r - How can two strings be concatenated?

How can I concatenate (merge, combine) two
values?
For example I
have:

tmp =
            cbind("GAD", "AB")
tmp
# [,1] [,2]
# [1,] "GAD"
            "AB"

My goal is to
concatenate the two values in "tmp" to one string:

tmp_new =
            "GAD,AB"

Which
function can do this for me?