Vítor Várzea, Sílvia Tavares, Pedro Talhinhas, Inês Diniz, Andreia Loureiro, Diogo N. Silva, Leonor Guerra-Guimarães, Ana Vieira, Maria do Céu Silva, Helena G. Azinheira, Ana Paula Pereira, Dora Batista
Taxonomy and History
Hemileia vastatrix Berk. and Broome (Basidiomycota, Pucciniales) was described in 1869 in eastern Africa and Ceylon as the agent of coffee leaf rust and has spread to all coffee cultivation areas worldwide. Major disease outbreaks in Asia, Africa and America caused and continue to cause severe yield losses, making this the most important disease of Arabica coffee, a cash crop for many tropical and sub-tropical countries.
Life cycle and Disease symptoms
Hemileia vastatrix is a hemicyclic fungus with the urediniosporic life cycle as its most important (if not only) source of inoculum. Chlorotic spots are the first macroscopic symptoms, preceding the differentiation of suprastomatal, bouquet-shaped, orange-coloured uredinia. The disease can cause yield losses of up to 35% and have a polyetic epidemiological impact on subsequent years.
Although the use of fungicides is one of the preferred immediate control measures, the use of resistant cultivars is considered to be the most effective and durable disease control strategy. The discovery of ‘Híbrido de Timor’ provided sources of resistance that have been used in several breeding programmes and that have been proven to be effective and durable, as some have been in use for more than 30 years.
Genetic diversity and Molecular pathogenicity
Although exhibiting limited genetic polymorphism, the very large genome of H. vastatrix (c. 797 Mbp) conceals great pathological diversity, with more than 50 physiological races. Gene expression studies have revealed a very precocious activation of signalling pathways and production of putative effectors, suggesting that the plant–fungus dialogue starts as early as at the germ tube stage, and have provided clues for the identification of avr genes.