew) as the show passed from one family member to another.
Evans Clark - South American Way
Evans Clark was a writer, largely on social and economic issues. He was also a teacher, foundation executive, health care official, housing expert and on the editorial board of The New York Times. But it was during his tenure as Executive Director of the Twentieth Century Fund (1928-1953) that he was able to indulge his love of Latin American music by building a unique collection of more than six thousand discs of both commercial and one-of-a-kind transcriptions containing native folk and popular music from every country south of the U.S. border. He put this collection to good use by sharing it with WNYC listeners from 1940 to 1946 on the weekly program South American Way.  The title and theme music were taken from the popular 1939 song of the same name usually associated with the Andrews Sisters and Carmen Miranda, who sang it in the stage musical Streets of Paris and then on-screen in 1940 for the film Down Argentine Way.
Clark had become interested in Latin American music because he loved dancing and reportedly found Latin American rhythms fascinating. At one point as a member of the Music Committee of Nelson Rockefeller's Office of Co-ordinator of Inter-American Affairs, a federal agency promoting economic cooperation with Latin America in the 1940s, Clark made a series of short trips to Latin America and wrote up his musical findings. Here he emphasized his focus on popular music.
"It appeals to almost everyone instead of to a few sophisticates and, therefore, has a far greater influence. Also, it reflects national traits and characteristics--it gives the 'feel' and atmosphere of a country as concert music never does--even when the latter is based on 'indigenous themes.' " 
Pru Devon - Nights in Latin America
'I remember how we both laughed when I off-handedly asked whether I couldn't take over'...'On further thought the possibility didn't strike her quite so funny; she auditioned for the station and consequently not only took over Mr. Clark's show but originated two of her own.'
The program's primary sponsor was Panagra Airlines and, for a period, Savarin Coffee. The shows were painstakingly researched and produced reams of fan mail, a sampling of which is in the slideshow at the bottom of the page. But first, a typical program from June 25, 1948 by Devon, opening with her standard, "Saludos, amigos!"
Pru Devon performing in the WQXR studio. (Courtesy of Alister and Wendy Sanderson, WQXR Archive Collections)
 Based on scripts on file, it appears that Evans Clark's program also appeared on WQXR for a brief period between Novemeber, 1943 and March, 1944. We're guessing this was a trial of sorts. (Thanks to appraiser Daniel Langan)
 Clark, Evans, Brief Notes on Music in Eight Countries of Latin America : A Report of a Flying Trip to Brazil, Costa Rica, Honduras, Guatemala, Mexico, Nicaragua, Panama, and El Salvador for the Coordinator of Inter-American Affairs, 1941, pg. 2.
 Devon, Pru, unidentified magazine article from 1950s.,
 Hift, Fred, "Latin American Radio Showcase," The New York Times, November 12, 1950, pg. 113.
Special thanks to Alister and Wendy Sanderson and Matthew Barton, Curator at the Library of Congress Sound Division.