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maize, soy, and rice have 20–30 percent diversity. It appears as if Arabica coffee is one of the least genetically diverse crops in the world. That said, there is still no definitive answer about the amount of diversity Arabica possesses because we haven't tested all Arabica coffees. There are forests in Ethiopia that contain wild coffee that just may be an untapped reservoir of genetic diversity. W h y i s i t s o l a c k i n g i n d i v e r s i t y ? Why is it so lacking in diversity? Imagine a funnel—big at the top, with only a pinprick opening at the bottom. At the top, put in all the Arabica coffee in existence, prob- ably a few thousand varieties (in reality, there is no definitive num- ber). After a series of "constriction events" that trace the history of coffee as it leaves wild forests, becomes domesticated on farms, and travels around the world on colonial trade routes, what you get out of the bottom of the funnel is a small handful of the main varieties that are grown widely today. The history of coffee is visible in its genetic diversity. The first major constriction happened when Arabica itself was created, which scientists think happened in a forest in Ethiopia about 10,000 years ago. It was a serendipitous one-night stand between (sci- entists think) C. canephora and C. eugenioides. The fact that it was a one-time-only event is one reason Arabica has limited genetic diver- sity. Another major constriction occurred when Arabica was taken from Ethiopian forests and domesticated on farms in Yemen between 850 and 1300 A.D. In Yemen, coffee became part of the Arabian trade route and came to the attention of Europeans in 1615. A century later, the Dutch, French, and British became interested in coffee as a tropical cash crop that could be established in colonial outposts. It's thought that only a small handful of coffee plants of two types— Bourbon and Typica—became the basis for nearly all coffee planted in the New World throughout the 1800s and 1900s. And the Arabica cul- tivation in most of the world today is thought to contain a tiny fraction of the total genetic diversity possible in the species, which isn't much. W h a t c a n w e d o a b o u t i t ? What can we do about it? Coffee scientists are extremely interested in trying to increase the genetic diversity of Arabica—not in the species as a whole, but in the varieties most commonly cultivated. It turns out this is not terribly hard to do, if you have the right tools. Until about 1960, coffee breeders had only one main strategy for developing new varieties: selection. They would take an existing variety, watch for a desired trait—like the ability to produce more cherries—and select only the beans from the highest-producing plants. The problem is that the varieties they began with—derivatives of Bourbon and Typica—were extremely genetically narrow from the start. Where do scientists turn to find varieties with more genetic diversi- ty? One critical source is forest and garden coffee from coffee's center of origin, Ethiopia. Unfortunately, forests in Ethiopia are disappear- ing at an alarming rate. The United Nations estimates that 40 percent of the country was once covered in forests; today it's 3 percent. Some predictions estimate they will by gone by 2020. Many organizations have done work to protect critical forest reserves, like the Kafa Biosphere Reserve, but they are still vulnerable. It's possible—and indeed likely—that much of the genetic diversity that once existed in Ethiopia's forests has already been lost. In the 1960s, however, multiple scientific missions went to Ethiopia to collect coffee for exactly this reason. In all, nearly 1,000 Ethiopian coffees—some wild, some from farms—were amassed and sent to sci- entific research stations, where they became living germplasm collec- tion. (It should be noted that Ethiopia was never compensated for the removal of their varieties on 20th-century collecting missions, which is one reason why the country today does not allow anyone to remove this biological resource and make use if it outside the country.) A germplasm collection is basically a library of coffee's genetic diversity, except instead of books, the library is made up of plants. Coffee breeders go to this library any time they want to create a new variety—perhaps something resistant to a particular disease, or one that grows small so it can be planted tightly together, or one that is well adapted for sunny or shady conditions. The latter will be increasingly important in the coming decades, because shade trees act as carbon sinks and can cool ambient temperatures by two-to-three degrees, simultaneously mitigating climate change and creating con- ditions for higher-quality coffees. In the past, breeders could only characterize the plants in a germ- plasm collection roughly based on how they looked and by what diseases they were susceptible to. The plants, or "books," in the library were clearly distinct, but the pages had few or no words on them. Now, however, new technology is allowing scientists to quickly and dramat- ically increase their understanding of these varieties, for example, to identify particular genes and genetic markers linked to traits that will be important in the 21st century, like drought tolerance, quality, and disease resistance. The pages are becoming more legible. This allows scientists to make more informed decisions about which varieties are likely to have the traits they are looking for, instead of making guess- es that take 20–30 years to validate. To increase the genetic diversity of Arabica, you need to mate two different varieties together, preferably two that are genetically distant. With new genetic sequencing technologies, it's possible to analyze a large number of varieties and determine their "genetic dis- tance" from one another. Once you know this, you can select geneti- cally distant plants and cross them together. In 2015, WCR sequenced the 100 most diverse Arabica varieties from a collection of 846 plants from the CATIE germplasm collection in Costa Rica, and is using them to create experimental varieties that will be tested in the field within five years. Many of the world's coffee germplasm collections are in disrepair now, but they are still the main source of diversity available to coffee breeders around the world. Though they have existed for decades, most of the material in them hasn't been used in coffee breeding until recently. In the long run, to significantly increase Arabica's genetic diversity, scientists may need to turn to other coffee species besides Arabica. Robusta, for example, is significantly more genetically diverse than Arabica, which is one reason it is able to tolerate diseases and pests more effectively, and why it can be grown in a wider range of climates. Coffee breeders have already tapped Robusta for one important trait: resistance to coffee-leaf rust. A whole group of varieties with Robusta genes (commonly referred to as Catimors and Sarchimors; Robusta was a grandparent of these varieties) was created in the last half of the 20th century as leaf rust became a major problem in Latin America. In the future, it may be possible to isolate important genes from Robusta that could help Arabica withstand other diseases or rising temperatures, without some of the negative flavors that are often associated with Robusta genetics. It might also be possible to try to "re-create" Arabica by attempting controlled crosses of Arabica's original parents, C. canephora and C. eugenioides. Standing in my kitchen hand-washing my grandmother's china after my own private variety tasting, I thought about what I'd just experi- enced. On the one hand, the kind of tasting I'd just experienced is still 86 barista magazine