No single arabica coffee variety is entirely immune to coffee leaf rust (CLR) across different growing regions, a new global study led by researchers from 15 countries has found. The experts emphasize continuous monitoring and adaptation to develop resistance to evolving disease pressures. 

The data released by World Coffee Research (WCR) shows that the 29 Coffea arabica analyzed varied significantly by location, with some varieties performing well in specific environments and poorly in others.

“No single country or institution can solve the complex challenges facing coffee on its own,” says Dr. Tania Humphrey, the scientific director of WCR.

“This trial shows the power of global collaboration — by pooling data, expertise, and resources across continents, we can 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.”

The findings come from the International Multilocation Variety Trial, which assessed the arabica varieties under natural CLR infection across 23 field sites globally during the 2020–2021 harvest season. The regions ranged from hot and dry places like Zambia to wetter geographies like Gambung, Indonesia.

According to WCR, this is the most extensive evaluation of arabica coffee varieties under diverse environmental conditions yet. The study is published in the scientific journal, Frontiers in Plant Science.

Coffee under threat

CLR, caused by the fungus Hemileia vastatrix, remains a major concern for the coffee sector.

The disease has over 55 identified races to date and can result in defoliation, poorer bean quality, and yield losses ranging from 35% to over 75% in severe cases.

CLR was first identified in the 19th century but has since reappeared in almost all coffee-growing regions, with Hawaii being the latest hotspot in 2020.

“Identifying host resistance for managing diseases like CLR is crucial in enhancing the profitability and sustainability of Kenya’s coffee sector while promoting environmental health,” says Dr. Elijah Gichuru, the institute director of Coffee Research Institute, Kenya Agricultural and Livestock Research Organization.

“Participating in this global research activity strengthens our efforts to combat coffee rust and reminds us that we’re not alone and that scientists worldwide are working together to solve shared challenges for the benefit of stakeholders.”

Best bets amid complexity

Farmers typically use coffee varieties resistant to rust to minimize economic losses from the disease.

However, WCR notes that resistance depends on the genetic makeup of the coffee plant and the pathogen. Commercial arabica varieties often carry combinations of resistant genes, but no single variety contains all the known resistance genes.

Additionally, the pathogen’s continuous evolution requires ongoing efforts to identify and incorporate new sources of resistance.

The study found that some varieties, like Parainema, Kartila 1, and IPR107, showed a promising combination of strong resistance to CLR and stable performance across environments, making them good overall choices for rust resistance.

Others, like EC16 and Catigua MG2, demonstrated very high resistance in some locations but weren’t as strong in others, with performance not being as “stable” across sites. These varieties perform best under certain conditions.

Pure arabica varieties typically showed higher susceptibility, wheras those with interspecific introgressions, such as Timor hybrid derivatives, reflected greater resistance.

“Our results allow breeding programs to narrow down on useful variation and inform breeding strategies,” says Dr. Jorge C. Berny Mier y Teran, WCR research scientist for Plant Breeding & Genomics.

The researchers call for deeper research into the genetic foundation of the resistance and its interaction with the environment.

Beyond scientific insight, the trial provided national research programs with new tools, training, and infrastructure, improving local capabilities while linking scientists across continents. Many participating regions now have more resources to track disease threats, conduct field trials, and adapt to climate change.

“Understanding rust can be complex for farmers. By identifying which varieties 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, a Peruvian cooperative with 2,400 members.