Vitis Vinifera was brought to America by the Spaniards (and others). In Chile, they are still as originally planted (without American rootstocks) because Phylloxera never arrived there due to strict control on imports. So, no indigenous, but on their original roots. Regarding irrigation, it is permitted and absolutely necessary in many denominations around the world, where rainfall levels are not sufficient for vine growth. This still allows the terroir to display and vintage variation, as it does not only depend on water levels but many other climatological aspects. Good questions, though