Pyrus calleryana Seeds | Callery Pear
LATIN NAME: Pyrus calleryana
COMMON NAME: Callery Pear
Plant Profile
Before it was a street tree the Callery pear was a rootstock, and that is still the most important thing about it. Fire blight, the bacterial disease caused by Erwinia amylovora, can kill a pear orchard outright, and the roots are the part a grower cannot afford to lose. This Chinese and Korean species tolerates the disease in its root system far better than the European pear it was asked to carry.
The cultivar that made the species famous was selected at a United States plant introduction station in Maryland and released with an important claim attached: because it could not fertilise itself it would set no fruit, drop no mess and seed no hedgerows. That claim was correct as far as it went and wrong in its consequences. ‘Bradford’ is self-incompatible, but it is not sterile.
Pear self-incompatibility is controlled by a single genetic locus that makes a flower reject pollen carrying the same recognition gene as itself, so grafted trees of one cultivar cannot pollinate each other. But street plantings held several cultivars and orchards used the species as stock, so compatible partners were everywhere, and the resulting seed has been carried by birds into fence lines and pastures.
The pattern is now well documented in the eastern United States, where thickets of thorny Callery pear appear along field edges, railway lines and motorway verges. Each thicket reduces pasture, competes with native scrub and resists cutting because the plants re-sprout. Several states have moved to restrict further planting or sale, a remarkable reversal for a municipal ornamental.
In its own country the Callery pear is an unremarkable small tree of open woodland, thickets and river banks in China and Korea: round-headed, often spiny on young growth, with glossy oval leaves and small hard fruits. It flowers early in the season with the leaves, producing flat clusters of small white blooms, each five-petalled and cup-shaped on a branching stalk.
Science & Biotechnology
Pear breeding has made the self-incompatibility locus of the genus a well-studied piece of molecular genetics. The mechanism works through a ribonuclease produced in the style that degrades the RNA of a pollen tube carrying the matching recognition gene, and breeders score the genotypes of their material so that any orchard or avenue contains the partners a crop needs.
Pear fruit and leaf tissue carry a set of phenolic compounds, including arbutin and chlorogenic acid, alongside the sugars and organic acids that decide flavour. Arbutin has drawn attention in food and cosmetic research and occurs across the genus, and the leaves of Pyrus species are a known source of it. In this species the fruit is otherwise useless.
Uses & Benefits
Grafted onto a Callery root, a dessert or culinary pear gets a tolerant, vigorous base with a strong root system that takes both wet and dry spells, and a union that usually knits cleanly. Seedling rootstocks were cheap to raise in bulk, which suited the nursery trade, and on light or difficult soils the combination out-performed trees on their own roots.
The fruit is a pome of about a centimetre and a half, brown when ripe and full of hard stone cells — the same sclereids that make an over-ripe culinary pear gritty, here so numerous that the fruit is unpleasant rather than edible. Birds take them anyway and move the seed. Autumn colour is good in most forms, the glossy leaves turning red and purple.
The tidy fastigiate form of the ornamental selections made Callery pear the default street tree of a generation, but the replacement list is well known: serviceberry, redbud, dogwood, hornbeam and crab apple fill the same niche without seeding into the countryside. Where a tree is needed on a dry verge, a species that will not spread is the sensible choice. Sowing for rootstock begins with clean seed.
Growing from Seed
Mash the ripe fruit and wash the seed out, discarding pulp and skins, then mix the clean seed with damp sand and leave it in a covered pan through a full winter outdoors before sowing in spring. Sow into a bed of loam and grit with the seed about its own depth under the surface, thin the row once the first true leaves have expanded, and lift the whips for budding in their second season.
Our Take
Grow the Callery pear for rootstock and for the early spring bloom, but think twice before planting it where birds can move the fruit into open country. Our pages on the birchleaf pear and on the Ussurian pear describe two Asian species with a better record as garden trees, and Pyrus xerophila is the drought-hardy option for stock work.
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