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PORTLAND OR, USA – A new study that involved the unprecedented collaboration of coffee researchers and collaborators from 15 countries at 23 sites around the world provides insights into how 29 Coffea arabica varieties respond to coffee leaf rust (CLR), a devastating disease affecting coffee crops worldwide, reports the World Coffee Research on its website. Varieties respond differently to disease and this research, published in Frontiers in Plant Science, is the most extensive evaluation of arabica coffee varieties under diverse environmental conditions to date.
“No single country or institution can solve the complex challenges facing coffee on its own,” says Dr. Tania Humphrey, the scientific director of World Coffee Research.
“This trial shows the power of global collaboration—by pooling data, expertise, and resources across continents, we’re able to generate insights that no single program could uncover alone. It’s a model not just for coffee, but for how agricultural science must evolve to meet the demands of a changing world.”
Genetic armor: rust resistance isn’t one-size-fits-all
Utilizing coffee varieties resistant to rust is among the most sustainable and cost-effective strategies for farmers to minimize economic losses from the disease. Resistance depends on the genetic makeup of both the coffee plant and the pathogen. To date, over 55 races of CLR have been identified, each interacting differently with various coffee varieties.
Arabica coffee’s resistance genes, known as SH genes, have been sourced from different species: SH1, SH2, SH4, and SH5 from C. arabica; SH3 from C. liberica; and SH6 through SH9 from C. canephora (via Timor hybrids). Commercial arabica varieties often contain combinations of these genes, but no single variety has all the known resistance genes. Moreover, the pathogen’s continuous evolution necessitates ongoing efforts to identify and integrate new sources of resistance.
“Understanding rust can be complex for farmers. By identifying which varieties really work against rust in real-world conditions, this research gives farmers better tools to sustain their crops, their incomes, their dignified life, and their future,” says Albertino Meza Ojedas, Agricultural Research Manager at CENFROCAFE. The Peruvian cooperative represents 2,800 coffee-growing families and hosted one of the global network sites. “It’s an honor to participate in this global study that brings together scientists from around the world to solve a shared problem.”
Coffee leaf rust: One global trial, 18 countries, 31 varieties
In 2015, the International Multilocation Variety Trial (IMLVT) was established by World Coffee Research, together with partner institutions around the world. The trial placed 31 arabica coffee varieties from 11 breeding programs worldwide into 29 research plots in 18 countries. Importantly, the trial sites captured a huge diversity of climatic conditions, from hot and dry sites in Zambia to cooler, wetter sites in places like Gambung in Indonesia. This unprecedented global effort aimed, in part, to assess natural coffee leaf rust infections under real-world field conditions. For the rust study, a subset of data from the global trial network was analyzed, based on data availability and quality. (Data from 23 of the 29 original sites, in 15 of the 18 network countries, was used; performance of 29 of the 31 varieties was analyzed.)
Global best-bets and local champions
While some varieties exhibited high resistance across multiple sites, none were entirely immune, and all showed some susceptibility in certain locations.
Some varieties, like Parainema, Kartila 1, and IPR107, offered a promising balance of high resistance to coffee leaf rust and stable performance across environments, making them good all-around choices for rust resistance. Others, like EC16 and Catigua MG2, showed very high resistance in some locations, but weren’t as high-performing in others (i.e., their performance was not as “stable” across sites). These varieties perform best under specific conditions. Varieties with pure arabica backgrounds generally showed higher susceptibility, whereas those with interspecific introgressions, such as Timor hybrid derivatives, exhibited greater resistance.
The study highlights the need for continuous monitoring and adaptation to evolving disease pressures.
