May 2013 C&CI • Disease & Pest Control • 41
scientists can give farmers any warning of a future outbreak? How much extra will it cost to protect the crop against future outbreaks, he asked, and what is the relationship to shade? “Our recent surveys there find that both sun and shade coffee plots have been heavily infested,” he said.
Breeding strategies CABI scientist Harry Evans is working on
rust genetics with Robert Barreto’s group at Viçosa University in Brazil (see C&CI ‘What the Papers Say’ March 2012). They have discovered that the rust can produce sexually, something that was previously considered impossible. This may have profound effects on the breeding strategy for future rust-resistant varieties. World Coffee Research, which was due to host the April meeting of experts in the fields, said it believes that climate change is responsible for the outbreak of coffee leaf rust disease. In a statement, WCR said: “Many coffee farmers across Central America will not turn a profit in 2013 and some will even go out of business due largely to the near-epidemic levels of coffee rust disease.” “Poor harvests and low market prices this year will deal a lethal blow to many marginal coffee farmers,” said Dr Tim Schilling, Executive Director of WCR, at the Borlaug Institute of International Agriculture at Texas A&M University.
“This year turns out to be the perfect storm for coffee rust in Central America,” said Dr Benoit Bertrand, a scientist at CIRAD, the French development agency that works with tropical crops. High levels of rust spore populations were left on the ground from last year and heavy rainfall allowed the disease to multiply and rapidly attack coffee plant leaves, reducing the plant’s ability to produce. “In some cases, coffee trees have lost all their leaves, branches have withered completely, sometimes killing off the tree,” Dr Bertrand said.
Dr Schilling said what he called “wild and extreme climate events like this” will continue and cause more problems in future. “We simply must invest in research to provide solutions to farmers while governments and the UN try to fix the global climate crisis.”
Dr Bertrand said that although there has been speculation that the severe outbreak of rust this year was due to a virulent ‘mutant’ race, Cenicafé’s work has proved that this theory is invalid. “This year’s rust outbreak is not a new strain of the disease, but the same ‘RACE II’ of H. vastatrix commonly associated with rust damage in coffee around the world,” Dr Bertrand said. “The outbreak can be credited to this year’s
high continued rainfall.”
As to how to deal with future outbreaks, Dr Bertrand said: “Although the application of fungicides can be effective in the short term, it is nevertheless expensive, laborious, and environmentally unsound.” In his view, the best way to protect against rust in the medium and longer terms is through the use of a resistant variety of coffee. The good news is that resistant varieties do exist and even some of the new F1 Hybrids from different sources possess rust resistance combined with other desirable agronomic traits.
A coffee tree that has been defoliated due to coffee rust (courtesy: PLoS ONE)
Changed
Emma Bladyka, Coffee Science Manager at the Specialty Coffee Association of America, said warming temperatures at higher altitudes and the resulting shifts in moisture accumulation are allowing the rust to thrive in new areas. “The case of leaf rust is an example of how changing patterns of, rather than the total annual amount of precipitation, can really alter an ecosystem. Disruptions in the typical dry season can create an environment more habitable for rust outbreaks. Smaller and more frequent rainfall in the region likely contributed to the perfect fungal habitat. “The truth is that since there is not yet a full understanding of the biology of this fungus it is impossible to understand what exactly could affect its growth and proliferation, let alone how to eradicate it. This seems to be another example of where the scientific research on coffee is sadly lagging behind that of other crops,” she said. “There is no quick solution to this problem. The outbreaks have already occurred, and are known to proliferate into multi-year events. The usual means of keeping the fungus at bay are no longer solutions to the problem. Copper- based fungicides are most common, but have short periods of effectiveness and applications must be timed carefully. In the end, these metallic fungicides can be detrimental to the environment and are limited in capacity to combat coffee rust.” Currently, Catimors and Icatu show partial resistance to the rust, but lack many of the taste attributes desired by specialty coffee buyers. n C&CI
cultivation practices Although the extent to which reduced shade cover can influence an outbreak of coffee leaf rust is debated, some scientists firmly believe that a shift away from traditional coffee growing techniques may be increasing the severity of the outbreak. Professor John Vandermeer, a University of Michigan ecologist who studies the disease, has been running research plots at an organic coffee plantation in southern Chiapas, Mexico, for about 15 years. He and colleague Ivette Perfecto of the U-M School of Natural Resources and Environment (SNRE) study the complex web of interactions between resident organisms there, including various insects, fungi, birds and bats. Dr Vandermeer said more than 60 per cent of the trees on his study plots now have at least 80 per cent defoliation due to coffee rust; around 30 per cent of the trees have no leaves at all, and nearly 10 per cent have died. “I have personal reports from friends who work in coffee in Colombia, Costa Rica, El Salvador, Guatemala, Nicaragua and Mexico. They all say that it’s the worst case of the disease they’ve ever seen,” said Professor Vandermeer.
As he noted, over the last 20-25 years, many
Latin American coffee farmers have abandoned traditional shade-growing techniques, in which the plants are grown beneath a diverse canopy of trees. In an effort to increase production, much of the acreage has been converted to ‘sun coffee.’ Professor Vandermeer said he suspects that the shift to sun coffee may be contributing to the severity of the latest coffee rust outbreak. “The move to sun coffee results in a gradual breakdown of the complex ecological web found on shade plantations. One element of that web is the white halo fungus, which attacks insects and also helps keep coffee rust fungus in check,” he explained. “Both the widespread use of pesticides and fungicides and the low level of biodiversity found at sun coffee plantations have likely contributed to the decline of white halo fungus in recent years. Without white halo fungus to restrain it, coffee rust has been able to ravage coffee plantations from Colombia to Mexico.”
“What we feel has been happening is that gradually the integrity of this once-complicated ecosystem has been slowly breaking down, which is what happens when you try to grow coffee like corn,” Professor Vandermeer told C&CI. “This year it seems to have hit a tipping point, where the various things that are antagonistic to the roya in a complex ecosystem have declined to the point where the disease can escape from them. It could be that the disease is going to run itself out this year and will then return to previous levels, or it could be that it now becomes a relatively permanent fixture in the region.”
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