Chemical activation of the ethylene signalling pathway promotes Fusarium graminearum resistance in detached wheat heads.

Plant signalling hormones, such as ethylene, have been shown to affect the host response to various pathogens. Often the resistance responses to necrotrophic fungi are mediated through synergistic interactions of ethylene (ET) with the jasmonate signalling pathway. On the other hand, ethylene is also an inducer of senescence and cell death, which could be beneficial for some invading necrotrophic pathogens. Fusarium graminearum, a causative agent in Fusarium head blight of wheat, is a hemibiotrophic pathogen, meaning it has both biotrophic and necrotrophic phases during the course of infection. The role of ET-signalling in the host-response to Fusarium species is however unclear: some studies indicate that ethylene mediates resistance, while others have shown that it is associated with susceptibility. These discrepancies could be related to various aspects of different experimental designs, and suggest that the role of ET-signalling in the host response to FHB is potentially dependent on interactions with some undetermined factors. To investigate whether wheat genotype can influence the ET-mediated response to FHB, the effect of chemical treatments affecting the ET pathway was studied in six wheat genotypes in detached head assays. ET-inhibitor treatments broke down resistance to both initial infection and disease spread in three resistant wheat genotypes, whereas ET-enhancer treatments resulted in reduced susceptibility in three susceptible genotypes. The results presented here show that the ET-signalling can mediate FHB resistance to F. graminearum in different wheat backgrounds.