Humans have long recognized and taken advantage of genetic variation through traditional plant and animal husbandry techniques. For centuries, selective breeding and conventional hybridization have been used to increase desirable qualities.
For fruits and vegetables, desirable qualities include disease-resistance, drought tolerance, high yield, sweetness, an ability to store well, and color. In the case of apples, humans have also been selecting for diversity. This is a useful but somewhat unique trend as many other widely available fruits come in only a handful of varieties. By contrast, there are around 8,000 different apple types or ”cultivars”. More importantly, most grocery stores are willing to give up valuable real estates to display several different types.
This time of year, I love discovering new varieties of apples at the grocery store or while visiting a near-by pick-your-own orchard.
Each of these types, or cultivars, represents a huge time investment. Using traditional selection methods, breeders first identify parent trees with characteristics that they want and breed them through a process called cross-pollination. Next, seeds from the apples of the mother plant are collected and planted. After a five year wait (the time it takes for an apple seed to grow into a fruit-producing tree), any apples from this second or F1 generation are collected and evaluated.
However, most apple tree offspring tend to be very different from their parents (the opposite of the popular saying “The apple doesn’t fall far from the tree.”). The huge variation created by apple sexual reproduction has earned them the label of extreme heterozygous. This trait may have helped apple trees compete with disease-causing pests in their past evolutionary history and has also allowed the genus to adapt to many environments.
However, for breeders, this variability is a double edged sword. While it can introduce surprising and useful traits/trait combinations, it also limits the control breeders have over the next generation and leads to many more F1 individuals with undesirable qualities. Many apple breeders estimate that only one out of every 5,000 trees created in a crossbreeding experiment will be worth breeding.
Apples that do have crop potential are evaluated on ~50 traits. Some of these traits, such as root stability, can take years to evaluate. This means that it can easily take a decade to ‘discover’ a new apple cultivar.
To ensure the integrity of this hard-won apple cultivar, subsequent apple trees are created through asexual reproduction. In a process known as grafting, branches from the original tree, called scions, are cut from the original tree and grown to generate new trees. Then comes the final challenge – naming the cultivar.
There are thousands of registered apple cultivars. This means lots of different tastes and lots of creative and compelling names. Here’s a list of ten that I’m hoping to try before the fall is over.
1. Smitten – Crips and complex this speckled apple is delicious raw or cooked up in a pie.
2. Jazz – A hard and crisp apple which one taster described as having a “floral pear drop” flavor.
3. SnapDragon – This apple was made by scientists at Cornell University and has a sweet taste with a hint of vanilla and spice.
4. Zestar1! – Sweet and tart this is a delicious apple that also browns easily so has to be eaten fast.
5. Rave – This apple is extra juicy. It’s also harvested in late summer so it’s one of the first apples to arrive on the scene.
6. SweeTango – Current Guinness Book record holder for the crunchiest apple. Enough said.
7. Cosmic Crisp – Crunchy, sweet, tart, and easy for farmers to grow this out of this world apple is widely available and growing rapidly in popularity.
8. Juici – This apple is described as dense, heavy, complex, and crunchy. It also stores well.
9. Pinata – Hailing from Germany, this apple has a crunchy and firm texture and tropical flavor with hints of pineapple and banana.
10. Ruby Frost – Acidic with notes of citrus, this apple also packs a high vitamin c punch.
Apples are a fun and fall-themed way to introduce reproduction, genetics, and genetic engineering to students. Here are five resources to help your class dive deeper:
- TED talk – Why are there so many types of apples?
- Popular Science article – How we breed the best (and worst) apples
- Lesson plan by National Association of Biology Teachers – Tasty Traits: Introduce Genetics with a Sensory Assessment of Apples
- Lesson plan for middle school students – Apple Genetics
- Nature article – Apple whole genome sequences: recent advances and new prospects