Genome of the fungus that weakens olive groves deciphered for the first time: a new discovery from Córdoba opens the way to more resistant varieties
Olive growing, one of the most important agricultural branches in the Mediterranean area, has in recent years been facing a series of pressures, from climate extremes and changing market conditions to increasing exposure to plant diseases. Among them, olive cercosporiosis is being highlighted more and more often, a leaf disease caused by the fungus
Pseudocercospora cladosporioides. It is a pathogen that attacks the olive tree and wild olive, causes leaf loss, weakens vegetative growth, and can reduce yield and crop quality. That is precisely why the new research by the University of Córdoba represents an important step forward: scientists have for the first time managed to sequence and publicly publish the complete genome of this fungus, thereby opening the way for more precise disease monitoring and the development of more resistant varieties.
The new sequencing is not merely a technical success of laboratory genetics. In practice, it means that researchers now have at their disposal a kind of “instruction manual” for the pathogen, that is, a complete genetic map showing how the fungus functions, how it attacks the host, and by which mechanisms it adapts to the environment. For agriculture that in countries such as Spain has a strong economic, landscape, and social role, such knowledge can have very concrete consequences: from earlier recognition of risky strains to smarter breeding of plantations and more rational plant protection.
A disease that for a long time was not at the center of attention
Olive leaf cercosporiosis is described in the scientific literature as one of the most important foliar diseases of olive in the world, especially in the Mediterranean area. Symptoms are most often seen on the leaves. On the upper side, light green to yellowish spots appear that over time can become necrotic, while on the underside characteristic lead-gray areas develop associated with the fungus’s fruiting bodies. The consequence is not only aesthetic damage to the canopy. Infected trees may shed leaves earlier, have weaker shoot growth, poorer formation of fruit buds, and delayed fruit ripening, and in stronger infections the disease can also affect the quality and quantity of production.
Scientific papers by the University of Córdoba published in previous years showed that this is a disease that in many olive-growing areas had long been underestimated. Partly because in practice it was often observed alongside other olive diseases, and partly because the biology of the pathogen itself was difficult to study. Researchers state that the fungus grows slowly outside the host, is demanding to cultivate under laboratory conditions, and that precisely for this reason it was very difficult to obtain genetic material of sufficient quality for serious genomic analysis. This technical problem had for years represented the main obstacle.
An additional reason for the growing interest in cercosporiosis lies in changes in production itself. In Spain, according to the researchers, more sensitive varieties had been spreading, among them the Italian cultivar Frantoio, while at the same time in plant protection there is an increasingly pronounced trend toward reducing the use of copper-based preparations. Such circumstances do not mean that one measure in itself is the cause of the problem, but they create a more favorable framework for the spread of a disease that develops better when preventive protection weakens and more sensitive genotypes prevail in plantations.
Why the genome matters for fruit growers and breeders
When it is said that the fungus genome has been sequenced, in translation this means that scientists have succeeded in reading the pathogen’s complete hereditary record. It is precisely in that record that the instructions are found for building cellular structures, producing proteins, spreading infection, and overcoming the plant’s defense responses. Without such a map, research into the relationship between the pathogen and the olive remains incomplete, and the development of more resistant varieties relies more on prolonged trial and error than on targeted searching for useful traits.
In the new paper, published in 2026 in the journal
Plant Pathology, the research team states that a genome of 53 megabases was assembled and that more than 14,000 genes were identified. This result was achieved by combining short- and long-read DNA technologies, which today is standard when a higher-quality and more stable genomic assembly is sought. But the size of the genome itself is not the most important part of the story. The key lies in what followed after sequencing, namely genome annotation, that is, the recognition and functional interpretation of individual genes.
It was precisely that phase that enabled a deeper insight into the fungus’s attack strategy. According to the data from the paper, the researchers identified 491 genes associated with the degradation of the olive cell wall. This is an exceptionally important finding because the cell wall represents one of the plant’s fundamental defensive barriers. If the pathogen has at its disposal a broad set of tools for its destruction, then it is clearer why the infection can be so persistent and why the disease leads to weakening of the leaf and premature shedding. In addition, 434 effector proteins were also identified, molecules that, simply put, help the fungus silence or bypass the host’s defense mechanisms.
Such data are important far beyond one laboratory. For breeding programs, they mean that olive resistance can henceforth be sought more precisely, with a focus on genes and biological processes that are now known to be key in the conflict between plant and pathogen. In other words, it is no longer just a matter of observing that a variety is “more resistant” or “more susceptible,” but of trying to understand why that is so and whether that response can be transferred into new selections.
The biggest obstacle was obtaining high-quality DNA and RNA material
Although the final result sounds like a natural continuation of the development of genomics, in this case the path to the goal was anything but simple. The team itself states that the key challenge consisted in obtaining high-quality DNA and RNA. For many plant pathogens this is a demanding but routinely feasible procedure. In the case of
Pseudocercospora cladosporioides, the situation was considerably more complex because the fungus is not easy to isolate outside the host and maintain under conditions that allow a sufficiently pure and stable sample.
That is why the development of a precise isolation protocol was important. Only when quality biological material had been secured was it possible to move on to sequencing and bioinformatic processing. In that sense, the study brings not only the final result, but also methodological progress that will benefit other research groups as well. In science, this is often just as important as the headline finding itself: once a reliable method has been established, room opens up for other laboratories to apply it, verify it, upgrade it, and use it in new comparative analyses.
This is especially important in diseases such as olive cercosporiosis, which do not always attract the same attention as some more spectacular epidemics in agriculture, but in the long term can have a major effect on the economics of production. The disease develops slowly, the symptoms are sometimes confused with other problems in the plantation, and part of the damage becomes visible only through reduced tree vigor and a weaker harvest in the following seasons. That is precisely why a thorough understanding of the pathogen can be more important than short-term improvisations in protection.
The Spanish context: olive is a strategic crop, and diseases have a wide impact
The importance of research like this grows even further when the weight of olive growing in Spain and in the Mediterranean is considered. Earlier expert papers remind us that Spain had for years been the world’s greatest power in olive oil production, with enormous areas under olive trees, while Andalusia is the center of that production. The International Olive Council in its latest statistics from March 2026 also confirms Spain’s key role in the global olive oil and table olive sector. When a disease affects such a production system, the consequences are not measured only in agronomic terms, but also through producers’ income, supply stability, investments in protection, and pressure on research institutions to find more sustainable solutions.
In that context, the estimate that cercosporiosis can cause large annual losses is understandable. An amount of up to 50 million euros per year appears in materials accompanying this topic and speaks primarily about the economic seriousness of the problem, although the level of damage by definition depends on the year, the intensity of infection, the assortment of varieties, the climatic conditions, and the cultivation model. In any case, this is a disease whose burden is not exhausted in one treatment or one growing season, but spills over into production planning, variety choice, and protection costs.
In addition, it should be borne in mind that European agriculture in recent years has been moving toward reducing the use of certain plant protection products, stricter residue monitoring, and broader introduction of integrated approaches. This is an important and expected direction in the long term, but at the same time it demands more precise knowledge from growers and science about the pathogens themselves. In other words, the narrower or more targeted the possibilities of routine chemical protection become, the greater the need for early detection, genetic resistance, and a better understanding of disease biology.
The synergy of agronomists and geneticists as a model for complex agricultural problems
One of the most striking messages of this research is that the result was not achieved through the work of one narrowly specialized group, but through the cooperation of multiple disciplines. The University of Córdoba emphasizes that the departments of agronomy and genetics played a key role in the project. Phytopathologists had knowledge of the disease, fungal isolation, and work with plant pathogens, while the genetic part of the team brought expertise in sequencing, annotation, and bioinformatic processing of enormous amounts of data. Only the combination of those competencies made it possible to turn a technical problem into a scientific breakthrough.
Such a working model is becoming increasingly important in modern agricultural science. Diseases of woody crops, especially long-lived ones such as olive, cannot be effectively studied only at the level of field symptoms nor only at the level of computer analysis in the laboratory. Field experience, classical phytopathology, molecular biology, and bioinformatics are all needed. In that sense, this paper goes beyond the topic of one fungus: it shows how complex food production problems are solved today.
The research was created within the broader framework of the European Gen4Olive project, coordinated by the University of Córdoba. The project, funded by the Horizon 2020 program, brings together 16 partners and is aimed at bringing olive genetic resources closer to breeders and producers. That framework is not an unimportant detail, but rather shows how European research policy is increasingly oriented toward connecting basic science with the concrete needs of agriculture. When the genome of one fungus becomes publicly available, not only the laboratory that published it benefits, but also the wider research community, which can compare populations, track the evolution of the pathogen, and develop tools for monitoring.
What the new knowledge can change in practice
An openly available reference genome is also important for future disease monitoring systems. Once the complete genetic structure of the pathogen is known, it becomes easier to develop molecular tests for its faster and more sensitive detection. This can be especially useful in situations when symptoms have not yet fully developed or when they are difficult to distinguish from other problems on the leaf and fruit. For producers and advisory services, this means the possibility of reacting to the presence of the pathogen earlier and more precisely, rather than only when the damage becomes visually obvious.
The second area of application is monitoring the evolution of the fungus. Pathogens are not static organisms. Populations change over time, adapting to climatic conditions, host assortments, and the pressures created by plant protection. Without a reference genome, such changes are much more difficult to track. With the genome in hand, researchers can compare isolates from different regions, look for differences associated with aggressiveness or possible adaptation, and detect earlier trends that could become a problem for production.
Third, and perhaps most important in the long term, is breeding. The development of resistant olive varieties is a slow process, because it is a perennial crop in which every selection step requires time. But more precise knowledge of infection mechanisms can make that process more efficient. If it is known which plant defense barriers the fungus most often attacks and which proteins it uses to suppress resistance, then it becomes easier to define breeding targets and molecular markers that could help in selecting promising genotypes.
Research without sensationalism, but with clear value
At a time when scientific news is often simplified to the level of spectacle, this discovery is more important precisely because it does not promise a miraculous solution overnight. Genome sequencing will not by itself stop cercosporiosis in olive groves, nor will it produce a new universally resistant variety as early as next season. It does, however, create a tool without which serious progress is not possible. In that sense, this is infrastructural knowledge: perhaps less visible to the wider public, but crucial for everything that follows.
For olive producers and the regions that build a large part of their economy on this crop, this is important news because it shows that production protection is relying less and less exclusively on experience-based measures, and more and more on a deep understanding of pathogen biology. For the scientific community, this is a reference point that will serve as a basis for future research into the interaction between olive and fungus. And for European agriculture as a whole, this is an example of how multidisciplinary cooperation can deliver a result with very concrete potential, from early disease detection to olive groves that are more resistant in the long term.
Sources:- Wiley / Plant Pathology – scientific paper on the first high-quality genome of the fungus Pseudocercospora cladosporioides- MDPI / Agronomy – overview of symptoms, disease biology, and control strategies for olive cercosporiosis Evaluation of Fungicides and Management Strategies against Cercospora Leaf Spot of Olive- University of Córdoba CRIS – data on earlier work on the susceptibility of new olive varieties to Pseudocercospora cladosporioides- GEN4OLIVE – official data on the European project linking olive genetic resources, breeding, and research teams Gen4Olive- International Olive Council – latest overview of the situation and statistics of the olive oil sector from March 2026 Olive sector statistics – February/March 2026
Find accommodation nearby
Creation time: 5 hours ago