New species of bacteria is affecting walnut quality and production in Portugal

Researchers from the Faculty of Sciences of the University of Porto (FCUP) have discovered a new species of pathogenic bacteria in the walnut tree that affects the quality of the nut and threatens its production in Portugal.

The study, carried out with the Center for Research in Biodiversity and Genetic Resources (CIBIO-InBIO), focused on the main species of bacteria (Xanthomonas arboricola pv. Juglandis) that causes disease in walnut, namely walnut bacteriosis.

The characteristic symptoms of walnut bacteriosis include necrotic stains on the leaves and fruits, the early fall of the nut or the death of the embryo inside the fruit, causing considerable losses of production, decreased quality of the nut and considerable economic losses.

Following this study, published in the International Journal of Systematic and Evolutionary Microbiology, the researchers discovered a new species of pathogenic bacteria, which they called Xanthomonas euroxanthea. The two strains, although very similar, differ in their ability to infect walnut, which could be useful to identify new genes involved in this pathology.

Leonor Martins, the first author of the article, explains that this is the “first time that pathogenic and non-pathogenic strains of the same species of Xanthomonas have been observed to colonize the same plant (...) These results are quite promising, as the scientific community now has a favorable model for studying the emergence and evolution of pathogenicity, as well as the coevolution of batteries that have a walnut habitat".

In parallel, the researchers characterized the epidemic behavior of the isolated Xanthomonas population, based on plant material from walnut trees grown in different regions of the country.

According to Fernando Tavares, CIBIO-InBIO researcher and FCUP professor who led the group, the researchers' next objective is to study the genes essential to the virulence and pathogenicity of the new species of bacteria that can be used as markers for the detection of pathogenic strains or particularly virulent.

The research, carried out as part of the EVOXANT project, financed by European and national funds, resulted from a collaboration with the Zurich University of Applied Sciences in Switzerland.