How about them apples?

The first couple weeks of October mean apple harvest time for many growers, but how much do you really know about this common fruit?

English: Apples on an apple-tree. Ukraine. Рус...

English: Apples on an apple-tree. Ukraine. Русский: Яблоня со спелыми плодами. Украина. Latina: Malus domestica (Borkh., 1803) (Photo credit: Wikipedia)

In the botanical world, the apple tree is known as Malus domestica, but the genetic diversity of this species has spawned 7500 different cultivars. These varieties have different characteristics- some are good for eating raw, while others are better for cooking and still others are useful for making cider. They come in different sizes, harvest times and colors. Have a look at the list for some descriptions.

If you think about apple cultivation at all (and I know you probably don’t), you conjure up images of the folklore character Johnny Appleseed planting apple seeds ahead of the westward expansion of America. However, this technique couldn’t be farther from the truth of how apples are actually grown. It’s true that apple trees can be readily grown from seed, but don’t expect that tree to give you the same kind of apple as the parent of that seed. The genetic variability of apples will almost guarantee you something inedible if you start from a seed. So how do we grow orchards of our favorite apples? Apple growers use a technique called grafting to keep our orchards stocked with our favorite varieties. In this technique, one plant variety is chosen as the rootstock to be the base of the developing tree and another desirable variety is chosen to be the scion. The top of the rootstock plant is removed or cut and pieces of the scion variety are bound to the rootstock. Eventually these two pieces heal together to form a healthy chimeric plant. The rootstock variety determines some characteristics like tree size and shape, cold-hardiness and disease resistance, while the scion variety becomes the part of the plant that produces the fruit.

With all of that natural genetic diversity and the possible combinations from grafting, it’s no wonder there are so many different kinds of apples. This is where some interesting science begins. The genome sequence of the apple (Golden Delicious variety, if you were wondering) was completed in 2010. It’s 17 chromosomes total about 742 million nucleotides and encode about 57,000 genes. For reference, the human genome has 23 chromosomes totaling 3 billion nucleotides but only encodes for ~30,000 genes. Researchers hope that this new genomic information will provide new genetic markers to aid in breeding programs to develop apple trees that are more disease resistant or have other advantageous properties for growers and consumers.

Researchers are constantly trying to improve upon the apple. A lot of this research is done as part of agricultural experimental stations and universities in top apple-producing states like Washington, New York and Minnesota. For more than you ever wanted to know about how apples are evaluated, check out this slide show for the apple phenotyping protocol used by RosBREED (a national initiative for fruit breeding). The University of Minnesota has developed varieties like Honeycrisp and SweeTango, which are some of my personal favorites. But even as these varieties are gaining substantial market shares, still newer varieties are poised to overtake them. The Sweet RiverBelle is even newer than the Honeycrisp. This year, Cornell University has also released a couple of hot new varieties on the market: SnapDragon and RubyFrost.

But it’s not all juiciness, crisp and storage properties when it comes to apples. Scientists are also working on overhauling the orchard altogether. For this, you have to pay more attention to the plant material that serves as the rootstock instead of the scion that produces the fruit. The rootstock material can determine several valuable properties of apple trees unrelated to the look and flavor of the fruit. For example, they confer root-disease resistance, cold tolerance as well as the size and the time to maturity of the tree. Dwarf rootstock varieties produce much smaller trees with years cut off the maturity time. This makes it faster to get new varieties to market and smaller trees can be easier for growers to manage. Think fewer ladders and an apple orchard that looks more like a vineyard. Of course, smaller trees produce fewer pounds of fruit, but this can largely be overcome by the ability to plant more of these smaller trees. The advantages of being quicker on the market with the changing tastes of the public seem to outweigh traditional views of the apple tree and apple orchards.

If that weren’t complicated enough for you, here’s another wrinkle in apple production. Apple trees must cross-pollinate to ensure fruit production. In other words, bringing home a single favorite apple variety in hopes of providing your family with delicious apples won’t work. Since home fruit orchards are a pursuit of delayed gratification, it’s important that you realize this fact now and not 10 – 15 years from now as you curse the fact that your single tree has not produced any fruit yet.* Your local extension office will likely have information about what varieties are best grown together for the best cross-pollination and fruit production. Even though we seem to have cracked the code for getting the most apples, this cross-pollination requirement means that the apple blossoms can discriminate between their own pollen and the pollen of another apple variety. These biochemical signals ensure maximal genetic diversity by preventing their pollen from fertilizing their own ovules. Only non-self pollen can successfully do this. How plants manage to sort this out is an active area of plant biology research.** If researchers can unlock this secret, then maybe one day you will only have to bring home a single fruit tree for your home apple production needs.

Here’s something else about apples. The trees need a certain amount of ‘chilling time’ in order to produce fruit. The buds that will produce the next year’s fruit crop develop during the summer, but then go dormant in the autumn and winter before bursting forth in bloom for pollination in the spring. These dormant buds must experience colder temperatures for certain amounts of time in order to develop properly and set fruit in the following season. This means that you have to pick an apple variety that also has a ‘chilling requirement’ compatible with your growing area. Don’t worry, your local extension offices will have this information for you as well. As far as fruit trees go, apples have some of the longest chilling requirements (800 – 1100 hours below 45 F). This isn’t a problem for everyone in the northern part of the U.S., but you have to be particularly careful if you’d like to try to grow them here in Louisiana (South Louisiana clocks in <300 chilling hours). Apple researchers have been pushing the requirement lower for some newer varieties to allow for cultivation in southern California. As vexing as this aspect of plant biology may be to planning your home orchard, the chilling requirement has also been the focus of much research just to figure out how plants do this. It basically means that plants have a way of ‘counting’ a certain temperature and translating that into a developmental program. There’s loads of genetic and biochemical secrets underlying how these trees develop their fruit. Deciphering these signals means that one day I too may be able to grow apple varieties here in the south.***

You may have also guessed that apples are big business. The US produces more than 900 billion pounds of apples, over half of them sold as fresh fruit, worth more than $2 billion annually. With all of the effort that goes into the production of the perfect apple, you can bet that there’s intellectual property protection on the hot new varieties. Yes, apple varieties are patented by the developers. This means that while these varieties are under patent protection, they cannot be propagated without authorization from the patent holder. For example, the University of Minnesota holds the patent on the Honeycrisp variety and gets $1.30 per tree sold. Its patent was approved in 1991 and is set to expire this November. After that date, nurseries will be able to freely propagate it without paying royalties to the university. A legal FYI for other Honeycrisp enthusiasts- the date applies to the propagation date and not the date of sale. Trees grafted prior to November 2013 are still subject to patent protection. Proceeds from these patents fuel ongoing apple research and breeding efforts, ensuring a bright future for exciting new apple varieties.

So the next time you are in the produce section, at the farmer’s market or on an apple pick at your local orchard, remember the delicious science behind the apples you take home and enjoy. There are many dedicated researchers and growers working behind the scenes to bring you next year’s new variety. Even for the common apple, it turns out that there is always something new under the sun.


* So you should get at least two of the appropriate varieties, but probably more in case 5 years down the line one of your trees dies (wind damage, disease, incompetent lawmower etc.) causing you to wait years more for those precious apples.

** Not all plants have this cross-pollination requirement. Many of your favorites like tomatoes and peppers are perfectly content to ‘self’ pollinate.

*** Then you can call me Johnna Appleseed. Well, probably Johnna Applegraft.



7 thoughts on “How about them apples?

    1. johnnaroose Post author

      Yes, do one about coffee. I’m thinking about adding a page called ‘The Produce Section’ that would have a behind-the-scenes look at different foods and their related plant research. But I need to finish up some other series first!

  1. Kay hortographical

    Great post! In the UK there’s quite a trend for producing “family apple trees” – that’s where several (usually three) different varieties are grafted onto one rootstock. The varieties are generally (if it’s a good nursery!) chosen to ensure cross pollination. That way, you can maximise productivity and suit different family tastes (e.g. cookers and eaters; sweet and sharp flavour) just off the one tree. They’re ideal for small spaces or container gardening. They’re pretty pricey though: the multiple grafting is a fair bit more tricky.

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