Coffee Rust Knows No Borders: Global Study Reveals How Environment and Genetics Interact in Arabica Resistance

In an ambitious feat of scientific collaboration, World Coffee Research (WCR) and an extensive network of global partners have released the most expansive field-based evaluation of Coffea arabica varietal resistance to coffee leaf rust (CLR) in history. Published in Frontiers in Plant Science, the study represents a turning point in how the world understands the interplay between coffee genetics and diverse agroecological environments. More than just an academic endeavor, this research brings critical, field-tested knowledge directly into the hands of farmers and breeders around the globe.

Spanning 15 countries, 23 research sites, and 29 coffee varieties, the International Multilocation Variety Trial (IMLVT) was designed to tackle the mounting challenge of CLR—a fungal disease that has haunted coffee farms for more than a century. Caused by Hemileia vastatrix, CLR threatens the economic sustainability of coffee-growing communities across Latin America, Africa, and Asia, with estimated yield losses between 35% and 75% during severe outbreaks.

Dr. Tania Humphrey, Scientific Director of WCR, emphasized the urgency and significance of the trial: “No single country or institution can solve the complex challenges facing coffee on its own. This trial demonstrates the power of global collaboration. By pooling data, expertise, and resources, we’ve produced insights that no single country could have achieved in isolation.”

Understanding the Scope and Impact of Coffee Leaf Rust

Coffee leaf rust is not a new phenomenon. Since its first documentation in commercial coffee in Sri Lanka in 1869, the pathogen has marched steadily across coffee-growing regions. It reached Latin America in the 1970s and made its most recent jump to Hawaii in 2020. Its ability to adapt and evolve means traditional containment methods such as fungicides and shading are insufficient in the long term.

With over 55 known physiological races of H. vastatrix, resistance to rust is increasingly seen as a moving target. Arabica coffee’s resistance genes—designated SH1 through SH9—have been introgressed from wild coffee species like C. canephora and C. liberica into commercial varieties. But these genes alone cannot outpace a pathogen that continues to evolve in complexity and virulence.

The IMLVT: A Landmark in Coffee Research

Launched in 2015, the IMLVT program was designed to identify the best-performing Arabica varieties in real-world conditions. The trials incorporated varieties from 11 breeding programs across diverse agroclimatic zones, from the dry, high-altitude plains of Zambia to the wet, shaded plantations in Indonesia.

Of the 31 varieties originally included, 29 were ultimately analyzed based on data integrity from 23 viable research sites. The trial allowed researchers to identify both globally stable performers and those suited to specific local conditions. Importantly, the research accounted for genotype-by-environment (GxE) interactions, confirming that a coffee plant’s resistance to rust is not determined solely by its DNA, but also by where and how it is grown.

Dr. Jorge C. Berny Mier y Teran, WCR’s lead scientist on the study, noted: “This is more than a rust resistance trial—it’s a foundational step toward smarter breeding. By evaluating how genotypes behave in different environments, we’re equipping breeders and policymakers with the tools to deploy varieties where they’ll thrive.”

Key Findings: Resistance, Stability, and Adaptation

Among the most rust-resistant varieties identified were EC16 (commercially known as Mundo Maya), Ruiru 11, Parainema, Catigua MG2, and IPR107. While EC16 recorded the lowest average rust score across all sites, its performance was inconsistent in certain regions. Parainema and Kartika 1, however, combined high resistance with strong stability, making them versatile candidates for widespread cultivation.

The study highlighted that pure Arabica varieties tended to show higher susceptibility to rust, whereas interspecific hybrids—particularly those with Timor hybrid parentage—offered stronger resistance. However, no variety demonstrated absolute immunity, underscoring the need for continuous surveillance and breeding innovation.

The Environmental Variable: No One-Size-Fits-All

Resistance was also found to be deeply influenced by site-specific environmental factors. Climate, altitude, rust strain diversity, and even agricultural practices contributed to varietal performance. Using advanced statistical tools like the GGE biplot and the WAASB model, the researchers identified four macro-environments or “mega-zones” that captured the variation across regions. Each zone had its own top-performing varieties and unique challenges.

For instance, Catigua MG2 thrived in India, Indonesia, and El Salvador, while EC16 and Ruiru 11 dominated in East Africa and parts of Central and South America. This knowledge enables breeders to tailor varietal recommendations more precisely, improving outcomes for smallholder farmers.

Albertino Meza, Agricultural Research Manager at CENFROCAFE, Peru, one of the trial’s host sites, remarked: “We now have evidence that empowers farmers. They can select varieties based on actual field data, not assumptions. This improves yield, resilience, and ultimately, livelihoods.”

Practical Implications for the Global Coffee Sector

The IMLVT trial provides direct benefits to multiple stakeholders in the coffee value chain:

• Breeders gain clear data on which parent lines offer reliable resistance.
• Producers get tools to select the right variety for their environment.
• Governments and NGOs can shape agricultural policies and training programs based on proven outcomes.
• Exporters and roasters gain a more stable supply of high-quality beans.

As the effects of climate change continue to amplify disease risks in agricultural systems, the value of such international research grows. With global coffee production facing volatility from both biological and environmental stressors, strategies rooted in collaboration, science, and adaptability are no longer optional—they are essential.

Building Scientific Infrastructure and Capacity

The trial didn’t only generate scientific knowledge; it also enhanced infrastructure and human capacity in the host countries. Partner institutions received equipment, training, and support to continue advanced agronomic research, building local resilience beyond the lifespan of the project.

“We’re building more than disease resistance—we’re building networks of trust and capability,” Dr. Humphrey said. “This trial sets a precedent for how global agriculture can respond to shared threats.”

Looking Ahead: Toward Next-Generation Coffee

With rust resistance proving variable across locations, the study underscores the need for ongoing multilocation trials, deeper genetic mapping, and surveillance for rust race evolution. It also opens pathways for stacking resistance genes, as previously proposed by Eskes and others, to provide more durable protection.

The study’s GxE framework also provides a template for evaluating other key traits, such as drought tolerance, cup quality, and yield potential. The future of coffee breeding is not just about one trait or one country—it’s about designing resilient, high-performing varieties for a complex and changing world.

The data is publicly available, serving as a resource for breeders, producers, and researchers. It also serves as a call to action: the future of coffee depends not only on preserving quality but on building systemic resilience. With shared science and shared purpose, the coffee community can rise to meet that challenge.

Download the full study: Global Coffea arabica variety trials reveal genotype-by-environment interactions in resistance to coffee leaf rust (Hemileia vastatrix) published in Frontiers in Plant Science.