Here’s a graphic picture about the range of crop varieties available to farmers and growers in the United States. A range falling and falling between 1903 and 1983. Of course some of the now-extinct varieties will have been weak, but most of them probably would have been worth conserving. We don’t know what the future holds.
Since the 1980s, genetic modification (GM, genetic engineering) has gone mainstream. I don’t think that’s very good news for biodiversity.