Faruq Salama playing accordion on Umm Kulthum's "Ya Msahharni", Cairo, 1971
The Accordion came to the Arabic music scene in Egypt in the early 20th century, and was originally used without any alteration to add a foreign flavor to the music (e.g. on "Sahirtu" by Muhammad Abdel Wahab in 1935). Later it was altered to add new notes (the "quartertones") that allowed it to play many more Arabic maqam scales with good-enough intonation.
The accordion is extremely popular in the Raqs Sharqi (belly dance) and Sha‘bi genres.