Coffee rust is caused by the fungus Hemileia Vastatrix; Rust has a unique sounding name but is the most potent natural enemy of coffee plants. Rust remains a terrible disease, extremely unpredictable, and challenging to control for more than a century and a half after the first observation.
The truth is that without a complete understanding of the ecology of this fungus, it is impossible to understand exactly what can affect its growth and proliferation, let alone how to eradicate it – in the words of Emma Sage from SCA. This appears to be an example of how coffee scientific study lags behind other crops.
Rust and Coffee Rust?
First, we must understand that Coffee Rust, also known as Coffee Leaf Rust (CLR), is a fungus that causes plant rust. Rust is a group of fungi with biodiversity in the microbiological system. It has been extensively researched and impacts a wide range of plants. According to Wikipedia, there are 168 genera of Rust, with approximately 7,000 species. Each of these parasites can only live on one species of host. For example, the fungus Puccinia kuehnii causes sugarcane rust, P. sorb causes maize disease, and H. vastatrix exclusively causes coffee disease.
Ecology of H. vastatrix
The H. vastatrix has a complicated life cycle that begins with fungi capable of asexual reproduction and creating hundreds of microscopic spores. Because fungal spores are so light and tiny, they can travel on their own in water, rain, or air and live far from their original location. When a spore lands on a leaf, it can germinate and enter the leaf through the stomata when the conditions are appropriate (the opening on the underside of the coffee leaf, like a pore. feathers are used for air exchange).
The word “spore” is derived from the Ancient Greek [o spora], which means “seed or sowing.” 4 to 6 H. vastatrix spores per initial coffee leaf create 300 to 400,000 individual spores after 3-5 months, ready for a continuous cycle – Wikipedia
The fungus spores will proliferate and produce rust-like circular yellow or orange spots (colonies) on the undersides of leaves when the conditions are right, even though coffee is always mentioned as a necessary host to complete the H. vastatrix life cycle. Most scientists assume it had or still has an undisclosed other host in the past.
Research on coffee rust disease
Rust is now found almost anywhere coffee is cultivated, even though it only thrives in a specific climate and environment. The primary (and most essential) factor impacting H. vastatrix growth is free moisture (rain or heavy dew). Because water is required to germinate and spread fungal spores, disease outbreaks are most common during the rainy season.
Second, the temperature has an impact on rust formation. The spores will not germinate if the temperature is below 15°C, and the fungus will grow slowly if the temperature is above 35°C. The best temperature for rust growth and proliferation is between 21 and 25 degrees Celsius (Nutman et al. 1963).
On the other hand, light can alter how fungus damage coffee plants; however, there is some evidence to support this. The undersides of leaves that are not exposed to direct sunlight (high-intensity light) are more prone to Rust, and light can affect the rate of Rust on infected leaves. proliferation of fungus
Rust is induced by shade trees, excessive humidity, climate change, and other factors. Monoculture, in reality, is the true fury. Whenever man intervenes to promote the strong growth of a plant’s natural fruit, nature finds a new way to exploit that plentiful food supply.
Mark Pendergrast, Uncommon Grounds
Damage to coffee
The fungus causes a minor discoloration on the underside of the leaves when it first colonizes the coffee plant. These blobs turn yellow quickly, then a layer of orange “dust” — mature spores – forms on top. The photosynthetic power and metabolism of the leaves decline as the rust spots get more extensive and take up more of the leaf area, causing the leaves to fall prematurely. The fungus can emerge on young shoots or fruits in extreme cases. Researchers have discovered that older leaves are more resistant to fungal diseases and that H. vastatrix does not kill the plant completely.
When H. vastatrix attacks a coffee tree, it can lose a lot of leaves. It also loses its ability to run the metabolic cycle through photosynthesis and accumulate nutrients (or adequate resources) for fruiting when it loses its ideal leaf area. Even a few years after the rust pandemic has spread, coffee crops would fail yield.
There are scant quantitative records of productivity losses due to the difficulty of adequately accounting for CLR losses. Yield loss estimates vary by country and range from 15 to 80 percent. Early data from Ceylon (where the disease was initially discovered) reveals that coffee production has dropped by 75%. (Wikipedia)
But where does Rust come from?
Rust may have first emerged on wild Arabica coffee trees in Africa, although it was not “discovered” until the 1870s. The earliest documented pandemic impact happened in Ceylon (now Sri Lanka) in the early 1850s (according to Wikipedia, 1869 – in the Gardeners Chronicle), when a large epidemic decimated Arabica coffee and forced the island’s coffee industry to be replaced by tea trees.
Rust has spread from Ceylon to almost every coffee-growing country on the planet, with the first outbreak occurring between 1870 and 1920 in the Indian and Pacific coffee regions. Rust may have followed the winds, crossed the Atlantic to Latin America, and attacked the second and third times the illness was present in African countries in the 1950s and 1960s and the last time. In the 1970s and 1980s, Bahia state, Brazil. Despite the most significant efforts to suppress the disease, it spread over Central and South America roughly 15 years after it originated in Brazil.
Due to the convergence of various agronomic, meteorological, and economic conditions (season 2012 – 2015), CLR has lately regained popularity amid a severe and widespread outbreak over Central America, Colombia, Peru, and Ecuador. Up to 35% of productivity is lost, hurting the earnings and livelihoods of hundreds of thousands of farmers and employees.
Historians believe that the loss of coffee production in Sri Lanka was one of the reasons why the British preferred tea, as Sri Lanka was once the colony that supplied the majority of the coffee to the British in the nineteenth century.
The fight against rust disease
H. vastatrix control is a challenging undertaking; there is no easy fix for this problem. Outbreaks have occurred, revealing H. vastatrix’s ability to grow over a long period. Fungicides have been used to control outbreaks of coffee rust since they expanded over the world’s producing regions. Propiconazole, Trasimeno, tridemfon, and copper oxychloride are only partially efficient fungicides. Copper-based fungicides are the most popular, but they have a short period of activity and must account for the impacts of H resistance. vastatrix.
Copper-based fungicides can be helpful as a preventive treatment. Still, they should be used in conjunction with a total fungicide (such as epoxiconazole or pyraclostrobin) in the case of an outbreak to avoid the danger of fungal resistance.
Because of health and environmental concerns, less reliance on fungicides has forced increasing research to produce better, more effective, long-lasting disease control alternatives. One example is using bacteria and fungi in the coffee ecosystem as a potential biocide against H. vastatrix. Bacterial strains like Pseudomonas putida, Bacillus megaterium, and Bacillus thuringiensis have been identified and have demonstrated promising anti-CLR activity. However, more research into this idea is required.
Disease resistant breeding
The best disease management technique, both environmentally and economically, is to propagate coffee plants for rust resistance. With the introduction of the Kent variety in India in 1911, the first successful attempt to select genetic resources for disease resistance was made. However, after around ten years of culture and exposure to the pathogen, this resistance was gone. In C. Liberica and C. Canephora, this gradual resistance decrease was also seen. This has led to the identification of more “species” of coffee rust than previously thought – more than 45 have been identified to date (Muller et al., 2009).
The Rusts strain has the largest average genome size among fungi, and the genome of H. vastatrix ranks first among the Rusts with about 797 Mbp (Ramos et al., 2015; Tavares et al. ., 2014) – This shows how little we know about the CLR.
CIFC and Hibrido de Timor hybrid
Back in the 1950s, when rust concerns reached the South American continent. This led the United States and Portugal governments to provide financial support for the establishment of the Coffee Research Center (CIFC). CIFC’s mission in Portugal is to focus research on Rust at an international level. Since 1955, CIFC has received and characterized coffee rust and provides breeding programs and scientific and technical training. One of the first practical results of the CIFC was the demonstration that all cultivars grown at that time in Latin America (including Typica, Caturra, Mundo Novo, and Bourbon ) were susceptible to CLR.
With the discovery of the Hibrido de Timor (or Timor Hybrid) population on the island of Timor in 1927, the first rust-resistant genes were introduced in the 1950s. Timor trees are natural hybrids between Arabica and Robusta, with resistance to all known rust strains at the time. In 1960, CIFC began a breeding program to transfer resistance from Timor to other Arabica varieties; Caturra and Villa Sarchi were crossed at CIFC to have produced populations of Catimor and Sarchimor, respectively. These populations were developed in Colombia and Brazil and became the primary source of later CLR-resistant varieties.
Finally, some knowledge has been accumulated about Rust and modeling in scientific reasoning. Yet disease management strategies have often proved ineffective. This gap can be objectively explained by the many environmental changes facing the coffee industry. But, fluctuations in the price of the coffee economy are also responsible for production. When prices do not guarantee livelihoods, farmers are forced to choose between organic farming, risk disease, or using fungicides as an economically safe remedy.