Supervising team: Marina Müller, Matthias Rillig, Jasmin Joshi
Workplace: ZALF Müncheberg
0. Brief expected profile of PhD student
Candidates must have a completed MSc in Microbiology, Phytomedicine, Microbial Ecology, Environmental Microbiology, Biotechnology or similar qualification. Previous experience in (1) culture-dependent and culture-independent methods for the detection and identification of microorganisms, (2) common microbiological, biochemical and ecological methods, (3) field and landscape studies, (4) ArcGIS and R statistics are desirable.
Ability to conduct field work independently, willingness to combine creative thinking with extensive laboratory work is an absolute prerequisite.
1. Short Abstract
Mycotoxin producing fungi of the genera Fusarium and Alternaria cause several economically relevant diseases of cereals and therefore, they are the focus of interest in this project. A complex set of abiotic and biotic factors mediates their dispersal via the crop canopy within a field as well as through the air from field to field. This dispersal depends on the specific traits that are typical for spores of Fusaria and Alternaria and their ability to disperse with the wind over different distances. Additionally, the spore formation on cereal leaves and ears as well as the assertiveness of the immigrating spores in a new habitat depends on the aggressiveness of the fungi and on the competition with the bacteria and fungi that are already present here. Here, we ask which of two characteristics is more important for a successful infection of wheat plants by phytopathogenic fungi: a high dispersal ability or a strong competitive ability? Experiments in a wind tunnel and in agricultural fields within the AgroScapeLabs will reveal the distribution of phytopathogenic fungi in space and time and how this is influenced by the interactions between bacteria and fungi in the phyllosphere of wheat plants in the habitats of origin and immigration.
2. Background and previous work (focus on PhD cohort 1)
Previous studies have identified the temporal and spatial distribution patterns of phytopathogenic Fusarium and Alternaria fungi as well as the distribution patterns of one of their most severe bacterial antagonist groups, the fluorescent pseudomonads. We analyzed changes in the abundance and community structure of these fungi as well as of the pseudomonads on the above-ground parts of wheat plants at three sampling dates in two growing seasons. We detected a strong correlation between climatic conditions and the abundance of the fungi, but depending on the fungal genera in a different way. Fusarium fungi only grew in places with increased humidity with marked temporal variations. The spore spread of this genus also varied in time and space. In contrast, Alternaria fungi were more homogeneously distributed within the wheat fields, their hot spots were rather in dry places with higher temperatures and lower moistures. Fluorescent pseudomonads were detected in high abundances in all sites of the wheat fields, but the proportion of antagonistically active pseudomonads fluctuated in space. Lab experiments showed that the antagonistic activity of these bacteria was more directed against Alternaria fungi than against Fusarium fungi. A direct relationship between the spore dispersal, the occurrence of fungi and bacteria and the antagonistic activities has not been found so far.
The aims of this project are:
- to select Fusarium and Alternaria strains with different spore types (ascospores, conidiospores) as well as Pseudomonas strains with different antagonistic activity
and their ability to spread over different distances (wind tunnel experiments, plot experiments)
- to assess the ability of these fungal strains to infect wheat plants with different indigenous bacterial and fungal populations (after artificial inoculation with differently active antagonists)
- to track specific strains from one plant to another (in the wind tunnel) and from one site to another (in a field plot experiment) by means of stable isotope tracking methods or by selection of antibiotic resistances
- to compare fungal communities in agricultural wheat fields surrounded by heterogeneous or homogeneous landscapes as barrier for the fungal spread
4. Outline work program
Our work plan consists of three steps:
(i) We will determine the distances that different types of spores can fly at different wind speeds. For this purpose, we will bring different fungal strains in a wind tunnel to measure their capacity for dispersal at different distances. Artificially inoculated wheat plants are the target object for these spores. We will assess the assertiveness of these fungal spores against the fungal and/or bacterial antagonists.
(ii) We will label fungal strains using stable isotopes and select bacterial isolates with natural antibiotic resistance to retrace these microorganisms in a wind tunnel (with sterile grown plants without indigenous microbial populations) and in a field plot experiment (with indigenous microbial populations) to compare their niche competition ability.
(iii) We will compare the Fusarium and Alternaria populations in different agricultural wheat fields surrounded by heterogeneous or homogeneous landscape elements to assess spatially effective spreading barriers in landscapes.
5. Linkage to ‘BioMove’ hypotheses, objectives and concepts
This project addresses the competitive coexistence of microorganisms colonizing crop plants and will clarify the relationships between dispersal ability, dispersal distances and local interactions within the plant microbiota. Competition for spatial and temporal niches as well as competitive exclusion via chemical aggression can act as stabilizing or equalizing mechanisms contributing to the coexistence of organisms (BioMove Question Q3b). The trade-offs of these dispersal processes and the niche competition could better explain the infection processes by phytopathogenic fungi and the importance of bacterial antagonists for the suppression of phytopathogens on different spatial and temporal scales (Q4).