Hemileia vastatrix

Hemileia vastatrix is a multicellular basidiomycete fungus of the order Pucciniales (previously also known as Uredinales) that causes coffee leaf rust (CLR), a disease affecting the coffee plant. Coffee serves as the obligate host of coffee rust, that is, the rust must have access to and come into physical contact with coffee (Coffea sp.) in order to survive.

CLR is one of the most economically important diseases of coffee, worldwide. Previous epidemics have destroyed coffee production of entire countries. In more recent history, an epidemic in Central America in 2012 reduced the region's coffee output by 16%.

The primary pathological mechanism of the fungus is a reduction in the plant's ability to derive energy through photosynthesis by covering the leaves with fungus spores and/or causing leaves to drop from the plant. The reduction in photosynthetic ability (plant's metabolism) results in a reduction in quantity and quality of flower and fruit production, which ultimately reduces the beverage quality.