Overview of An Apple Is An Ovary: The Science of Apple Breeding (Shortwave, NPR)
This episode explores how apple varieties are made, preserved, and improved — from traditional hand-breeding in orchards to emerging DNA-based selection — through reporting at Cornell Agritech and USDA apple collections. Hosts interview apple breeder Susan Brown and plant geneticist Ben Gutierrez to explain propagation (cloning via grafting), intentional crosses (hand pollination and emasculation), the long timelines and labor involved, and how genetic preservation of wild apples may supply traits for future varieties.
How apple breeding works
Step-by-step process described in the episode
- Propagation (cloning): Most commercial apples are cloned by grafting: a cutting (bud/leaf) is attached to a rootstock so the new tree is genetically identical to the parent (e.g., every Rosalie or Honeycrisp tree of that cultivar).
- Creating new varieties (sexual breeding):
- To make a cross, breeders must prevent natural bee pollination by removing petals and anthers (emasculation) from the seed parent.
- They collect pollen from the chosen pollen parent (using a comb/screen) and store it in vials.
- Breeders hand-pollinate each flower (often twice) during bloom — a highly labor-intensive process.
- Fruits are grown, seeds extracted by hand, and seedlings grafted onto rootstocks to speed maturity.
- Seedlings produce a few fruits that breeders taste-test; most are discarded ("spitters"). The goal is to find the rare exceptional seedling.
- Timeline and scale: Developing a new apple typically takes around 20 years because of growth and multi-stage evaluation.
Why breeders do this — goals and challenges
- Main breeding targets:
- Improved storability (reduce loss from orchard to grocery)
- Disease resistance
- Flavor, texture, color, and horticultural traits (size, shelf life)
- Examples from the episode:
- Honeycrisp is hugely popular but has high loss (only ~40% make it from orchard to store).
- Rosalie is an example of a new cultivar (reported as a Honeycrisp × Fuji cross).
- Challenges:
- Hand-breeding is slow and inefficient.
- Apples cannot self-pollinate to reliably produce identical offspring; each seed is genetically unique, so seed banks alone aren’t sufficient for preservation.
New science: DNA testing and marker-assisted selection
- Researchers aim to read genetic markers of seedlings to predict traits (color, texture, disease resistance) before waiting for fruiting.
- Apples are genetically complex (~54,000 genes), more than humans, so mapping useful markers is difficult and still emerging.
- Marker-assisted selection could dramatically reduce the need to grow and taste thousands of seedlings, but widespread practical adoption requires many more validated markers.
Preservation and genetic diversity
- The USDA and other collections maintain living orchards (not just seed vaults) because seeds produce unpredictable offspring.
- Collections include both domesticated and wild Malus species gathered globally (e.g., Kazakhstan, Turkey).
- Wild accessions may carry disease-resistance alleles or other traits that could be crucial for breeding future cultivars — even if those accessions themselves aren't tasty.
Key facts & numbers
- ~7,500 apple varieties are grown worldwide.
- Breeding a new apple variety typically takes ~20 years.
- Apple genome complexity: ~54,000 genes (higher than human gene count).
- Example cultivar traits: Honeycrisp — popular but has high loss rate from orchard to store (~60% lost).
Notable quotes / moments
- “An apple is an ovary.” — framing the fruit biologically as a fertilized flower ovary.
- “They’re basically cloning their houseplants.” — on grafting/propagation.
- “I create thousands of these hybrids. And then yes, I must eat them.” — Susan Brown on the scale of taste-testing.
Implications & takeaways
- Apple breeding mixes old-school horticulture (hand pollination, grafting) with modern genomics — both are needed now: hands-on selection for flavor, and genetics to speed selection for hard traits.
- Conserving wild apple diversity is a long-game investment: genes from wild relatives may provide resilience and novel traits decades from now.
- For consumers: much of what makes store apples uniform (color, texture, storability) is the result of long, laborious breeding and cloning; diversity exists in smaller orchards and gene collections.
Glossary (brief)
- Propagation / Grafting: copying a cultivar by attaching a cutting to a rootstock so the new tree is genetically identical.
- Emasculation: removing petals and anthers to prevent unwanted pollination from bees.
- Seed parent vs. pollen parent: seed parent is the flower that will bear the fruit with seeds; pollen parent supplies pollen for fertilization.
- Marker-assisted selection: using DNA markers to predict traits in seedlings before they bear fruit.
Reporter/production credits: reported by Hannah Chin; produced by Rachel Carlson; host Emily Kwong; interviews with Susan Brown (Cornell Agritech) and Ben Gutierrez (plant geneticist).