Thanks guys but i got it myself!!
private void dgvIsland_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
TextBox prodCode = e.Control as TextBox;
if (datagridview1.CurrentCell.ColumnIndex == 2)
{
var source = new AutoCompleteStringCollection();
if (prodCode != null)
{
prodCode.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
prodCode.AutoCompleteSource =AutoCompleteSource.FileSystem;
}
}
else
prodCode.AutoCompleteCustomSource = null;
}