I live in Northern California where temperatures can go below freezing in winter. A neighbor has a stand of peach trees that he called "Indian Peaches" and told me they were California native plants. The fruit is smaller, maybe two inches across, has a green exterior skin (not appealing to farm markets, apparently) and the fruit matures in fall, or "Indian Summer" hence the name. The flesh is a mild white with excellent flavor, and I was surprised by how good they tasted. I took a pit and sure enough, grew mine rather easily. The neighbor told me all their trees were grown from seeds (pits) and none are grafted, hybridized, etc. The tree still does need some expert pruning, watering and fertilizing to yield peaches in any number, and I am still learning... but there is no peach leaf curl. Never. I do not spray anything on it. I wonder if you can have your readers report on such trees if anyone is familiar.