Why do apple and pear orchards need compatible varieties for cross-pollination?

Apple and pear orchards require compatible varieties for cross-pollination because many of these trees exhibit self-incompatibility.1

In self-incompatible plants, pollen from the same flower, from another flower on the same tree, or from a tree with an identical genetic constitution fails to germinate or grows too slowly to achieve fertilization. Consequently, these trees cannot produce fruit on their own. By planting compatible varieties—genetically distinct groups that can successfully fertilize one another—growers ensure that viable pollen is transferred to the stigmas, which is essential for proper fruit set, size, shape, and flavor.12

This process is often facilitated by pollinators such as honey bees, which carry pollen between the different, compatible trees in the orchard.32