Abstract
Plant pathogen research, so far, focused more on a single-pathogen infection, notwithstanding that wheat, in its natural ecosystem, is exposed to multiple-pathogen infection. Yet, little is known about the biology of the multiple-pathogen interactions and the role that the plant immune system plays in this pathosystem. Zymoseptoria tritici is an important wheat pathogen. In order to complete its lifecycle, Z. tritici depends on wheat. With the aim to understand the interaction between various pathogens in a co-existence-system, I conducted three experiments with two different experimental approaches, in planta and in vitro. In the 1st experiment I address the effect of an infection, of the same wheat-leaf, by Z. tritici on the subsequent infection with Pseudomonas syringae pv oryzae (Pso), a biotroph pathogen. Here I used two different Z. tritici isolates Zt05 and Zt10 because of the genetic variation. LysM and Avrstb6 are two effectors secreted by the pathogen in order to modulate the immune response of their host so the pathogen can grow and reproduce. In the 2nd experiment I address the role of these effectors in a co-existence-system. I used the same experimental approach mentioned earlier, however, I used LysM and Avrstb6 mutant strains that are generated from the isolate IPO323. In both experiments we counted the colony forming units of Pso grown on selective plates and used the number of CFUs as a read-out. In addition, I was able to show that an infection by Z. tritici impacts subsequently the growth of Pso in adjacent leaf tissue. In the last experiment I address the impact of different bacterial strains on fungal growth in vitro. These bacterial strains were collected from soil and rhizosphere of wheat. I inoculated plates with the isolates Zt05, Zt10 and ZtIPO323 then bacterial strains were inoculated at different distances from fungal spots. To analyze the impact of different bacterial strains on fungal growth, colony size of the fungi was measured. I showed that most of tested strains have a negative effect on fungal growth.
