Multiple terrains has texture seams between them.

In unity editor, many same ID terrains can brush texture and height like a whole terrian according to TerrianLayer, but it is useful only in editor mode.
My unity program uses multiple terrians and needs SetAlphamap() at run-time to brush texture between terrains. It occurs texture seams here like below.
Is there a resolvent to brush texture between many terrains as a whole terrain at run-time like TerrianLayer in editor mode?
thanks in advance!

Is there any one can help me???