Pear trees offer fragrant spring blossoms and delicious fruit. Understanding how they reproduce is the first step toward a successful harvest. While a few varieties are self-fertile, most common pear trees are self-incompatible and require cross-pollination to set a reliable crop of fruit. Pollination is the transfer of pollen from the anther to the stigma, leading to fertilization and fruit development.
Defining Self-Fertility and Self-Incompatibility
Self-fertile and self-incompatible describe a tree’s genetic capacity to produce fruit using its own pollen. A self-fertile tree can set fruit when pollen is transferred between flowers on the same tree. These trees complete fertilization without a second variety present, though yields often improve with a partner. Some Asian pear varieties and a few European pears, like ‘Conference,’ exhibit this self-fertility trait.
Most European pear cultivars, such as ‘Bartlett’ and ‘Bosc,’ possess gametophytic self-incompatibility (GSI). This genetic mechanism actively prevents fertilization by arresting the growth of the tree’s own pollen tubes within the flower’s style. The pollen tube is stopped before it can reach the ovule. While some self-incompatible varieties may set a small, uneven crop on their own, consistent production depends on pollen from a genetically distinct partner.
Ensuring Successful Cross-Pollination
To ensure an abundant yield, a self-incompatible pear tree requires a second, compatible variety planted nearby to act as a pollinizer. The pollinizer must be a different cultivar, as two trees of the same cloned variety are genetically identical. This genetically different partner ensures the pollen can bypass the GSI mechanism and successfully fertilize the ovules.
The most important factor in selecting a pollinizer is matching the flowering window, known as the bloom time. If the two varieties do not have overlapping bloom periods, cross-pollination cannot occur. Although European and Asian pears can generally cross-pollinate, Asian varieties often bloom later, requiring careful selection to align flowering times. The pollinizer tree should ideally be planted within 50 to 100 feet of the main tree to maximize pollen transfer.
The Role of Pollinating Agents
Pears are primarily insect-pollinated plants, a process known as entomophily, meaning they rely almost entirely on insects to move pollen between flowers. Wind plays only a minimal role in reproduction. Honeybees and native bees, such as mason bees, are the most important carriers of pear pollen.
Pear blossoms are often less attractive to honeybees than other fruit tree flowers due to their pale color and lower nectar production. This sometimes requires twice the concentration of bees compared to other orchards to ensure adequate pollination. Growers should avoid applying pesticides during the bloom period to protect foraging insects. Encouraging a healthy population of bees, especially early-season native species, facilitates the transfer of genetically distinct pollen for a successful fruit set.