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DISEASE RESISTANCE IN COFFEE ‘AN ONGOING BATTLE’

DISEASE RESISTANCE IN COFFEE ‘AN ONGOING BATTLE’



World Coffee Research says fighting coffee leaf rust through genetic resistance via F1 hybrids ‘is an effective tactic’ but won’t be enough to protect farmers from significant crop losses

In a presentation at the 2018 ASIC event in Portland, Oregon, World Coffee Research Scientific Director Dr Christophe Montagnon said some coffee varieties’ rust resistance has begun breaking down, with the latest example being the Lempira variety from Honduras’ IHCAFE.

Dr Montagnon told attendees that researchers believe it is only a matter of time before rust resistance in most resistant varieties is going to break down, perhaps in as little as 5-10 years in many countries.

This development highlights the need for farmers to focus on plant health no matter the variety of their coffee.

Secondly, those traveling between origin countries must develop a heightened sensitivity and awareness for appropriate phytosanitary practices to prevent spreading fungi and other diseases from farm to farm or region to region.

Thirdly, the coffee industry needs to prioritize ongoing research and development. New sources of rust resistance can be found and must be discovered to foster sustainable coffee production.

Coffee’s scientific community, led by World Coffee Research in collaboration with coffee-producing countries, and with the support of the broader coffee industry, must seek to produce new solutions, new technology, and new ways of combating plant disease, Dr Montagnon said.

Highlighting plant health

A crucial part of rust-control strategies going forward, according to World Coffee Research and others in the scientific community, is the promotion of plant health in coffee production, which has been overlooked in the past.

Just as humans are more likely to be healthy if they exercise well and eat good food, coffee is better equipped to defend against rust when it is in good health. Factors contributing to plant health include good maintenance, soil conservation, adequate plant nutrition, and adequate shading.

A recent study from World Coffee Research and CIRAD recently showed that good fertilization can be as effective as spraying fungicide in protecting a genetically susceptible coffee against rust. Furthermore, it is acknowledged that one of the main reasons for the 2012 rust crisis in Central America was farmers’ reduced maintenance of their trees, itself due to low prices of coffee.

A plant’s health, or inherent vigour, is also dependent on the plant’s genetics and maintenance. F1 hybrids are inherently vigorous due to ‘hybrid vigour’ and benefit from their health in their ability to defend themselves against rust, even if they don’t bear the rust resistance genes.

For three years following the coffee leaf rust outbreak in 2012, the disease caused destruction in Central and South America. Many farms lost 50-80 per cent of their production, and the epidemic forced 1.7 million people out of work and drove human migration.

Once the rust outbreak hit, farmers who could afford to plant rust-resistant varieties did so, renovating areas of their farms with the new varieties. Combating diseases like rust is one action modern farmers must take to protect against the intensifying effects of climate change, which are evidenced in rising temperatures, unpredictable weather patterns, and higher rates of plant disease.

Resistance is waning

Unfortunately for some farmers who planted new varieties, no form of disease resistance lasts forever, as pathogens adapt and continue to attack coffee trees. As highlighted above, in 2017, IHCAFE announced that Lempira, one of the varieties it had bred, was no longer resistant to coffee leaf rust. Since 2013 the Centre for Research on Coffee Rust (CIFC) in Portugal has also observed varieties losing their rust resistance in different countries such as Brazil and India.

For the last 30 years, rust resistance has relied on the resistant genes coming from Timor Hybrid, a natural cross between Arabica and Robusta, but the hybrid’s resistance is breaking down.

“Rust resistance coming from different sources of introgression – that is, the transfer of genes from one species to another after hybridization and backcrossing – is being broken step by step,” said Dr Montagnon.

He explained that the introgressed varieties such as Catimors and Sarchimors that resisted rust for 30 years are no longer resistant.

New solutions being studied

Beyond promoting plant health, World Coffee Research is working on R&D to develop new solutions. These initiatives include continuing to search for new sources of resistance that could be used in breeding. This includes researching other species such as Robusta to see if there are ‘resistance traits’ that could be brought to Arabica through smart breeding.

Others include creating F1 hybrid varieties that are more tolerant to stress and have been shown to fare better against rust. New F1 hybrid varieties are currently in development and should be ready to be released to farmers by 2025.

The coffee research organisation is also learning more about coffee leaf rust and is working with renowned expert Mary Catherine Aime at Purdue University to explore the rust genome and genetic diversity, decipher its mutation ability, and potentially find solutions to mitigate it.

WCR is also studying coffee profitability through its Global Coffee Monitoring Programme in order to research ways to reduce cost of production for farmers while maintaining plant health and vigour so that coffee is more profitable for them.

At the same time, it is exploring new solutions such as biocontrol, making use of micro-organisms that either attack rust infections or protect the coffee plant against infection and says it has promising results that it hopes to validate. It is also warning against the practice of moving plant material (such as seeds) around countries or continents, which spreads coffee leaf rust and other diseases. Phytosanitary regulations are made to ensure safe movements of plant materials – if the spread of diseases can be slowed by even a few years, it will give scientists the ability to meet the challenge with improved varieties, agronomic practices, and treatments.

Collaboration needed

World Coffee Research may be the coffee industry’s leading research and development organization, but it cannot solve the complex problem of plant disease on its own and works hand in hand with over 25 coffee-producing countries and advanced research institutes. These partnerships ensure that research reaches farmers’ fields rather than remaining in the lab.

“The situation is urgent,” said founder and CEO, Tim Schilling. “Coffee producers deserve the same tools and information that modern, profitable farmers have in the rest of the world. With further collaboration from companies throughout the coffee industry, we will develop and deliver coffee R&D solutions, from rust resistance to breeding and beyond, to farmers around the world. There is a role for each and every coffee company. This work is too big for any one company to achieve, but together we will help farmers maintain and improve their livelihoods.”■ C&CI

Fertilizing, spraying and shade

Work carried out by World Coffee Research in Central America with Dr Jacques Avelino has come to some interesting conclusions about whether it is more beneficial to spray coffee trees to prevent leaf rust or provide them with better nutrition. The research has also looked in detail at how rust interacts with coffee microclimates, different management practices, and the coffee plant itself.
Dr Avelino’s work looked at the interaction between altitude and two main approaches to crop management – fertilization and spraying fungicides – on the severity and growth of coffee leaf rust infections. What is better for the coffee plant: to spray against rust, or to give the plant better nutrition to allow it to grow strongly and as a result fight rust? And how does this answer change with altitude?
The study demonstrated that at lower altitudes, where rust thrives, high levels of fungicide application are not very effective at controlling rust. The effectiveness of fungicide increases as altitude increases. However, plant nutrition contributes to low levels of infection regardless of altitude.
Clear, rigorous data from working farms seems to show that fertilization enhances the plant’s physiological response in fighting the growth of rust lesions, and that at low altitudes where rust thrives, applying fertilizer was more effective at controlling rust than spraying with fungicide.
Common sense would tell you that a healthy, well-fed plant is better able to fight off infections. However, no hard facts or rigorous studies have previously proven this assumption. World Coffee Research said the findings are especially important given that the fungus seems to be overcoming rust-resistant varieties, as has happened with the Lempira variety in Honduras.
Another study led by Dr Avelino looked at shade and the possibility that certain types of shade reduce the intensity of coffee leaf rust infection.
“Many existing approaches for controlling coffee leaf rust are one-sided,” said the organisation. “Use rust-resistant varieties, or spray with as much fungicide as you can afford. But it is increasingly evident that we need to open new fronts in the fight against coffee leaf rust. To do so, we need better science on how rust interacts with coffee microclimates, different management practices, and the coffee plant itself.” Dr Avelino published a study in 2017, adding an essential understanding of how coffee leaf rust interacts with coffee, providing insights into how it can be controlled.
Research suggests that some types of shade may actually make coffee leaf rust worse, despite being an important practice for coffee growers amid rising global temperatures. In general, there is more coffee leaf rust under shade than on plants grown in full sun. However, shade-grown coffee is typically better able to defend itself against a rust infection because shaded trees are not as stressed as full-sun trees. And clearly shade is necessary to cope with climate change – abandoning shade entirely is not a viable approach to managing coffee leaf rust.
Dr Avelino conducted a study for World Coffee Research at CATIE in Turrialba, Costa Rica, to determine whether there are approaches to reduce the negative effects of shade without diminishing the positive effects. The team concluded that shade tree species that increase the so-called ‘washout’ of coffee leaf rust spores (the gentle washing of spores off leaves to the ground, without spreading the spores) would help to reduce the intensity of coffee leaf rust infections.
This points to an intriguing conclusion, that some types of shade tree may be better than others for controlling coffee leaf rust outbreaks. Small shade trees with small, flexible, lobbed leaves, or easily manageable shade trees that enable high shade cover in the dry season and low shade cover during the rainy season, are of interest for that purpose. ■ C&CI

 

Reuniting coffee leaf rust with its natural enemies

Expensive fungicides and pesticides aren’t the only way to control pests and diseases on a farm. Left to its own devices, nature has developed complex and effective ways of reducing damage by diseases. Natural control exists because every organism in nature has a range of natural enemies – competitors, parasites or predators – that are capable of reducing the size of its population. In the wild, coffee leaf rust has its own range of natural enemies.
When coffee and coffee leaf rust were removed from their place of evolutionary origin in Africa and began to be cultivated in new environments, rust was able to thrive and become more aggressive because it had left behind its natural enemies. Classical biological control reunites pests with their natural enemies.
Two types of fungi are known to be particularly important for coffee leaf rust. Fungi that ‘eat’ other fungi such as coffee leaf rust are called mycoparasitic fungi. Other organisms, capable of living inside the tissue of the coffee plant and working as bodyguards, protecting the plant against attacks by diseases and pests like rust, are called endophytic organisms.
Both types of beneficial organisms might be exploited on coffee farms as organic control products or sustainable tools for managing coffee leaf rust, and WCR is working with researchers Robert Barreto and Harry Evans at Universidade Federal de Viçosa in Brazil to identify and evaluate such organisms to be used in the fight against coffee leaf rust.
Right now, the research continues with detailed evaluation of the physiological effect of promising mycoparasitic fungi on coffee leaf rust infection, disease development and plant health, as well as testing the beneficial impact of endophytic organisms in promoting healthy coffee plants and drought resistance.
■ C&CI

This article first appeared in the November’18 issue of C&CI, click on subscribe now if you wish to read other informative articles in the November and future issues of C&CI.

 

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