Kiel Plant Center

Wagner Fagundes - fungal pathogens in wheat

Wagner Fagundes is a PhD student in Eva Stukenbrock’s group in the botanical institute at the University of Kiel. He is interested in understanding the relationship between fungal pathogens and their hosts, and how new pathogens evolve. Here he explains more about his research into the evolutionary history of Zymoseptoria tritici, a widespread fungal pathogen in wheat.

Scientist in the lab
Wagner Fagundes in the lab at Kiel University. Copyright: KPC / Rosemary Wilson

 

What is Zymoseptoria tritici?

Zymoseptoria tritici is a fungal pathogen that causes a lethal disease known as Septoria tritici blotch in wheat plants. It is actually a really serious problem in crop production. Zymoseptoria tritici is found in wheat wherever the crop is grown around the globe. Particularly here in Europe it is one of the most destructive wheat diseases. Wheat is so central and essential to our society, that economically, and in terms of food security, Zymoseptoria tritici is a real problem. Now that the fungus is also developing resistance to many widely used fungicides, it is becoming even more of a problem, and we will need to find new ways to protect the health and yield of the crops.

 

How does the fungus infect the plants?

The spores land on the leaves and enter the leaf via the stomata. They need high humidity to germinate and to ensure that the stomata are open so they can enter the plant. Zymoseptoria tritici has two distinct infection phases, referred to as a biotrophic and a necrotrophic phase. In the biotrophic phase the plant shows no obvious symptoms that the plant is infected, even though the fungus is present and has already colonized the substomatal area and the surrounding tissue. Then about two weeks after infection, irregular brown patches called lesions appear on the leaves, marking the necrotrophic phase and subsequent wheat cell death. Around three weeks after infection, fruiting bodies known as pycnidia appear on the necrotic leaves. These small structures look like a black mass and bear several fungal spores ready for dispersal via rain splashes.

Wheat leaf with visible fungal infection
Wheat leaf displaying brown lesions caused by the fungus Zymoseptoria tritici. Copyright: Janine Haueisen
 

How long ago did Zymoseptoria tritici first emerge as a pathogen in wheat?

Studies seem to suggest the pathogen has been associated with wheat since humans first domesticated it around 11,000 years ago. It seems the pathogen emerged from related species of wild grass at the same time and has followed a similar evolutionary history to its host. So, it seems both organisms have had a very close relationship since wheat domestication.

 

What is the focus of your research?

A few years ago our group received samples of wild grasses from the Middle East that seemed to be infected by Zymoseptoria tritici. This was really curious because it is known that Zymoseptoria tritici is specialized to infect wheat. Now we were seeing what seemed to be this same fungus on wild grass species. This was really unexpected, but interesting also given the fact that the Middle East was the center of origin of Z. tritici. My colleagues isolated the fungal spores from the plant to check more closely, and indeed it seems to be Zymoseptoria tritici. This raised so many questions. Is it perhaps the original ancestral species – it came across from a wild grass to wheat in the first place after all – or is it genetically an independent lineage? So maybe it looks similar but is genetically quite different to the wheat pathogen. Maybe it moved back to grass from the domesticated wheat, or maybe the fungus is not as specific as we thought. This also raises more general questions about how fungal pathogens emerge and their evolutionary relationship to their hosts. That is where I came in. The main focus of my PhD is to understand how fungal pathogens, in this case Zymoseptoria tritici, adapt to their hosts, and how new pathogenic fungal species or lineages develop.

 

How are you doing this exactly?

In the lab I have sequenced the genomes of about 116 isolates, that means the fungal samples isolated from the plants. This includes samples from both the wild grasses and wheat, and we have compared these with each other in order to determine the genetic difference between the individuals growing on the different plants. I should point out that we have been looking at Zymoseptoria samples taken from wheat grown in the same geographical region as the wild grass species. Here we may see whether the fungal populations really are genetically similar or distinct even if they occur in the same area.

We are also doing experiments in the greenhouse to test the host range of the fungus. Here we are inoculating a range of different wild grass species and wheat relatives with the Zymoseptoria tritici spores acquired from the grass species to see whether, and if so which, become infected.

Scientist in the greenhouse inspecting plants
Wagner checks whether wild grass species are susceptible to infection with Z.tritici in the greenhouse. Copyright: KPC/ Rosemary Wilson

What do you hope to be able to achieve with your research?
We can already see that these Zymoseptoria tritici genomes are really diverse. Because of this diversity, they may well have a great evolutionary potential. This means the ability to potentially adapt to new hosts, environments and maybe even climates. This might suggest that Z. tritici is actually adapted to a wider host range than we used to believe.

I would love to mine the data we have further to find determinates or genes which might indicate pathogenicity. This is part of what is known as functional genomics – looking at the genetic data to decide what connections there are between candidate genes and to know how they can impact the characteristics we are seeing in the organisms.

Ultimately it would be nice to be able to understand how the environment and our own actions benefit the emergence of new pathogens and develop recommendations that might counteract that. For example, maybe we find out that planting wheat next to related grass species benefits the emergence of new or related pathogen lineages or species, because we are making it easy for the pathogen to move from one plant to the other. So we could advise against this planting regime as a measure to better protect the health of the crops. It would be nice to show both a theoretical and an applied plant pathology application with my work. Let’s see how far we get!