CoffeeRES - Coffee leaf rust

Coffee leaf rust (CLR) caused by the biotrophic fungus Hemileia vastatrix is one of the main limiting factors for the sustainable farming of Arabica coffee, which currently represents 60% of the world’s coffee production. The disease causes losses of over $1 billion US dollars annually.

H. vastatrix is a hemicyclic fungus producing urediniospores, teliospores, and basidiospores. Urediniospores are dikaryotic and represent the asexual cycle, re-infecting the leaves whenever environmental conditions are favorable. H. vastatrix infects the lower surface of the leaves where it produces chlorotic spots preceding the differentiation of supra stomatal, bouquet-shaped, orange-colored uredinia, leading to premature defoliation.

CLR was first recorded in 1861 near Lake Victoria (East Africa), but it caused the first major outbreak in 1869 in Ceylon (now Sri Lanka), causing the eradication of coffee cultivation in this country.

The disease spread through coffee-growing countries of Asia and Africa until 1950. In the Americas, CLR was first detected in Brazil in 1970 and dispersed progressively across the coffee plantations of other Latin American countries. In Hawaii, CLR was reported for the first time in 2020. Nowadays, CLR is present in all coffee-growing regions.

In the last decade, the epidemic resurgence of CLR, known as "the big rust", had strong economic and social impacts on several countries across Latin America and the Caribbean. Moreover, CLR has been reported to have expanded its area of distribution to regions of higher altitude where previously was not detected, namely above 1000-1100 m in Central America and above 1600 m in Colombia. It has been associated with changes in climatic conditions, the ecology of coffee farms, and recurring economic shocks.

CLR Management

Chemical control (e.g., Copper-based and systemic fungicides) is expensive, represents an environmental hazard, and social concern (organic coffee is increasingly valued)
Cropping practices (e.g., pruning, fertilization, and shade management)
Plant resistance inducers (e.g., cell wall fragments, plant extracts, and synthetic chemicals) mimic a pathogen infection and thus, activate a sort of unspecific systemic immunity, known as systemic acquired resistance (SAR).
Biological control (e.g., Bacteria and fungi present in the coffee ecosystem)
Disease resistance breeding: the use of coffee-resistant varieties is the most sustainable, efficient, and eco-friendly strategy for disease control

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