How to create dynamic dropdown list in relationship grid property

finally got solution, OnEditStart event the below javascript method will do...

var prop = "name_R" //Rename to your column name _R | Ex: selected_stone_R

var relgrid =  parent.relationships.iframesCollection[parent.relationships.currTabID].contentWindow.grid;

var keys = [];

var values = [];

//=========================

//Add list options here

addOption("key1", "value1")

addOption("key2", "value2")

addOption("key3", "value3")

addOption("key4", "value4")

addOption("key5", "value5")

//=========================

relgrid.columns_Experimental.set(prop, "editType", "FilterComboBox")

relgrid.columns_Experimental.set(prop, "comboList", values, keys)

function addOption(key, value) {

      keys.push(key);

      values.push(value);

}