increased production would offset the costs incurred by disease control. Now, even in conventional coffee production, control programs focus more on ecological and economic sustainability. Both the ecological and economic challenges must be addressed if coffee is to have a long-term future.
CHAPTER 2
Coffee Rust Contained
HISTORIES OF epidemic disease often begin with a dramatic story of the first outbreak and the chaos it produced. While this approach makes for a compelling beginning, it also privileges the pathogen’s role in the disease. It diminishes, and sometimes erases, the critical role played by the other two elements of the disease triangle. Shifting focus to these other elements—in this case, the coffee plant and the ecosystems—reminds us that epidemics do not appear out of nowhere. Rather, epidemics are fundamentally historical; they are the product of long-term processes that produce vulnerable ecosystems. Here, we will follow arabica coffee’s journey around the world, in a series of transfers that took it from a small corner of southwestern Ethiopia across the global tropics, while leaving the rust fungus behind. We will track how political and economic forces—especially but not only European colonialism—shaped coffee’s growing popularity as a crop and as a drink. As coffee became more popular, farmers continued to expand coffee frontiers, which consisted almost exclusively of rust-susceptible arabica cultivars. They also intensified coffee production. By the mid-nineteenth century, the world’s coffeelands produced more coffee than ever, but they were also more vulnerable to diseases and pests. Productivity and vulnerability were, at that moment, two sides of the same coin.
The coffee that most of us drink is known botanically as Coffea arabica. The plant belongs to the genus Coffea, which includes more than one hundred species. Species of Coffea grow in a wide range of ecosystems across equatorial Africa, from dry lowlands to wet highlands, and from Liberia in the west to Madagascar in the east (see map 2.1). Arabica coffee, however, is native to one small corner of this range: the montane forests of southwestern Ethiopia, west of the Great Rift valley, between 1,300 and 2,000 meters above sea level in the regions of Kaffa and Illubabor. It enjoys the temperate highland climates, growing best in the shaded, diverse under-story of the forest canopy with temperatures between 15°C and 28°C and moderate amounts of rain.1 It is a small woody tree, like a shrub, that usually has one main stem with lateral branches growing almost horizontally. The branches are densely covered with dark green leaves, which the plant retains year-round. It produces fruit: the coffee “cherries.” The coffee we drink is made out of the dried and roasted seeds of this fruit (see fig. 2.1). “When man does not interfere,” wrote the coffee expert Pierre Sylvain, “the forest is quite dark and the coffee trees are spindly; they reach considerable height but produce only enough fruit to ensure the survival of the species.”2
Map 2.1. Distribution of coffee species in the wild. (From Maurin et al., “Towards a Phylogeny for Coffea,” 1571)
Figure 2.1. Coffee branch and berries. (In Thurber, Coffee, frontispiece)
Genetically, the arabica coffee plant differs from other Coffea species in one significant way. It is self-fertile (autogamous), meaning that only one parent plant is necessary to flower and produce seeds. All other species of Coffea are allogamous, requiring two parents to flower and produce seeds. Arabica’s distinctive genetic makeup made it suitable for transplant over great distances, since only a single plant (or seed) was necessary to establish a new population.3 It also meant that populations of arabica tended to be homogeneous, which, as we shall see, could be environmentally risky but commercially desirable. Arabica’s self-fertility made it easy for farmers to produce a consistent product from one harvest to the next. These advantages came at a price, however. Arabica coffee is also less genetically variable than other coffee species, leaving it susceptible to diseases and pests.4
One of these is the coffee leaf rust, caused by the coffee rust fungus known scientifically as Hemileia vastatrix. It is an obligate parasite of coffee; that is, it can only complete its life cycle on plants of the genus Coffea. The fungus begins its life cycle as a tiny spore. The spore will only germinate in specific conditions: it must be deposited on the underside of a coffee leaf, the air temperature must be 15°C–28°C (optimally 21°C–25°C), and water droplets must be present on the underside of the leaf. A coffee writer in the 1920s aptly described fungi like H. vastatrix as the “vampires of the vegetable world” since they feed on the tissue of other organisms. Once H. vastatrix germinates, it penetrates the leaf and sends shoots into the leaf tissue. The fungus creates a branching mycelium that feeds on the surrounding leaf tissue, forming circular orange pustules. Ultimately, these shoots produce spore buds that pierce back out through the underside of the leaf. Each pustule can contain as many as one hundred thousand spores, each of which can begin the infection cycle anew (see fig. 2.2). The spores can be dispersed by winds and rain, or by the many insects, animals, and people that pass through the ecosystem. During a severe rust outbreak, rust pustules can cover the coffee leaves, causing them to fall prematurely. Defoliation deprives the coffee plants of vital nutrients. Repeated infections debilitate the plant, preventing the branches and fruit from developing fully.5
The precise geographic distribution of H. vastatrix in the wild remains unclear. The coffee expert Albertus Eskes argues that “it is most likely that H. vastatrix has coevolved simultaneously on many coffee species from all over Africa.”6 In principle, the geographic range of H. vastatrix in the wild could have been as large as the range of the Coffea genus. But some fragmentary historical evidence, discussed in later chapters, suggests that H. vastatrix’s wild range spanned the Great Lakes region and Ethiopia in East Africa, as well as the eastern half of the Congo River basin. The genetics of the coffee plant and the fungus also offer clues about the fungus’s historical distribution. The fungus has evolved into strains (physiological “races”) that specialize in attacking particular species of coffee. Most Coffea species, in turn, have developed some degree of resistance to the fungus. The most highly rust-resistant species, such as C. canephora, grew in warm and humid areas favorable to the fungus. The least rust-resistant species, including C. arabica, grew in cooler and drier areas that were less hospitable to the fungus.7 The presence of resistant genes in each coffee species therefore offers clues to the presence of the rust in its habitat.
Figure 2.2. Coffee rust infection process, simplified. A. Rust spores are disseminated by wind, humans, rain splash, insects, and animals. B. Spores are deposited on healthy coffee leaf. C. Spores germinate and infect leaf tissue, producing characteristic orange-colored lesions on the leaf. D. Infection causes premature leaf fall. E. Cross-section of infected leaf, showing how fungus colonizes leaf tissue and then sporulates, beginning the infection process anew. (Illustration by Angel Luis Viloria Petit)
Although H. vastatrix was widely distributed across Africa, serious outbreaks were unknown. “The available information,” writes Eskes, “suggests that most African coffee species have developed a balanced relationship with H. vastatrix, showing generally little disease under natural conditions.”8 Both the historical and genetic records suggest that the rust fungus was widespread in the wild home of arabica coffee, yet it is unlikely that there was ever a major outbreak there. Wild arabica, like other coffee species, developed ways of coexisting with the rust. All arabica varieties have some degree of resistance,
