A molecular analysis of the interaction between the biocontrol fungus Clonostachys rosea and the cereal pathogen F. graminearum

University essay from SLU/Dept. of Forest Mycology and Plant Pathology

Abstract: Modern agriculture is increasingly challenged by newly emerging crop diseases- many of them caused by fungal pathogens. At the same time, excessive application of chemical fungicides accelerates the development of resistant pathogen strains and may cause harmful effects on non-target organisms. Biological pathogen control based on living organisms is a promising component of more resilient disease management strategies, as it is thought to overcome some of the limitations of chemical control. However, for the development of more efficient biological control agents it will be crucial to gain a better understanding of the molecular interaction between the biocontrol organism and its prey. Here I studied the effect of three candidate genes on the antagonistic relationship between the biocontrol fungus Clonostachys rosea and the cereal pathogen Fusarium graminearum. The genes were selected based on their expression patterns during C. rosea in- vitro antagonism or in- vivo biocontrol and encode for the killer toxin-like chitinase CHIC1, the transcriptional regulator PRZ1 and a putative NLR-like receptor protein (NLRL). None of the candidate genes was differentially expressed in C. rosea cultures growing in dual culture with F. graminearum, however nlrl expression was increased in dual culture with Botrytis cinerea. C. rosea gene deletion strains were created through Agrobacterium- mediated transformation and screened for stress tolerance, in- vitro antagonism, and biocontrol efficiency for fusarium root rot disease. Growth rate analysis of prz1 knock-out mutants showed decreased mycelial growth on agar plates supplemented with CaCl2 or SDS. Furthermore, F. graminearum growth was increased in liquid cultures consisting of C. rosea ∆chiC1 culture filtrates. ∆nlrl was the only gene deletion strain that affected F. graminearum growth in dual culture interaction, compared to wild type. Additionally, in this experiment, none of the created deletion strains performed differentially in biocontrol assays on wheat plants infected with F. graminearum. The data highlights differences in C. rosea gene regulation during in- vitro antagonism and biocontrol and indicates involvement of NLRL during in- vitro antagonism.

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