(From left to right). Wladimiro Diaz, Luis F. Arias-Giraldo and Vicente Arnau.

Researchers from the universities of Valencia and Córdoba, as well as the Institute of Sustainable Agriculture of the CSIC have studied the verticillosis fungus, a disease that kills millions of olive trees. Through observation of the microbiome of olive roots, they conclude that verticillosis is driven by a large community of microorganisms that band together to attack plants, a fact that rethinks the way to deal with it. The results have been published in the prestigious journal BMC Plant Biology.

The work has its origin in the TFM of Luis F. Arias-Giraldo, titled in the Master of Bioinformatics of the Universitat de València, which was supervised by researchers from the Institute of Integrative Systems Biology (I2SysBio) Vicente Arnau and Wladimiro Díaz, and Carlos P. Garay from the CSIC.

Olive verticillosis is one of the most devastating pests for the olive grove and one of the main phytosanitary problems in the sector. The disease, also known as 'La Seca', is caused by a fungus - Verticillium dahliae - that remains in infected soil, colonizes the roots and plugs the vascular system until causing the death of the plant, which produces effects similar to those of a severe drought. As Vicente Arnau, professor in the area of ​​Computer Architecture and Technology, highlights, the infection is analyzed from the point of view of systems biology: "We do not focus on the interaction between two species, but we analyze how all the species present in the olive tree ecosystem interact.”

The study has shown that the infection, for which there is no effective cure, is much more complex than previously thought. The work has studied the dynamics of the microbiome of infected roots and concludes that the infection process involves many more contenders. Although the disease is initially directed by the fungus verticillium, it is not driven by a single species, but by an entire community of microorganisms that attack the tree.

As the researcher from the Department of Biochemistry and Molecular Biology of the University of Córdoba Antonio Rodríguez Franco points out, the results suggest that the wilting of the olive tree due to verticillosis “must be understood as a systems biological process in which an interaction takes place complex.”

According to the research itself, there are several fronts that take place in this kind of microscopic war declared by the verticillium, but to which other organisms are added. As Arnau explains, “during infection there is a biological succession of different types of parasites that could explain the parasitic alternations observed and described in many infectious systems.”

Various types of fungi, bacteria and protozoa act as a consortium to attack the tree. A series of opportunistic microbes also come into play, such as nematodes and amoebas, which, although they do not initially participate in the infection, feed on the substances generated by the olive tree's defenses to counteract the attack. Finally, the beneficial fungi that until now had maintained a symbiotic relationship with the roots of the tree, change their ally and become harmful to the plant itself.

This is, broadly speaking, the dynamics of a contest whose final result is the withering of thousands of olive trees in the Mediterranean basin and which has been detailed after analyzing RNA samples and carrying out a metatranscriptomic study of different samples.

The results, according to the article, could contribute to focusing future treatments to alleviate a disease that has increased in recent years due to the intensification of plantations in infected soils. For the moment, however, there are still several unknowns to be resolved, such as the genes involved in the plant's defense processes and revealing why some olive tree species are immune to infection.

Article:

Martí J.M., Arias-Giraldo L.F., Díaz-Villanueva W., Arnau V., Rodríguez-Franco A., Garay C.P. "Metatranscriptmic dynamics after Verticillium dahliae infection and root damage in Olea europaea." BMC Plant Biology volume 20, Article number: 79 (2020)