last objection is the most compelling one against an early introduction of the rust to Ceylon: if the fungus had been present on the island for any significant length of time, why didn’t the epidemic break out sooner? All the ecological conditions for a large-scale rust epidemic had existed since at least the coffee craze of the 1840s. One possibility is that the fungus had been present in Ceylon for some time, but the arabica plants cultivated in Ceylon were resistant to the strain of H. vastatrix that was initially introduced. After a time, a new, more virulent strain of the fungus evolved that could overcome that resistance. Later in the story, we shall see examples of this pattern. But as far as we know, most cultivated arabica is susceptible (to a greater or lesser degree) to all strains of H. vastatrix, and many, if not most, plants would surely have shown at least some lesions. It is hard to understand how it could have escaped notice altogether before 1869.
The location and pattern of the early rust outbreak in Ceylon strongly suggest that the rust was introduced. It began at a single point—Madulsima—in the interior of the island and spread outward from there. This pattern is characteristic of what plant pathologists now call a “focal epidemic,” which typically begins with a low level of inoculum (in this case, spores) at a well-defined location. The fungus then spreads outward from the focus in waves, like ripples in a quiet pond after a stone is dropped in.8 Had the fungus already been widespread in Ceylon’s forests, it is highly unlikely that the disease would have appeared at such a well-defined location; the epidemic would have been generalized across Ceylon’s coffee farms from the very beginning. But if we accept that the fungus was introduced, then we need to ask how.
In the mid-nineteenth century, pathogens of all kinds were traveling farther and faster than ever before. The historian David Arnold has aptly described the Indian Ocean basin in those years as a “disease zone” in which pathogens of all kinds followed the ebbs and flows of empire and found new host populations on which to survive and reproduce.9 Ceylon was tightly linked into a global network of steamships that regularly and swiftly moved goods and people between Asia, Africa, the Pacific, and beyond. New innovations like the Wardian case—essentially a portable greenhouse—made it possible for people to ship live plants anywhere in the world.10 This increased the risk of accidentally moving diseases and pests that fed on those plants. Newly empowered public institutions, such as the Royal Botanic Gardens at Kew, helped broker the movement of plants and seeds across the global tropics. Private nurseries, such as William Bull and Sons in London and the Horticole Coloniale in Brussels, also supported a global trade in tropical seeds and plants. The geographic and economic barriers that had for several centuries kept the coffee rust contained in Africa had begun to erode.
In the 1980s, the biologist Gordon Wrigley speculated that the spore might have been brought to Ceylon by the Napier expedition, a military expedition that sent troops from India to Ethiopia early in 1868. While in Ethiopia, the expedition passed through a number of minor coffee-growing areas where the rust may have been present. A number of people on the expedition, including Napier himself, had close connections with Ceylon. Wrigley speculates that they “might have returned with some live or pressed coffee plant material carrying viable spores.”11 This is one possible explanation. But the fungus need not have come from Ethiopia; it was also present on wild coffees in the Great Lakes region of East Africa and in the upper reaches of the Congo. Trade routes for slaves and ivory passed through these regions. These routes linked the East African interior to maritime trade networks spanning the Indian Ocean and beyond. They were heavily traveled by many people, including African slaves, Arab traders, and European missionaries and explorers, among others. Perhaps one of these travelers brushed up against some infected coffee plants and inadvertently picked up some spores on his or her clothing. Then, that person may have gone to Ceylon and inadvertently brushed up against an arabica plant, leaving some spores on the susceptible arabicas. The specifics of how the fungus got from eastern Africa to Ceylon are unknown, and likely unknowable. But the circumstantial case is clear: one way or another, the rust epidemic was triggered by intensifying connections between the interior of East Africa and the Indian Ocean.12 Taken individually, any given transfer between East Africa and Ceylon was unlikely. But taken together, as ever more people and goods were moving from Africa to Ceylon, there was a greater likelihood that some rust spores stowed away on a journey.
Of course, the spore was just one part of the story. The epidemic in Ceylon was devastating because the island’s coffee estates provided the fungus with the ideal conditions in which to reproduce. The outbreak was abetted by Ceylon’s climate. The rains that accompanied Ceylon’s two annual monsoons showered the coffee plants, providing ample supplies of the water droplets that the fungus needed to germinate. Ceylon’s comparatively warm temperatures, especially at lower elevations, also helped the spores reproduce. During a single crop season, the fungus could easily complete several infection cycles. In Ceylon’s warm and wet landscapes, much of inoculum survived from one crop season to the next, reinfecting each new crop of coffee. The coffee estates presented few physical or genetic barriers to prevent rust spores from dispersing and reproducing. The intense monsoonal winds—largely unchecked by forest trees or shelter belts—dispersed spores widely across the island. In this context, a vastly greater proportion of the spores released by each lesion landed on susceptible coffee plants, colonized their leaf tissue, and produced new lesions that, in turn, liberated countless new spores of their own.13 The outbreak in Ceylon was the fungal equivalent of nuclear fission. Just fifteen years after the rust was first detected in Ceylon, the island’s once-vibrant coffee industry had collapsed.
Competing Models of Crop Disease
Farmers and scientists alike struggled to make sense of the disease. Crop diseases on this scale were new; the potato blight in Ireland, for instance, had taken place just two decades before. And the coffee rust developed in complicated ways, making it difficult to read. In some years, it seemed far less severe than in others. During the initial attack, “the trees were denuded of their leaves altogether, and the site is then so pitiable that during the early years of the attack experienced planters recommended the abandonment of fields.”14 But the defoliation was not permanent. A few months after the initial defoliation, the trees “had put on a fresh flush of leaves and were bearing several hundredweights of crop per acre.”15 It seemed, at least initially, that the disease afflicted European estates more severely than the farms of Sinhalese coffee planters. “The coffee and plantations and gardens cultivated on the European system seemed likely to suffer most,” wrote one government official, “while much of the unpruned coffee surrounding the villagers’ huts and houses presented a fair show of berry.”16
Scientists quickly started searching for explanations and solutions. The farmer who first encountered the disease took some infected coffee leaves to the director of the Royal Botanical Gardens at Peradeniya, George Thwaites. The garden, located near Kandy in the heart of Ceylon’s coffee country, was then one of the world’s leading tropical botanical gardens. Nonetheless, naturalists at the garden had conducted little research on coffee agriculture. The garden’s applied research focused on acclimating exotic crops such as cinchona and tea.17 Thwaites had spent more than two decades studying Ceylon’s flora, but he had never encountered anything like the rust. So he sent the leaves back to Joseph Hooker at the Royal Botanic Gardens of Kew in England.
Hooker immediately forwarded the infected leaves to Miles Berkeley, Great Britain’s leading plant pathologist. Two decades earlier, Berkeley had participated in the commission to study the causes of the Irish potato blight (Phytophthora infestans). His research on the potato blight convinced him of fungal pathogenicity, a view of plant diseases that was, for the time, quite new. In the 1850s, he had published extensively on crop diseases.18 Berkeley had begun his scientific career as a specialist on the fungi of Great Britain, but he also developed an expertise in tropical fungi collections from British expeditions around the world, including the voyages of Darwin’s Beagle. He had previously analyzed the thousands of fungi that Thwaites collected in Ceylon.19 Given his expertise on crop diseases and his deep knowledge of Ceylon’s fungi, it is difficult to imagine anyone better suited
