The rust coffee is a fungal disease caused by Hemileia vastatrix, a basidiomycete belonging to the class pucciniomycetes. This fungus is an obligate parasite unable to survive in inert matter. Its first registration was made in Sri Lanka and is currently widely distributed worldwide.
The first symptoms of the disease are small, round, translucent lesions or spots that resemble drops of oil and appear on the leaves. At the time of their appearance, these spots do not exceed 3 millimeters in diameter. In its final stages, it causes premature leaf fall, branch death, and even the plant itself.
Uredinium of Hemileia vastatrix. Taken and edited from: Carvalho et al..
To control the disease, resistant plants can be used, planting management (densities, pruning, adequate fertilization, among others) and through the application of agrochemicals.
History
Coffee rust is one of the most catastrophic plant diseases in history, leaving heavy economic losses that place it among the seven plant pests that have caused the greatest losses in the last century.
The first documented record of an epidemic of Hemileia vastatrix attacking coffee crops dates from 1869 on the island of Ceylon, now known as Sri Lanka. On that occasion, the effects of the fungus were so devastating that the coffee growers, not knowing the causes of the disease and how to combat it, decided to eradicate the coffee trees and grow tea.
The pathogen spread rapidly and that same year it also struck in India. Within a decade after the first record of rust, it had already made an appearance in Sumatra, Java, South Africa and the Fiji islands.
In South America it was detected for the first time in 1970 in the state of Bahia, Brazil. Then it made its appearance in Nicaragua (1976), while in the 80's it is reported in Costa Rica and Colombia. It is currently present in practically all countries that grow coffee worldwide.
Symptoms
The first signs of infection of the plant are chlorotic lesions, with the appearance on the leaves of small pale yellow spots, similar to drops of oil that make the leaf translucent against the light.
These lesions, which do not exceed 3 mm in diameter, appear mainly towards the margins of the leaf, which are the regions where water tends to accumulate the most.
When sporulation begins, the lesions increase in size, up to 2 cm in diameter, and a yellow or orange powder appears on the underside of the leaf, which is formed by urediniospores. If there are many lesions of this type, the spots will join as they grow, occupying the entire leaf, which tends to detach.
When the rust spot goes into senescence, the urediniospore dust becomes paler. Then the yellow spot is being replaced from the center towards the periphery by a darker spot (brown or black) with a necrotic appearance and in which no spores will be produced.
In its most advanced stage, the disease causes the premature loss of the leaves and can cause the death of branches or even the entire plant by affecting the processes of photosynthesis, respiration and transpiration that take place in the leaves.
Detail of the suprastomatal uredinial pustules of Hemileia vastatrix. Taken and edited from: Carvalho et al..
Taxonomy
Hemileia vastatrix attacking a leaf of the coffee plant. Taken and edited from: Carvalho et al..
Crop management
The management of some variables of the coffee tree crop can help prevent, control or facilitate the eradication of the disease. Among these variables are planting density (2 meters between rows and 1 between plants), pruning (low post-harvest pruning), selection of healthy shoots, use of shade, and adequate fertilization.
Chemical control
Chemical control is one of the main components in a coffee rust control program. However, this represents a high economic and environmental cost. The success of its use will depend, among other factors, on the selection of the appropriate fungicide and its correct and timely application.
The alternate use of copper-based fungicides with other systemic fungicides is recommended to avoid the appearance of resistance to them. Currently there is abundant information on the efficiency of the different active ingredients as well as the appropriate doses of them.
Fungicides are also being developed that inhibit ergosterol synthesis in the fungus, such as difenoconazole and hexaconazole, or also a mixture of a strobilurin with a triazole.
References
- P- Talhinhas, D. Batista, I. Diniz, A. Vieira, DN Silva, A. Loureiro, S. Tavares, AP Pereira, HG Azinheira, L. Guerra-Guimarães, V. Varzea & M. Silva (2017). The coffee leaf rust pathogen Hemileia vastatrix: one and a half centuries around the tropics. Molecular Plant Pathology.
- HF Shiomi, HSA Silva, IS de Melo, FV Nunes, W. Bettiol (2006). Bioprospecting endophytic bacteria for biological control of coffee leaf rust. Scientia Agricola (Piracicaba, Brazil).
- Hemileia vastatrix & Broome 1869. In Encyclopedy of Life. Recovered from eol.org
- Biological control of coffee leaf rust. In World Coffee Research. Recovered from worldcoffeeresearch.org.
- Coffee rust. Recovered from croplifela.org
- J. Avelino, L. Willocquet & S. Savary (2004). Effects of crop management patterns on coffee rust epidemics. Plant Pathology.