A hundred and fifty years ago, there were thousands of named varieties of apples in North America. Today, most of them have disappeared. As pests and diseases evolve, and with the need to adapt to emerging conditions (climate change, anyone?), we need diverse apple genetics more than ever. But, that genetic diversity is threatened.
Dr. C. Thomas Chao, USDA apple collection curator, describes the collection to a tour group. USDA has a world-class collection of apples in Geneva, NY, including the group of Malus sieversii individuals we are acquiring. (c) 2015, Eric Johnson
The genome of the domestic apple is derived mostly from a couple of wild species, including in particular Malus sieversii, which is native to Central Asia. As apple seeds were traded and grown westward along the Silk Road, the available pool of genes was narrowed, so that historical European apples carried less overall diversity than their relatives in Central Asia. The apples brought from Europe to North America resulted in further genetic narrowing, although the “Johnny Appleseed” phenomenon of planting randomly cross-pollinated apple seeds did result in a expansion of apple varieties here. Add in industrial agriculture’s focus on a dozen or so types, many of which are closely related to one another, and the picture for the future of the apple production is uncertain.
At the same time, Malus sieversii populations are under pressure in Central Asia, through clearing of forests for development, harvest for firewood, etc. This has truly disastrous potential, as the entire world is dependent on those forests for new genes to improve domesticated apples.
Fortunately the situation has begun to change. There are projects in Central Asia to protect wild apples, and breeders are working with these wild apples all over the world.
Close to home, USDA personnel and researchers in host countries collected seeds in the 1990s from threatened wild apple populations across Central Asia, in order to propagate the species and conserve genetic diversity. Collection localities ranged from moist, high-latitude sites with extreme winters to dry, lower-latitude hilltops with thin soils and less precipitation than Boulder typically receives. USDA established an orchard of more than a thousand Malus sieversii seedlings at Geneva, New York for use in breeding and research. Phil Forsline, one of the USDA scientists involved in these expeditions, estimates that these expeditions “more than doubled” the available apple biodiversity in North America. Already, this collection has been important in developing disease-resistant rootstocks that are starting to be used by apple growers.
Scientists have also assessed the genetic diversity of these trees and identified “core collections” of individuals that include the great majority of the diversity likely to be found in the M. sieversii orchard in Geneva. As a result, it’s apparent that a carefully-chosen collection of 100 or so individual trees can represent an enormous swath of available worldwide apple biodiversity. Deliberate grafting of multiple genetic individuals on each tree could fit them into a large suburban backyard.
We have used USDA’s Genetic Resources Information Network database to prioritize acquisition of individuals from the highly diverse core collections. With help from apple collector and breeder Don O’Shea of Ogdensburg, NY, who grafted trees for us this year, we now have about 50 of the necessary trees “in the ground” here in Boulder. We’ll continue to request additional apples from this diverse subset of USDA’s collection in coming years, doing the grafting ourselves now that we have gained the necessary skills. Eventually, we’ll build out our collection to include as many of the 100+ members of the diversity core collections as possible.
2015 M. sieversii scions on Antonovka rootstock in April, 2015. Starting small! (c) 2015, Eric Johnson
That’s when the real fun begins.
First, we plan to make clonal material from these trees available to others at low or no cost, so that more people can take advantage of and protect this priceless genetic material.
Second, as the trees in our own Malus sieversii orchard begin to bear fruit, we’ll collect seeds and distribute those, making it possible to distribute an entire collection of apple biodiversity, akin to our own, in a single padded mailer, for the cost of a couple dollars of postage.
Third, while I’m sure the wild trees will be lovely, and some will produce useable (if not commercially popular) fruit, we’ll start to make controlled crosses with domestic varieties. Our goal here will be to begin creating the apple varieties of the future … apples adapted to our local conditions and needs.
Many of the trees at Geneva have shown some resistance to fireblight, perhaps the most significant disease of apple trees in our area. Some of the individuals we plant locally will have a degree of fireblight resistance. We anticipate that some of their offspring will also have fireblight resistance. In the long term, the potential exists to develop disease-resistant varieties, reducing the need for expensive chemical disease controls.
We’ve actually already begun to distribute these wild apples in a somewhat less-organized way. As a result of its work being publicized in Michael Pollan’s Botany of Desire, USDA has made open-pollinated M. sieversii seed from its Geneva planting available to the general public. Labeled as to the identity of the mother tree, the pollen parents of these seeds are a mixed bag of whatever M. sieversii pollen the bees happened to be carrying around. We have grown out young trees from these seeds, using seed lots from eight mother trees. We have distributed more than 100 seedlings from the open-pollinated seed lots to interested parties, and have additional seedlings awaiting permanent planting locations.
Grafted Malus sieversii trees after a season of growth in the nursery, September 2015. Note the hail shield … a worthwhile precaution in our climate. (c) 2015, Eric Johnson
It’s important to note that most of the M. sieversii trees, and their immediate offspring, will not bear fruit marketable for fresh eating. In modern apple breeding programs, thousands of seedlings may be grown out to identify a single new variety for commercial production. However, for local culinary uses and smaller-scale production, a much larger fraction of seedlings may be acceptable. Others will bear fruit that may be made into preserves, or pressed and used in juice blends, fermented cider or vinegar. And in the long term, there is great potential for breeding high-quality varieties for fresh eating using a local M. sieversii collection.
Anyone with an apple tree, or enough space for one, can participate in this important work. The future of the apple can be created in our yards and gardens.